Internet Protocol (IP) is a protocol of package net ; according to classification ISO/IT DARES is of level net (3).
The version running used of protocol IP is said also IPv4 in order to distinguish it from the most recent IPv6, been born from the requirement to manage the crescent better number than connected computers to Internet.
IP is a protocol of interconnection of nets (Inter-Networking Protocol), been born in order to interconnect heterogenous nets for technology, performances, management.
The transport protocols use you on IP are above all TCP and UDP.
Saturday, February 9, 2008
User Datagram Protocol
User Datagram Protocol (UDP) is one of the main protocols of the Suite of Internet protocols. UDP is a protocol of transport to package. It is used of usual in combination with protocol IP.
To difference of the TCP, it does not manage the riordinamento of the packages neither the rebroadcast of those lost. The UDP has like characteristic of being a protocol of inaffidabile net, protocol connectionless, but in compensation much efficient express and for the applications "to read" or Time-sensitive. In fact, it is often used for the transmission of information audio or video. Since the applications in real time often demand the minimal shipment rhythm, they do not want to delay excessive the transmission of the packages and can tolerate some loss of data, the model of service TCP can particularly not be adapted to the requirements of these applications. The UDP supplies only the basic services of the level of transport, that is:
* multiplazione of the logons, obtained through the mechanism of the doors
* verification of the errors by means of a checksum, inserted in a field of the heading of the package.
while TCP guarantees also the reliable transfer of the data, the control of flow and the control of the congestion.
UDP is a protocol stateless that is lacking in state: it does not maintain the state of the logon therefore regarding TCP it has information in less memorizzare. A serveur dedicated to a particular application that it chooses UDP as transport protocol can support many client more active ones.
To difference of the TCP, it does not manage the riordinamento of the packages neither the rebroadcast of those lost. The UDP has like characteristic of being a protocol of inaffidabile net, protocol connectionless, but in compensation much efficient express and for the applications "to read" or Time-sensitive. In fact, it is often used for the transmission of information audio or video. Since the applications in real time often demand the minimal shipment rhythm, they do not want to delay excessive the transmission of the packages and can tolerate some loss of data, the model of service TCP can particularly not be adapted to the requirements of these applications. The UDP supplies only the basic services of the level of transport, that is:
* multiplazione of the logons, obtained through the mechanism of the doors
* verification of the errors by means of a checksum, inserted in a field of the heading of the package.
while TCP guarantees also the reliable transfer of the data, the control of flow and the control of the congestion.
UDP is a protocol stateless that is lacking in state: it does not maintain the state of the logon therefore regarding TCP it has information in less memorizzare. A serveur dedicated to a particular application that it chooses UDP as transport protocol can support many client more active ones.
Server and Client
The two processes that communicate through a logon TCP have various roles:
* The process that starts one new logon TCP is said client, and sendes one demanded of logon towards one determined door.
* So that the logon comes established, on that door must is to us a serveur process "in listens", than chip ax to establish one logon TCP.
The known and recorded doors therefore are used from the serveur processes, and conventionally are associated to particular services, so that a client it knows which door to connect itself in order to catch up a determined serveur.
The serveur process, that it is in I listen on a sure door, remains blocked in attended that a client it is connected. The process client demands to establish one logon towards a determined serveur on one determined door. Normally the door source used from the client comes allotted dynamically from the operating system of the client. When the TCP establishes the logon, to both processes it comes assigned a socket through which they they can communicate between they. Typically the serveur process carries out a fork, entrusts to the son the task to communicate with the new one client and it recovers in I listen. From this point in then, client and serveur they have symmetrical roles, and they use the same instruments in order to communicate through the socket.
* The process that starts one new logon TCP is said client, and sendes one demanded of logon towards one determined door.
* So that the logon comes established, on that door must is to us a serveur process "in listens", than chip ax to establish one logon TCP.
The known and recorded doors therefore are used from the serveur processes, and conventionally are associated to particular services, so that a client it knows which door to connect itself in order to catch up a determined serveur.
The serveur process, that it is in I listen on a sure door, remains blocked in attended that a client it is connected. The process client demands to establish one logon towards a determined serveur on one determined door. Normally the door source used from the client comes allotted dynamically from the operating system of the client. When the TCP establishes the logon, to both processes it comes assigned a socket through which they they can communicate between they. Typically the serveur process carries out a fork, entrusts to the son the task to communicate with the new one client and it recovers in I listen. From this point in then, client and serveur they have symmetrical roles, and they use the same instruments in order to communicate through the socket.
Multiplazione and doors
Every active logon TCP is associated to a socket opened from a process (the socket is the instrument offered from the operating system to the applications in order to use the functionalities of the net). TCP is taken care to shunt the data between the active logons and the relati to you processes. For this, to ciascuna logon between two host it comes associated a door number on everyone of the two hosts, that bit (1-65535 is an entire one without sign to 16), contained in the appropriate field of the header.
A logon TCP therefore will be identified from IP addresses of the two hosts and from the doors used on the two hosts.
In this way, a serveur can accept logons from more client at the same time through or more doors, a client it can establish more logons towards more destinations, and is also possible that a client it at the same time establishes more independent logons towards the same door of the same serveur.
A logon TCP therefore will be identified from IP addresses of the two hosts and from the doors used on the two hosts.
In this way, a serveur can accept logons from more client at the same time through or more doors, a client it can establish more logons towards more destinations, and is also possible that a client it at the same time establishes more independent logons towards the same door of the same serveur.
Opening of one logon - Three-way handshake
The used procedure in order to establish in reliable way a logon TCP between two host is called three-way handshake (grip of hand to 3 ways), indicating the necessity to exchange 3 messages between host sender and receiving host so that the logon is created correctly. We consider as an example that the host To means to open one logon TCP with the B host; the steps to follow therefore are:
1. To it sendes a segment SYN to B - flag the SYN is set up to 1 and the Sequence field number contains value x that specific the Initial Sequence Number of To;
2. B sendes a segment SYN/ACK to To - flag SYN and ACK are set up you to 1, the Sequence field number contains the value y that specific the Initial Sequence Number di B and the Acknowledgment field number contain the value x+1 confirming the reception of the ISN of To;
3. To it sendes a segment ACK to B - the Acknowledgment field number contains the value y+1 confirming the reception of the ISN of B.
The third segment would not be, ideally, necessary for the opening of the logon in how much already after the reception from part of To of according to segment, both the hosts has expressed their availability R-all'.apertura of the logon. However it turns out necessary to the aim to allow also to the B host an esteem of the timeout begins them, like time elapsed between the shipment of a segment and the reception of correspondent ACK.
Flag the SYN turns out useful in the practical implementazione of the protocol, and in its analysis from part of the firewalls: in traffic TCP segments SYN establish new logons, while those with the flag not active belong already to established logons.
The segments use you during the handshake are usually ' single header', that is phase of synchronization between the two hosts and not of exchange of data has the Given field empty being this one.
1. To it sendes a segment SYN to B - flag the SYN is set up to 1 and the Sequence field number contains value x that specific the Initial Sequence Number of To;
2. B sendes a segment SYN/ACK to To - flag SYN and ACK are set up you to 1, the Sequence field number contains the value y that specific the Initial Sequence Number di B and the Acknowledgment field number contain the value x+1 confirming the reception of the ISN of To;
3. To it sendes a segment ACK to B - the Acknowledgment field number contains the value y+1 confirming the reception of the ISN of B.
The third segment would not be, ideally, necessary for the opening of the logon in how much already after the reception from part of To of according to segment, both the hosts has expressed their availability R-all'.apertura of the logon. However it turns out necessary to the aim to allow also to the B host an esteem of the timeout begins them, like time elapsed between the shipment of a segment and the reception of correspondent ACK.
Flag the SYN turns out useful in the practical implementazione of the protocol, and in its analysis from part of the firewalls: in traffic TCP segments SYN establish new logons, while those with the flag not active belong already to established logons.
The segments use you during the handshake are usually ' single header', that is phase of synchronization between the two hosts and not of exchange of data has the Given field empty being this one.
Timer of rebroadcast
Like described over, the timer of rebroadcast it serves to verify that every transmitted segment comes found.
The corrected formulation of this timer is difficult but a lot important, in how much a timer too much short it involves useless rebroadcasts (the timer releases while the reply or the package is still in travel), while a timer too much along it involves waits in case of loss of packages.
TCP continuously fixes the timer of rebroadcast being based on a mobile esteem to average of the Round Trip Time.
The corrected formulation of this timer is difficult but a lot important, in how much a timer too much short it involves useless rebroadcasts (the timer releases while the reply or the package is still in travel), while a timer too much along it involves waits in case of loss of packages.
TCP continuously fixes the timer of rebroadcast being based on a mobile esteem to average of the Round Trip Time.
Sequence number and Acknowledgment number
The Sequence number, or sequence number, serves to posizionare the payload of segment TCP to the inside of the data traffic.
TCP expects to receive the successive segment to the last segment received in order, that is that one whose number of sequence is equal to the number of sequence of the last segment received in order more the dimension of the payload of the same segment (that is of its Given field).
In reception, TCP it controls if the received number of sequence is that waited for one and in affirmative case it can directly send the payload to the process of applicativo level and to free the own ones buffer.
If instead it receives a number of greater sequence of that attending, deduces that or more previous segments to it have gone lost or delays to you from the level of below net. Therefore, memorizza temporary in buffer a payload of the segment for being able to deliver it to the applicativo process after to have received and delivered also to all those previous ones. From the applicativo process point of view, therefore, the data will arrive in order even if the net has altered per.qualsiasiasi.motivo this order, realizing therefore requirement of the tidy delivery of the data.
If finally the received number of sequence is inferior to that attending, the segment comes considered a duplicate of one already received and already sended to the applicativo layer, and therefore discarded. This allows to realizethe elimination of duplicates you of net.
In every segment moreover, it comes sended a Acknowledgment Number, or number of reply. The number of present reply in a segment regards the data traffic in the opposite direction. In particular, the number of sended reply gives To to B is equal to the attended number of sequence gives To and, therefore, it regards the data traffic from B to To.
Protocol TCP adopts politics of cumulative Confirmation, that means simply that the arrival of reply number indicates to receiving that the sender has received and correctly forwarded to just the applicativo process, the having segment number of equal sequence to the number of indicated reply (-1) and also all the precendenti segments to it. Therefore, in transmission, TCP temporary maintains a copy of all the data sendes to you but not still it finds to you. When it receives a number of reply for a segment, it deduces some that all the data previous to that number have been receipts correctly and therefore free just buffer from these data.
For every sended segment, TCP starts a timer, said timer of rebroadcast RTO (Retransmission Time Out). If the segment does not receive a ACK before that the timer it expires, TCP assumes that all the transmitted segments beginning from that one have gone lost and therefore ritrasmette them.
You notice yourself that, in TCP, the mechanism of the reply numbers it does not allow the receiver to communicate to the emitter that a segment has been lost, but some of the successes have been receipts (mechanism to Acknowledgment Number denied to you), therefore it is possible that for a single package lost some many must ritrasmessi. This not optimal behavior is compensated from the semplicità of the protocol. This technique is said Go-Back-N; the alternative, that is to plan the protocol of transport so that only the packages effectively lost come ritrasmessi, is said Selective Repeat (selective repetition); I use but of some optional fields I affixed allows to you I use it of the selective repetition.
The numbers of reply and the relati ones timer allow to you therefore to realize the reliable delivery, that is to guarantee that all the data send to you are delivered even if some packages they come lost from the net.
TCP expects to receive the successive segment to the last segment received in order, that is that one whose number of sequence is equal to the number of sequence of the last segment received in order more the dimension of the payload of the same segment (that is of its Given field).
In reception, TCP it controls if the received number of sequence is that waited for one and in affirmative case it can directly send the payload to the process of applicativo level and to free the own ones buffer.
If instead it receives a number of greater sequence of that attending, deduces that or more previous segments to it have gone lost or delays to you from the level of below net. Therefore, memorizza temporary in buffer a payload of the segment for being able to deliver it to the applicativo process after to have received and delivered also to all those previous ones. From the applicativo process point of view, therefore, the data will arrive in order even if the net has altered per.qualsiasiasi.motivo this order, realizing therefore requirement of the tidy delivery of the data.
If finally the received number of sequence is inferior to that attending, the segment comes considered a duplicate of one already received and already sended to the applicativo layer, and therefore discarded. This allows to realizethe elimination of duplicates you of net.
In every segment moreover, it comes sended a Acknowledgment Number, or number of reply. The number of present reply in a segment regards the data traffic in the opposite direction. In particular, the number of sended reply gives To to B is equal to the attended number of sequence gives To and, therefore, it regards the data traffic from B to To.
Protocol TCP adopts politics of cumulative Confirmation, that means simply that the arrival of reply number indicates to receiving that the sender has received and correctly forwarded to just the applicativo process, the having segment number of equal sequence to the number of indicated reply (-1) and also all the precendenti segments to it. Therefore, in transmission, TCP temporary maintains a copy of all the data sendes to you but not still it finds to you. When it receives a number of reply for a segment, it deduces some that all the data previous to that number have been receipts correctly and therefore free just buffer from these data.
For every sended segment, TCP starts a timer, said timer of rebroadcast RTO (Retransmission Time Out). If the segment does not receive a ACK before that the timer it expires, TCP assumes that all the transmitted segments beginning from that one have gone lost and therefore ritrasmette them.
You notice yourself that, in TCP, the mechanism of the reply numbers it does not allow the receiver to communicate to the emitter that a segment has been lost, but some of the successes have been receipts (mechanism to Acknowledgment Number denied to you), therefore it is possible that for a single package lost some many must ritrasmessi. This not optimal behavior is compensated from the semplicità of the protocol. This technique is said Go-Back-N; the alternative, that is to plan the protocol of transport so that only the packages effectively lost come ritrasmessi, is said Selective Repeat (selective repetition); I use but of some optional fields I affixed allows to you I use it of the selective repetition.
The numbers of reply and the relati ones timer allow to you therefore to realize the reliable delivery, that is to guarantee that all the data send to you are delivered even if some packages they come lost from the net.
Header TCP
# Source port [ 16 bit ] - the door number Identifies on the host sender associated to logon TCP.
# Destination port [ 16 bit ] - the door number Identifies on the host adressee associated to logon TCP.
# Sequence number [ 32 bit ] - Number of sequence, indicates the scostamento (expressed in byte) of the beginning of segment TCP to the inside of the complete flow, to leave from the Initial Sequence Number (ISN), negotiates R-all'.apertura of the logon.
# Acknowledgment number [ 32 bit ] - Number of reply, has only meant if flag the ACK is settato to 1, and confirmation the reception of a part of the data traffic in the opposite direction, indicating the value of the next Sequence number that the host sender of segment TCP expects to receive.
# Header Length [ 4 bit ] - bit) of the header Indicates the length (in word from 32 of segment TCP; such length can vary from 5 word (20 byte) to 15 word (60 byte) to second of the presence and the length of the optional field Options.
# Reserved [ 6 bit ] - Bit does not use you and predisposed for future developments of the protocol.
# Flags [ 6 bit ] - Bit uses you for the control of the protocol:
* URG - if settato to 1 indicates that in the flow they are present urgent data to the position (offset) indicated from the Urgent field pointer;
* ACK - if settato to 1 indicates that the Acknowledgment field number is valid;
* PSH - if settato to 1 indicates that the data in arrival do not have to be bufferizzati but passes endured to the advanced levels of the application;
* RST - if settato to 1 restores the logon; it comes used in case of serious error;
* SYN - if settato to 1 indicates that the host sender of the segment wants to open a logon TCP with the specific host adressee and in the Sequence field number the value of the Initial Sequence Number (ISN); it has the scope sincronizzare the numbers of sequence of the two hosts. The host that has sended the SYN must attend from the remote host a package SYN/ACK.
* END - if settato to 1 indicates that the host sender of the segment wants to close logon TCP opened with the host adressee. The sender attends the confirmation from receiving (with a FIN-ACK). To this point the logon is thought sluice for half: the host that has sended END will not be able more to send given, while the other host has the communication channel still available. When also the other host will send the package with set up END the logon, after the relative FIN-ACK, will be considered completely sluice.
# Advertise Window [ 16 bit ] - the dimension of the window of reception of the host Indicates sender, that is the byte number that the sender is in a position to beginning from accepting that specifying from the acknowledgment number.
# Checksum [ 16 bit ] - Field of control used for the verification of the validity of the segment. Obtained E' making the complement to 1 of the sum complement to one to 16 bit of entire header the TCP (with the field checksum put to zero) with the added one of one pseudo header composed gives: IP address sorgente(32bit), IP address destinazione(32bit), a byte of zeri, a byte that the protocol indicates and two byte that indicate the length of package TCP (header + data).
# Urgent pointer [ 16 bit ] - Gunlayer to urgent data, has only meant if flag the URG is settato to 1 and indicates the scostamento in byte to leave from the Sequence number of the byte of urgent data to the inside of the flow.
# Options - Options (optional) for uses of the protocol is left over to you.
# Destination port [ 16 bit ] - the door number Identifies on the host adressee associated to logon TCP.
# Sequence number [ 32 bit ] - Number of sequence, indicates the scostamento (expressed in byte) of the beginning of segment TCP to the inside of the complete flow, to leave from the Initial Sequence Number (ISN), negotiates R-all'.apertura of the logon.
# Acknowledgment number [ 32 bit ] - Number of reply, has only meant if flag the ACK is settato to 1, and confirmation the reception of a part of the data traffic in the opposite direction, indicating the value of the next Sequence number that the host sender of segment TCP expects to receive.
# Header Length [ 4 bit ] - bit) of the header Indicates the length (in word from 32 of segment TCP; such length can vary from 5 word (20 byte) to 15 word (60 byte) to second of the presence and the length of the optional field Options.
# Reserved [ 6 bit ] - Bit does not use you and predisposed for future developments of the protocol.
# Flags [ 6 bit ] - Bit uses you for the control of the protocol:
* URG - if settato to 1 indicates that in the flow they are present urgent data to the position (offset) indicated from the Urgent field pointer;
* ACK - if settato to 1 indicates that the Acknowledgment field number is valid;
* PSH - if settato to 1 indicates that the data in arrival do not have to be bufferizzati but passes endured to the advanced levels of the application;
* RST - if settato to 1 restores the logon; it comes used in case of serious error;
* SYN - if settato to 1 indicates that the host sender of the segment wants to open a logon TCP with the specific host adressee and in the Sequence field number the value of the Initial Sequence Number (ISN); it has the scope sincronizzare the numbers of sequence of the two hosts. The host that has sended the SYN must attend from the remote host a package SYN/ACK.
* END - if settato to 1 indicates that the host sender of the segment wants to close logon TCP opened with the host adressee. The sender attends the confirmation from receiving (with a FIN-ACK). To this point the logon is thought sluice for half: the host that has sended END will not be able more to send given, while the other host has the communication channel still available. When also the other host will send the package with set up END the logon, after the relative FIN-ACK, will be considered completely sluice.
# Advertise Window [ 16 bit ] - the dimension of the window of reception of the host Indicates sender, that is the byte number that the sender is in a position to beginning from accepting that specifying from the acknowledgment number.
# Checksum [ 16 bit ] - Field of control used for the verification of the validity of the segment. Obtained E' making the complement to 1 of the sum complement to one to 16 bit of entire header the TCP (with the field checksum put to zero) with the added one of one pseudo header composed gives: IP address sorgente(32bit), IP address destinazione(32bit), a byte of zeri, a byte that the protocol indicates and two byte that indicate the length of package TCP (header + data).
# Urgent pointer [ 16 bit ] - Gunlayer to urgent data, has only meant if flag the URG is settato to 1 and indicates the scostamento in byte to leave from the Sequence number of the byte of urgent data to the inside of the flow.
# Options - Options (optional) for uses of the protocol is left over to you.
Comparison with UDP
The main differences between TCP and UDP (User Datagram Protocol), the other main protocol of transport of the suite of Internet protocols, are:
* UDP does not offer no guarantee of the arrival the datagrammi neither on their order of arrival, in the contrary the TCP through the mechanisms of acknowledgement and rebroadcast on timeout succeeds to guarantee the delivery of the data, even if to the greater cost of overhead (a raffrontabile one visually confronting the dimension of the headings of the two protocols);
* TCP is a protocol oriented to the logon, therefore in order to establish and to pull down (and in sure cases to maintain) the logons, must send to ulterior segments of service, increasing ulteriorly the overhead of communication. To the contrary, UDP sendes only datagrammi the demands from the applicativo level;
* the object of the TCP communication is the flow of byte while that one of UDP and the single one datagramma.
I use of protocol TCP regarding UDP is, in a generalized manner, preferred when it is necessary to have guarantees on the delivery of the data or the order of arrival of several the segments (as as an example in the case of transfers of rows). To the contrary UDP it comes mainly used when the interaction between the two hosts is idempotente or in the case strong ties are had on the speed and the economy of resources of the net.
* UDP does not offer no guarantee of the arrival the datagrammi neither on their order of arrival, in the contrary the TCP through the mechanisms of acknowledgement and rebroadcast on timeout succeeds to guarantee the delivery of the data, even if to the greater cost of overhead (a raffrontabile one visually confronting the dimension of the headings of the two protocols);
* TCP is a protocol oriented to the logon, therefore in order to establish and to pull down (and in sure cases to maintain) the logons, must send to ulterior segments of service, increasing ulteriorly the overhead of communication. To the contrary, UDP sendes only datagrammi the demands from the applicativo level;
* the object of the TCP communication is the flow of byte while that one of UDP and the single one datagramma.
I use of protocol TCP regarding UDP is, in a generalized manner, preferred when it is necessary to have guarantees on the delivery of the data or the order of arrival of several the segments (as as an example in the case of transfers of rows). To the contrary UDP it comes mainly used when the interaction between the two hosts is idempotente or in the case strong ties are had on the speed and the economy of resources of the net.
Transmission Control Protocol
Transmission Control Protocol (TCP) is the protocol of level of transport of the Suite of Internet protocols. It is defined in RFC 793, and on it great part of the Internet applications is leaned.
The TCP can approximately be classified to the level transport (DARES level 4) of the reference model DARES, and of usual IP is used in combination with the level protocol net (DARES level 3 ). The correspondence with the model DARES is not perfect, in how much the TCP and the IP is born before. Their combination is indicated like TCP/IP and, to the times, erroneously an only protocol is considered.
TCP is planned in order to use the services of protocol IP, than it does not offer some guarantee in order to the delivery of the packages, to the delay, the congestion, and to construct a reliable communication channel between two processes applied to you. The communication channel is constituted from a bidirectional flow of byte. Moreover, some functionalities of TCP are vital for the good total operation of one net IP.
The TCP nacque in 1970 as fruit of the job of a group of search of the department of American defense. Its head of force are the high reliability and robustness. Its popolarità must also to thanks to one its implementazione diffused from the University of Berkeley in California under source shape.
The TCP can approximately be classified to the level transport (DARES level 4) of the reference model DARES, and of usual IP is used in combination with the level protocol net (DARES level 3 ). The correspondence with the model DARES is not perfect, in how much the TCP and the IP is born before. Their combination is indicated like TCP/IP and, to the times, erroneously an only protocol is considered.
TCP is planned in order to use the services of protocol IP, than it does not offer some guarantee in order to the delivery of the packages, to the delay, the congestion, and to construct a reliable communication channel between two processes applied to you. The communication channel is constituted from a bidirectional flow of byte. Moreover, some functionalities of TCP are vital for the good total operation of one net IP.
The TCP nacque in 1970 as fruit of the job of a group of search of the department of American defense. Its head of force are the high reliability and robustness. Its popolarità must also to thanks to one its implementazione diffused from the University of Berkeley in California under source shape.
IPX on Ethernet
IPX can be transmitted on Ethernet using one of the four following types of incapsulazione:
* 802.3 (raw) come used in the systems "legacy" and preview that data IPX begin immediately after frame header the 802.3. The packages begin with Destination Ethernet Address (6 byte), Source Ethernet Address (6 byte), Frame Length (2 byte), are followed from data IPX. These last ones always begin with two byte 0xFF (Checksum field), that two can be used in order to differentiate this type of incvapsulazione IPX from the others.
* 802.2 (Novell) comprises frame header 802,3 (destination, source, length) followed from header a LLC (3 byte - 0xE0, 0xE0, 0x03) followed from data IPX. The field 0xE0 of header the LLC is for protocol ' Novell'.
* 802.2 (SNAP) comprise frame header 802,3, header a LLC (3 byte - 0xAA, 0xAA, 0x03), header a SNAP (5 byte - 0x00, 0x00, 0x00, 0x81, 0x37) and fdati the IPX. The fields 0xAA of header the LLC are for protocol ' SNAP'. The first three byte of header the SNAP are a OUI are followed from 2 byte ofEtherType IPX.
* Ethernet II comprises one frame header Ethernet II (Destination, Source, EtherType) followed from data IPX.
* 802.3 (raw) come used in the systems "legacy" and preview that data IPX begin immediately after frame header the 802.3. The packages begin with Destination Ethernet Address (6 byte), Source Ethernet Address (6 byte), Frame Length (2 byte), are followed from data IPX. These last ones always begin with two byte 0xFF (Checksum field), that two can be used in order to differentiate this type of incvapsulazione IPX from the others.
* 802.2 (Novell) comprises frame header 802,3 (destination, source, length) followed from header a LLC (3 byte - 0xE0, 0xE0, 0x03) followed from data IPX. The field 0xE0 of header the LLC is for protocol ' Novell'.
* 802.2 (SNAP) comprise frame header 802,3, header a LLC (3 byte - 0xAA, 0xAA, 0x03), header a SNAP (5 byte - 0x00, 0x00, 0x00, 0x81, 0x37) and fdati the IPX. The fields 0xAA of header the LLC are for protocol ' SNAP'. The first three byte of header the SNAP are a OUI are followed from 2 byte ofEtherType IPX.
* Ethernet II comprises one frame header Ethernet II (Destination, Source, EtherType) followed from data IPX.
Internetwork Packet Exchange
The Internetwork Packet Exchange (IPX) is a Protocol of net to the level network of the model DARES, of the battery of protocols IPX/SPX, that it came used in origin for the exchange of packages in the nets NetWare di Novell. Because of the popolarità of NetWare between the end of years 1980 and the half of years 1990, the IPX divenne a protocol of internetworking much diffusing. Novell derived the IPX from protocol IDP of Xerox Network Services.
The IPX use is in a generalized manner decline in how much the boom of Internet has rendered the TCP/IP practically universal. Computers and nets can use more protocols than net, therefore nearly all situated the IPX use also TCP/IP in order to allow the connettività to Internet. It is also possible to use the products of Novell without IPX, in how much NetWare supports is IPX that TCP/IP end from version 5.
The IPX use is in a generalized manner decline in how much the boom of Internet has rendered the TCP/IP practically universal. Computers and nets can use more protocols than net, therefore nearly all situated the IPX use also TCP/IP in order to allow the connettività to Internet. It is also possible to use the products of Novell without IPX, in how much NetWare supports is IPX that TCP/IP end from version 5.
NetBIOS Characteristic
NetBIOS offers always three services:
* Service Name: recording and resolution of the name (the search of the name is part ofthe SMB, a advanced level)
* Service Session: oriented reliable communication to the logon
* Service Datagram distribution: communication not trusted without logon
When NetBIOS was a protocol working to the level datalink (given level of connection) of the model DARES, its functions was accessible throughthe interrupt 5Ch. The messages pass you to these functions were formatta to you to second of the format of the Network Block Control.
NetBIOS and NetBEUI are only assign you to the use on the local nets. For this reason, they do not have the support for the routing and can manage a maximum of 72 nodes. The use of the transmissions is intense, especially for the operations connected to the name service.
NBT (NetBIOS on TCP/IP) uses or a more NBNS (NetBIOS Name Serveur) in order to cover the service of the names on subnet multiple (while the transmission - broadcast - is limited to an only one subnet). A NBNS is one species of dynamic DNS. The implementazione Microsoft of NBNS is called WINS. Moreover, in order to extend the virtual nets NetBIOS through multiple under-nets to IP, the standard has introduced the use of one or more serveur NBDD (NetBIOS Datagram Distribution). The implementazione of NBDD of Microsoft has not never worked.
* Service Name: recording and resolution of the name (the search of the name is part ofthe SMB, a advanced level)
* Service Session: oriented reliable communication to the logon
* Service Datagram distribution: communication not trusted without logon
When NetBIOS was a protocol working to the level datalink (given level of connection) of the model DARES, its functions was accessible throughthe interrupt 5Ch. The messages pass you to these functions were formatta to you to second of the format of the Network Block Control.
NetBIOS and NetBEUI are only assign you to the use on the local nets. For this reason, they do not have the support for the routing and can manage a maximum of 72 nodes. The use of the transmissions is intense, especially for the operations connected to the name service.
NBT (NetBIOS on TCP/IP) uses or a more NBNS (NetBIOS Name Serveur) in order to cover the service of the names on subnet multiple (while the transmission - broadcast - is limited to an only one subnet). A NBNS is one species of dynamic DNS. The implementazione Microsoft of NBNS is called WINS. Moreover, in order to extend the virtual nets NetBIOS through multiple under-nets to IP, the standard has introduced the use of one or more serveur NBDD (NetBIOS Datagram Distribution). The implementazione of NBDD of Microsoft has not never worked.
NetBIOS
NetBIOS is a level protocol session, developed from IBM and Sytec for the so-called PC-Network to the beginning of years ' 80. Although it has been published single in a handbook of IBM, the BEES of the divennero protocol of fact standard.
From when the PC-Network more it is not used, being be replaced from the nets TokenRing and Ethernet, the NetBIOS protocol could not be more necessary. But since many programs are written for the BEES of NetBIOS, they have been adapted in order to work on other protocols like IPX/SPX and TCP/IP.
NetBIOS on TokenRing or called Ethernet is hour NetBEUI (NetBIOS Extended User Interface). It was still a lot used until the operating system Microsoft Windows 98 has been rilasciato. NetBIOS on TCP/IP is called NBT and has been standardized from RFC 1001 and 1002. NBT offers to a emulazione based on NetBIOS of PC-Network LAN on one net based on IP. This protocol has been introduced with Microsoft Windows 2000 and is the preferred transport on NetBIOS.
From when the PC-Network more it is not used, being be replaced from the nets TokenRing and Ethernet, the NetBIOS protocol could not be more necessary. But since many programs are written for the BEES of NetBIOS, they have been adapted in order to work on other protocols like IPX/SPX and TCP/IP.
NetBIOS on TokenRing or called Ethernet is hour NetBEUI (NetBIOS Extended User Interface). It was still a lot used until the operating system Microsoft Windows 98 has been rilasciato. NetBIOS on TCP/IP is called NBT and has been standardized from RFC 1001 and 1002. NBT offers to a emulazione based on NetBIOS of PC-Network LAN on one net based on IP. This protocol has been introduced with Microsoft Windows 2000 and is the preferred transport on NetBIOS.
System DNS in Internet
Whichever net IP can use the DNS in order to implement a its private system of names. However, the term "dominion name" more commonly is used when it refers to the public system of the DNS on Internet. This is based on 13 "root serveur" universal, whose IP addresses are distributed independently from the DNS through rows said "root hints" (literally: indications for the root). From this serveur main, the DNS comes then delegated to other serveur DNS that is taken care of the names to the inside of specific parts of the space of names DNS.
Ten of the thirteen root serveur are, at least nominally, situate to you in the USA. However, given the access to many of they it is realized through indirizzamento anycast, that it allows to assign to more computer same IP address in order to supply a uniform service on immense geographic areas, the greater part of the serveur are in effects localizes you to outside of the United States.
The owner of a dominion name rintracciabile in a database is called WHOIS: for many dominions of first level a WHOIS base is managed from the IANA, with the WHOIS detailed maintained from the recording authority that controls that dominion. For more than 240 national dominions the recording authority manages in exclusive right the WHOIS for the competence dominion.
Ten of the thirteen root serveur are, at least nominally, situate to you in the USA. However, given the access to many of they it is realized through indirizzamento anycast, that it allows to assign to more computer same IP address in order to supply a uniform service on immense geographic areas, the greater part of the serveur are in effects localizes you to outside of the United States.
The owner of a dominion name rintracciabile in a database is called WHOIS: for many dominions of first level a WHOIS base is managed from the IANA, with the WHOIS detailed maintained from the recording authority that controls that dominion. For more than 240 national dominions the recording authority manages in exclusive right the WHOIS for the competence dominion.
Zones, delegations and retorts
A zone DNS is a part of the space of the names, constituted from a delegated dominion and its sottodomini that they are not to they time, that it is under a same administrative management and therefore is managed from one or more serveur.
The management of a zone is delegated from the advanced zone through of the records of type NS. As an example, in the zone org there will be a delegation for the zone wikipedia.org to serveur DNS that manages it. For redundancy reasons, ciascuna zone is replied on more server, and consequently the delegation is constituted from more record NS, that they indicate that everyone of the server indicates to you contains the information for that zone (that is is autoritativo for the zone).
Various the serveur that they are delegated for a zone would have to contain the same information, so that one whichever of these can answer to one query for a record of the zone.
The retort outline typically previews that there is a server master (primary), that it is that one on which come modernized the information, and or a more server Slavic (secondary), that they copy the information from the master when necessary. In order to hold trace delle various "versions" of a zone that can are to us in circulation, and particular in order to allow to a secondary one to decide if it must transfer the zone dal primary, every zone has a number of series, that every time must be increased that come made modifications sul primary. In order to obtain the number of series of a present zone on a server, one is carried out interrogation of type SOA. The secondary one confronts just the number of series with that one of the head physician, and if that one of the primary one is advanced it transfers the zone.
The operation of copy of all the records of a zone from the master to one Slavic is said zones transfer, and can be complete (all the content of the zone comes copied) or increases them (comes only copied the records modified regarding the already present version.
Some implementazioni of DNS allow to modify the zones from whichever autoritativo server, propagando the modifications on the other server.
The root (root) of the tree of names DNS is the zone. (point), that it is managed from with of serveur calls root serveur exactly to you.
The management of a zone is delegated from the advanced zone through of the records of type NS. As an example, in the zone org there will be a delegation for the zone wikipedia.org to serveur DNS that manages it. For redundancy reasons, ciascuna zone is replied on more server, and consequently the delegation is constituted from more record NS, that they indicate that everyone of the server indicates to you contains the information for that zone (that is is autoritativo for the zone).
Various the serveur that they are delegated for a zone would have to contain the same information, so that one whichever of these can answer to one query for a record of the zone.
The retort outline typically previews that there is a server master (primary), that it is that one on which come modernized the information, and or a more server Slavic (secondary), that they copy the information from the master when necessary. In order to hold trace delle various "versions" of a zone that can are to us in circulation, and particular in order to allow to a secondary one to decide if it must transfer the zone dal primary, every zone has a number of series, that every time must be increased that come made modifications sul primary. In order to obtain the number of series of a present zone on a server, one is carried out interrogation of type SOA. The secondary one confronts just the number of series with that one of the head physician, and if that one of the primary one is advanced it transfers the zone.
The operation of copy of all the records of a zone from the master to one Slavic is said zones transfer, and can be complete (all the content of the zone comes copied) or increases them (comes only copied the records modified regarding the already present version.
Some implementazioni of DNS allow to modify the zones from whichever autoritativo server, propagando the modifications on the other server.
The root (root) of the tree of names DNS is the zone. (point), that it is managed from with of serveur calls root serveur exactly to you.
Tipologie of record
To a name DNS various types of information can correspond. For this reason, various types of record DNS exist. Every voice of database the DNS must be characterized from a type. The main types are:
* Most common it is the so-called record "To", that it indicates the correspondence between a name and one (or more) IP addresses (for the precision you address IPv4, that is the version currently in use).
* The records of type "MX" (Mail eXchange) indicate to which serveur must be sended the e-mail for a sure dominion.
* The records of type "CNAME" are used in order to create a alias, that is in order to make so that the same calculating is famous with more names. The main scope of such record is that one of being able to give of the names to of the services, therefore from being able to catch up the same service without having by force to know the machine (its name or its IP address) on which it is accommodated.
* The DNS comes used also in order to realize the inverse resolution, that is in order to make to correspond to an IP address the correspondent name to dominion. For this the records of type "PTR" are used (and an appropriate zone of the space of the names in-addr.arpa).
* The IPv6 addresses are record with record of type "AAAA" (this to you recall that a IPv6 address is 4 times longer than a IPv4 address).
* The records of type "SRV" serve to identify the serveur for a determined service to the inside of a dominion. They can be considers you one generalization of records MX.
There are also types of records "of service", necessary to the distributed operation of the database:
* Records "NS" (Name Serveur) are use you in order to indicate which are serveur DNS autoritati you for a sure dominion, that is in order to delegate of the management.
* Records "SOA" (Start of Authority) are used for the management of zones DNS.
In the DNS other types of record can be immessi, some folkloristic ones, like "LOC", used (little) in order to bring back the geographic coordinates of a situated one, others add emergency functions in order to avoid manomissioni.
* Most common it is the so-called record "To", that it indicates the correspondence between a name and one (or more) IP addresses (for the precision you address IPv4, that is the version currently in use).
* The records of type "MX" (Mail eXchange) indicate to which serveur must be sended the e-mail for a sure dominion.
* The records of type "CNAME" are used in order to create a alias, that is in order to make so that the same calculating is famous with more names. The main scope of such record is that one of being able to give of the names to of the services, therefore from being able to catch up the same service without having by force to know the machine (its name or its IP address) on which it is accommodated.
* The DNS comes used also in order to realize the inverse resolution, that is in order to make to correspond to an IP address the correspondent name to dominion. For this the records of type "PTR" are used (and an appropriate zone of the space of the names in-addr.arpa).
* The IPv6 addresses are record with record of type "AAAA" (this to you recall that a IPv6 address is 4 times longer than a IPv4 address).
* The records of type "SRV" serve to identify the serveur for a determined service to the inside of a dominion. They can be considers you one generalization of records MX.
There are also types of records "of service", necessary to the distributed operation of the database:
* Records "NS" (Name Serveur) are use you in order to indicate which are serveur DNS autoritati you for a sure dominion, that is in order to delegate of the management.
* Records "SOA" (Start of Authority) are used for the management of zones DNS.
In the DNS other types of record can be immessi, some folkloristic ones, like "LOC", used (little) in order to bring back the geographic coordinates of a situated one, others add emergency functions in order to avoid manomissioni.
Names DNS
A name to dominion is constituted from one series of stringhe separated from points, as an example it.wikipedia.org. To difference of IP addresses, where the more important part of the number is before leaving from left, in a name DNS the part more important is before leaving from right. This is said dominion of first level (or TLD, Top Level Domain), as an example org or it.
A dominion of second level consists in two parts, as an example wikipedia.org, and therefore via. Every ulterior specific element an ulterior subdivision. When a dominion of second level comes recorded the awardee, this is authorized to use the relative names of dominion you to the successes to you levels as itwikipedia.org (dominion of third level) and others as some.other.stuff.wikipedia.org (dominion of fifth level) and therefore via.
A dominion of second level consists in two parts, as an example wikipedia.org, and therefore via. Every ulterior specific element an ulterior subdivision. When a dominion of second level comes recorded the awardee, this is authorized to use the relative names of dominion you to the successes to you levels as itwikipedia.org (dominion of third level) and others as some.other.stuff.wikipedia.org (dominion of fifth level) and therefore via.
DNS Motivations and uses
* The possibility to attribute a testuale name easy memorizzare to a serveur (as an example a situated World Wide Web) improves a lot the use of the service, in how much the human beings find easier to remember testuali names (while the hosts and the router are raggiungibili using numerical IP addresses). For this, the DNS is fundamental for the wide spread of Internet also between not technical customers, and is one of its more visible characteristics.
* It is possible to attribute more names to same IP address (or viceversa) in order to represent various services or functions supplied from a same host (or more host that distributes the same service. This flexibility turns out useful in many cases:
o In the case the serveur must replace the serveur that accommodates a service, or its IP address must be modified, is sufficient to modify record DNS, without having to take part on the client.
o I use much popular one of this possibility is the so-called one virtual hosting based on the names, one technical for which an endowed web server of a single interface of net and single IP address it can accommodate more situated web, using the alphanumeric address transmitted in header the HTTP in order to identify the situated one for which it comes made the demand.
o Using various names in order to refer to the various services it distributes to you from a host, it is possible to move a part of the services on an other host, and to move client on the this new host being modified its records in the DNS.
o Making to correspond more IP addresses to a name, the cargo of the client comes distributed on various serveur, obtaining an increase of the total performances of the service and a tolerance to the breakdowns (but it is necessary to make sure itself that various the serveur is always aligns to you, that is offer the same service exactly to the client).
* The inverse resolution is useful in order to identify the identity of a host, or in order to read the result of a traceroute.
* The DNS comes used from numerous technologies in little visible way the customers, in order to organize the necessary information to the operation of the service.
* It is possible to attribute more names to same IP address (or viceversa) in order to represent various services or functions supplied from a same host (or more host that distributes the same service. This flexibility turns out useful in many cases:
o In the case the serveur must replace the serveur that accommodates a service, or its IP address must be modified, is sufficient to modify record DNS, without having to take part on the client.
o I use much popular one of this possibility is the so-called one virtual hosting based on the names, one technical for which an endowed web server of a single interface of net and single IP address it can accommodate more situated web, using the alphanumeric address transmitted in header the HTTP in order to identify the situated one for which it comes made the demand.
o Using various names in order to refer to the various services it distributes to you from a host, it is possible to move a part of the services on an other host, and to move client on the this new host being modified its records in the DNS.
o Making to correspond more IP addresses to a name, the cargo of the client comes distributed on various serveur, obtaining an increase of the total performances of the service and a tolerance to the breakdowns (but it is necessary to make sure itself that various the serveur is always aligns to you, that is offer the same service exactly to the client).
* The inverse resolution is useful in order to identify the identity of a host, or in order to read the result of a traceroute.
* The DNS comes used from numerous technologies in little visible way the customers, in order to organize the necessary information to the operation of the service.
Domain Name System
Domain Name System (often indicated with DNS) is a service used for the resolution of names of host in IP addresses and viceversa. The service is realized through a database distributed, constituted from serveur DNS.
Name DNS denotes also the protocol that regulated the operation of the service, the programs that implements it, the serveur on which these they turn, with of this serveur that they cooperate in order to supply the service.
Names DNS, or "names of I dominate", are one of the characteristics more visible than Internet.
There is confusion with respect to the definition of the acronym: the S often comes interpreted like service, but the correct definition is system.
The operation to convert a name in an address is said resolution DNS, to convert an IP address in name is said inverse resolution.
Name DNS denotes also the protocol that regulated the operation of the service, the programs that implements it, the serveur on which these they turn, with of this serveur that they cooperate in order to supply the service.
Names DNS, or "names of I dominate", are one of the characteristics more visible than Internet.
There is confusion with respect to the definition of the acronym: the S often comes interpreted like service, but the correct definition is system.
The operation to convert a name in an address is said resolution DNS, to convert an IP address in name is said inverse resolution.
Implementazioni for the various systems operated to you
Of the server and the implementazione functions client NTP are available for various systems operated to you, between which Windows , Linux and MacOS X. Devices exist also independent you plan to you in order to carry out the function of server NTP.
Of continuation the usable procedures and commandos are brought back in order sincronizzare just the computer with a server NTP.
Of continuation the usable procedures and commandos are brought back in order sincronizzare just the computer with a server NTP.
NTP Operation
The NTP is one of the oldest protocols still in use, and is reached its quarter version. It was developed near the university of the Delaware from Dave Mills, than of it it follows still the development. The operation is based on the survey of the times of latenza in the transit of the packages on the net. It uses the universal co-ordinate time and he is therefore independent from the jet lag ones. Currently it is in a position to sincronizzare the clocks of the computers on Internet within a margin of 10 milliseconds and with one accuracy at least 200 microsecond ones to inside of one LAN in optimal conditions.
Various serveur NTP is organizes to you in a hierarchical structure of "layers", where layer 1 is synchronized with an external temporal source which an atomic clock, GPS or a radiocontrollato clock, layer 2 receives the temporal data from serveur of layer 1, and therefore via. A various serveur sincronizza confronting its clock with that one of other serveur of advanced layer or the same layer. This allows to increase the precision, and to eliminate eventual serveur scorretti.
Various serveur NTP is organizes to you in a hierarchical structure of "layers", where layer 1 is synchronized with an external temporal source which an atomic clock, GPS or a radiocontrollato clock, layer 2 receives the temporal data from serveur of layer 1, and therefore via. A various serveur sincronizza confronting its clock with that one of other serveur of advanced layer or the same layer. This allows to increase the precision, and to eliminate eventual serveur scorretti.
Network Time Protocol
The Network Time Protocol, in acronym NTP, is a protocol in order sincronizzare the clocks of the computers to the inside of one net to package commutation, therefore with variable and inaffidabili times of latenza. The NTP is a protocol client-serveur pertaining to the applicativo level.
Authentication and authorization
For emergency reasons, the making systems part of a net SNMP come group in one so-called community to you. The community is identified from one tightens of 32 byte and every system can belong more than one than these. Agent the only demanded SNMP chip ax from a manager of the same community. The authorization of the members of a community to operate on an object can be of three types:
* read: the manager it can interrogate the agent in order to only know the state of system (only GET)
* write: where the manager it can also vary of formulation (GET and SET)
* trap: the agent it can send trap to the manager
* read: the manager it can interrogate the agent in order to only know the state of system (only GET)
* write: where the manager it can also vary of formulation (GET and SET)
* trap: the agent it can send trap to the manager
SNMP Architecture
The three fundamental members of framework the SNMP are:
1. it arranges managed (managed object)
2. management agent (management agent)
3. he arranges of management (manager)
Every managed system (as an example a simple node, a router, printing or whichever other device that supplies an interface of management SNMP) usually accommodates a management agent (master agent) and a sure number of subagent. The master agent it has at least the role of intermediary between the manager (that it is the remote application that takes the management decisions, as an example under the direct control of the human operator) and the subagent (that they are the executory ones of such decisions). Every subagent is person in charge to relatively put into effect the decisions of management in the context of a particular subsystem or to a particular aspect of the managed system. In systems that supply particularly simple mechanisms of management, master agent and subagent they can meet in an only member able software is to converse with the manager that to put into effect of the decisions; in this case it will be spoken simply about agent.
SNMP uses one clear separation between the protocol of management and the structure of the managed object. In architecture SNMP, for every given subsystem Management Information Base is defined a base said MIB(), managed from the correspondent subagent, which represents the state of the managed subsystem, or better, a projection than such state limited to the aspects of which the management is wanted to be concurred. Draft of a base given that it could be defined, mutuando a term from the reflection, "causal connected": in other words, every modification to the MIB cause a correspondent change in the state of the represented subsystem, and viceversa. To guarantee this property of the MIB is the main function of the subagent that it manages it.
The access to the MIB (in reading and writing) representsthe interface supplied to the manager in order to manage the system. Every MIB, also varying in the specific contents, has the same general structure and the same mechanisms generate them of access from part of manager (the reading and writing of the data). Thanks to the logon motive of the MIB, it is therefore possible to the manager to act on the state of the subsystem in a way that is widely independent from the concrete procedures that must be put in action (from the subagent) in order to extract the information of state represented in the MIB, or to put into effect the state modifications as a result of changes of the contents of the MIB. Therefore, as an example, a MIB data could be had that represents IP address of the managed system; in order to modify such address, to the manager he is sufficient to approach the MIB sovrascrivendo the corresponding data, prescinding of the details of as a such modification comes then concretely "put into effect" on the managed system.
More in detail, the manager it converses with the systems managed essentially in two ways: it sendes demands SNMP and it receives notifications SNMP.
1. it arranges managed (managed object)
2. management agent (management agent)
3. he arranges of management (manager)
Every managed system (as an example a simple node, a router, printing or whichever other device that supplies an interface of management SNMP) usually accommodates a management agent (master agent) and a sure number of subagent. The master agent it has at least the role of intermediary between the manager (that it is the remote application that takes the management decisions, as an example under the direct control of the human operator) and the subagent (that they are the executory ones of such decisions). Every subagent is person in charge to relatively put into effect the decisions of management in the context of a particular subsystem or to a particular aspect of the managed system. In systems that supply particularly simple mechanisms of management, master agent and subagent they can meet in an only member able software is to converse with the manager that to put into effect of the decisions; in this case it will be spoken simply about agent.
SNMP uses one clear separation between the protocol of management and the structure of the managed object. In architecture SNMP, for every given subsystem Management Information Base is defined a base said MIB(), managed from the correspondent subagent, which represents the state of the managed subsystem, or better, a projection than such state limited to the aspects of which the management is wanted to be concurred. Draft of a base given that it could be defined, mutuando a term from the reflection, "causal connected": in other words, every modification to the MIB cause a correspondent change in the state of the represented subsystem, and viceversa. To guarantee this property of the MIB is the main function of the subagent that it manages it.
The access to the MIB (in reading and writing) representsthe interface supplied to the manager in order to manage the system. Every MIB, also varying in the specific contents, has the same general structure and the same mechanisms generate them of access from part of manager (the reading and writing of the data). Thanks to the logon motive of the MIB, it is therefore possible to the manager to act on the state of the subsystem in a way that is widely independent from the concrete procedures that must be put in action (from the subagent) in order to extract the information of state represented in the MIB, or to put into effect the state modifications as a result of changes of the contents of the MIB. Therefore, as an example, a MIB data could be had that represents IP address of the managed system; in order to modify such address, to the manager he is sufficient to approach the MIB sovrascrivendo the corresponding data, prescinding of the details of as a such modification comes then concretely "put into effect" on the managed system.
More in detail, the manager it converses with the systems managed essentially in two ways: it sendes demands SNMP and it receives notifications SNMP.
Simple Network Management Protocol
SNMP (Simple Network Management Protocol) belongs to the suite of Internet protocols defined from the IETF (Internet Engineering Task Force). The protocol operates to level 7 of the model DARES. It concurs the management and the supervision of apparatuses connects to you in a net, regarding all those aspects that demand actions of administrative type.
Companies that support LDAP
LDAP has obtained a wide support from companies which:
* Apache (through Apache Directory Serveur)
* Apple (through Open Directory/OpenLDAP)
* AT&T
* Banyan
* HP
* IBM/Lotus
* ISODE (through M-Vault serveur)
* Microsoft (through Active Directory)
* Netscape (today in the products Sun Microsystems and Red Hat)
* Novell (through eDirectory)
* OctetString (through VDE serveur)
* Oracle (through Oracle Internet Directory)
* Radiant Logic (through RadiantOne Virtual Directory Serveur)
* Red Hat (through Red Hat Directory Serveur)
* SiemensAG (through DirX serveur)
* SGI
* Sun (through directory the serveur iPlanet and Sun ONE)
* Symlabs (through Directory Extender)
beyond that in free implementazioni opensource/ software which OpenLDAP and Fedora Directory Serveur. AlsoApache HTTP Serveur used as proxy (from the module mod_proxy) supports LDAP.
* Apache (through Apache Directory Serveur)
* Apple (through Open Directory/OpenLDAP)
* AT&T
* Banyan
* HP
* IBM/Lotus
* ISODE (through M-Vault serveur)
* Microsoft (through Active Directory)
* Netscape (today in the products Sun Microsystems and Red Hat)
* Novell (through eDirectory)
* OctetString (through VDE serveur)
* Oracle (through Oracle Internet Directory)
* Radiant Logic (through RadiantOne Virtual Directory Serveur)
* Red Hat (through Red Hat Directory Serveur)
* SiemensAG (through DirX serveur)
* SGI
* Sun (through directory the serveur iPlanet and Sun ONE)
* Symlabs (through Directory Extender)
beyond that in free implementazioni opensource/ software which OpenLDAP and Fedora Directory Serveur. AlsoApache HTTP Serveur used as proxy (from the module mod_proxy) supports LDAP.
DSML
Recently, the need to join operations LDAP with XML in the use of the Web Services has given to the light a new called language Directory Services Markup Language (DSML). The most recent version is DSMLv2. DSML is a generic format for importare/esportare such information. In DSML the data of the directory can be were flavored between applications that support such format without to expose to the protocol 17 LDAP. XML offers a effective method in order to introduce and to transfer the data; the services of directory allow to share and to manage the data and are therefore a prerequirement necessary in order to carry out operations online. DSML is planned in order to render the service of directory more dynamic employing XML. DSML is an outline in XML in order to work with the directory, and is defined with a Document Content Description (DCD). Therefore DSML allows the programmatori of XML to approach directory the LDAP without having to that to make with interface LDAP or BEES for the access the directory, offering a consisting way in order to work with directory multiple and different.
Ldap has influenced the development of other protocols of net, like the Service Provisioning Markup Language (SPML) and the Service Location Protocol.
Ldap has influenced the development of other protocols of net, like the Service Provisioning Markup Language (SPML) and the Service Location Protocol.
LDAP
It wanted but an interface to directory a serveur X.500 that used little resources or a light protocol. For this reason it came developed LDAP, like alternative snella to the DAP. LDAP demands lightest and popular protocol TCP/IP instead of the battery DARES. Moreover LDAP simplifies sure operations of X.500 and omits sure intricati aspects. The protocol has been devised from Tim Howes di Netscape, Steve Kille of ISODE and Mark Angle di Critical Angle Inc..
Two premonitory ones of LDAP are represent to you from the RFC rilasciati from IETF, Directory Assistance Service (RFC 1202) and DIXIE Protocol Specification (RFC 1249). They are both RFC informed to you and they did not come proposals like standard. Directory assistance service (the DAS) defined a method for which a directory client it can communicate with a proxy on a host DARES that rilasciava demanded X.500 to name of the client. DIXIE is similar to DAS, but it more offers one directed conversion of the DAP. The first version of LDAP came defined in X.500 Lightweight Access Protocol (RFC 1487), replaced from Lightweight Directory Access Protocol (RFC 1777).
More ahead LDAP refined to the ideas and the protocols of DAS and DIXIE. It has a more neutral implementazione and it reduces the complexity of the client. The greater part of the jobs in DIXIE and LDAP comes from the University of Michigan, that it offers a documentation of the implementazioni of LDAP and maintains Web pages and mailing list on LDAP. RFC 1777 defines same protocol LDAP, with with: "the rappresentazione in Stringhe and Sintassi of the Attributes Standard" (RFC 1778), "Rappresentazione in Tightens of the Distinguished Name" (RFC 1779), "Formed for URL LDAP" (RFC 1959), "Rappresentazione in tightens of the filters of search LDAP" (RFC 1960) LDAP version 2 has obtained the state of standard rough draft in the process of standardization IETF, a step the being one standard. Today, all the implementazione of directory the serveur are base on LDAP version to you 3.
Two premonitory ones of LDAP are represent to you from the RFC rilasciati from IETF, Directory Assistance Service (RFC 1202) and DIXIE Protocol Specification (RFC 1249). They are both RFC informed to you and they did not come proposals like standard. Directory assistance service (the DAS) defined a method for which a directory client it can communicate with a proxy on a host DARES that rilasciava demanded X.500 to name of the client. DIXIE is similar to DAS, but it more offers one directed conversion of the DAP. The first version of LDAP came defined in X.500 Lightweight Access Protocol (RFC 1487), replaced from Lightweight Directory Access Protocol (RFC 1777).
More ahead LDAP refined to the ideas and the protocols of DAS and DIXIE. It has a more neutral implementazione and it reduces the complexity of the client. The greater part of the jobs in DIXIE and LDAP comes from the University of Michigan, that it offers a documentation of the implementazioni of LDAP and maintains Web pages and mailing list on LDAP. RFC 1777 defines same protocol LDAP, with with: "the rappresentazione in Stringhe and Sintassi of the Attributes Standard" (RFC 1778), "Rappresentazione in Tightens of the Distinguished Name" (RFC 1779), "Formed for URL LDAP" (RFC 1959), "Rappresentazione in tightens of the filters of search LDAP" (RFC 1960) LDAP version 2 has obtained the state of standard rough draft in the process of standardization IETF, a step the being one standard. Today, all the implementazione of directory the serveur are base on LDAP version to you 3.
Lightweight Directory Access Protocol
In computer science LDAP (Lightweight Directory Access Protocol) it is a protocol standard for the interrogation and the modification of the services of directory. In the years seventy integration between the world of the communication and the computer science technologies traced the road towards the development of new technologies of communication. Many between the systems develop to you were incompatible between of they: divenne obvious that was necessary standard that they allowed to equipment and it arranges different to cooperate. They came develops two main standards independently to you. One came devised from the CCITT (Comite Consultatif International Telephonique ET Telegraphique, or International Consultative Committee on Telephony and Telegraphy), and fromthe ISO. CCITT divenne then ITU-T. The job produced to OSI Reference Model (ISO the 7498), that it more low characterized seven layers in the communication of data with the physical transport to the level, and protocols of the application to the higher levels. The other standards were developed ahead with with Internet and the search capacity from the DARPA in the USA. The Internet Architecture Board (IAB) and Internet Engineering Task Force (IETF), develop standard for Internet with a document series call Request For Comments to you (RFC), than after to be it approves of to you, it implements to you and used for a sure period, they can become standard (STD). Before that one proposed becomes a RFC, is called Internet Draft.
These two processes of standardization face the problem from two perspective different. The approach DARES begins from zero and defines standard using a formal model without to demand implementazioni. Internet uses a less formal approach, where anyone can propose and to comment RFC that comes then implements to you in order to verify of the feasibility. The protocols DARE are develop to you slowly, especially in the market of personal the computers. To contrary TCP/IP and Internet they have had a greater application and they are develops to you quickly. Some companies developed therefore to the own protocols and products for the network. In any case the protocols DARE had importance in the large distributed systems that they were being developed in particular way. An important area was that one of the services of directory. The CCITT created standard X.500 in 1988, than divenne 9594 ISO Date Communications Network Directory Recommendations X.500-X.521 in 1990.
According to this standard, the communication between directory client and serveur use Directory Access Protocol (DAP). But for operating being, the DAP demands the entire battery DARES, since is a protocol of the level applications.
These two processes of standardization face the problem from two perspective different. The approach DARES begins from zero and defines standard using a formal model without to demand implementazioni. Internet uses a less formal approach, where anyone can propose and to comment RFC that comes then implements to you in order to verify of the feasibility. The protocols DARE are develop to you slowly, especially in the market of personal the computers. To contrary TCP/IP and Internet they have had a greater application and they are develops to you quickly. Some companies developed therefore to the own protocols and products for the network. In any case the protocols DARE had importance in the large distributed systems that they were being developed in particular way. An important area was that one of the services of directory. The CCITT created standard X.500 in 1988, than divenne 9594 ISO Date Communications Network Directory Recommendations X.500-X.521 in 1990.
According to this standard, the communication between directory client and serveur use Directory Access Protocol (DAP). But for operating being, the DAP demands the entire battery DARES, since is a protocol of the level applications.
Telnet Guide
Client the telnet still is used occasionally in order "to speak" to other services. Telnet is used every as well as in the debug of services of networking like server smtp and HTTP, in how much it represents a way simple in order to send commandos to the server and to examine the answers. Telnet can also be used like a rudimentale client IRC if one is possessed adequate acquaintance.
Telnet is a lot used for the games User Fines Dungeon plays to you in net.
In the field of E-mail telnet it has many valid uses, as an example is possible to read the correspondence on the own one mailbox, to cancel it or to send electronic missive. Approval that normally the access alla own case of e-mail comes made in not sure way or to times from a public Computer, the problems of emergency of telnet are not of obstacle.
To times with the Webmail problems of access to own mailbox that with telnet they can be resolved, as an example in the case of overcoming of the granted memory the some cases are had jam and telnet allows to resolve the problem.
Other particular interesting of telnet and e-mail it is the possibility of anonymous shipment of false email or email (fake email). If they do not come it uses you proxy the magistracy through the police mail them is in a position to characterizing the sender through its IP address.
Telnet can be used from a common one browser web, in presence of one logon (generally HTTP) already active to an Internet Service Provider: Telnet is a protocol of level higher than those of the level of transport of the data, and demands that a session already is begun.
Telnet is a lot used for the games User Fines Dungeon plays to you in net.
In the field of E-mail telnet it has many valid uses, as an example is possible to read the correspondence on the own one mailbox, to cancel it or to send electronic missive. Approval that normally the access alla own case of e-mail comes made in not sure way or to times from a public Computer, the problems of emergency of telnet are not of obstacle.
To times with the Webmail problems of access to own mailbox that with telnet they can be resolved, as an example in the case of overcoming of the granted memory the some cases are had jam and telnet allows to resolve the problem.
Other particular interesting of telnet and e-mail it is the possibility of anonymous shipment of false email or email (fake email). If they do not come it uses you proxy the magistracy through the police mail them is in a position to characterizing the sender through its IP address.
Telnet can be used from a common one browser web, in presence of one logon (generally HTTP) already active to an Internet Service Provider: Telnet is a protocol of level higher than those of the level of transport of the data, and demands that a session already is begun.
Details of the Telnet protocol
Telnet is a client-serveur protocol based on TCP; the client usually they are connected to door 23 on the serveur (in spite of the door can be different, like for several Internet protocols). In part because of the planning of the protocol and in part for the flexibility typically supplied from programs telnet, is possible to use a program telnet in order to establish one interactive logon to some other service on a serveur Internet. I use classic is to be connected with the telnet to door 25 (on which typically a serveur smtp is found ) in order to carry out the debugging of a mail serveur.
Protocol telnet can be divided in a main part and a set of extensions. The main part is described from 854 RFC and RFC 855 of the IETF, that also they are joined in STD 8, and defines the characteristics base of the protocol and the way to implement the extensions. Between the many extensions, some have been adopted like Internet Standard. Documents STD from the 27 to the 32 define several extensions of telnet, the greater part di.le which are much diffuse. Between the remaining extensions, the more important are those proposals from the IETF like standard; ulterior details can are find to you in STD 1.
Like explained more ahead, telnet is not sure and would have generally is avoided. Its use on the freenets involves serious risks of emergency.
Protocol telnet can be divided in a main part and a set of extensions. The main part is described from 854 RFC and RFC 855 of the IETF, that also they are joined in STD 8, and defines the characteristics base of the protocol and the way to implement the extensions. Between the many extensions, some have been adopted like Internet Standard. Documents STD from the 27 to the 32 define several extensions of telnet, the greater part di.le which are much diffuse. Between the remaining extensions, the more important are those proposals from the IETF like standard; ulterior details can are find to you in STD 1.
Like explained more ahead, telnet is not sure and would have generally is avoided. Its use on the freenets involves serious risks of emergency.
Telnet
Telnet is a protocol of net used on Internet. Documents IETF STD 8 (RFC 854 and RFC 855) say:
The objective of protocol telnet is to supply a support for the communications sufficiently generalized, bidirectional and oriented to the byte (eight bit).
Usually it is used in order to supply to the remote customer sessions of login of type line of commando between host on Internet.
By extension, telnet it is also the name of a program that a customer can use in order to start one session telnet to a remote host; the program telnet implements the part client of the protocol. Client the telnet has been available on the greater part of the Unix systems for several years and is available for whichever type of computer.
In English to telnet it is used like verbo and it means to establish one logon telnet.
The objective of protocol telnet is to supply a support for the communications sufficiently generalized, bidirectional and oriented to the byte (eight bit).
Usually it is used in order to supply to the remote customer sessions of login of type line of commando between host on Internet.
By extension, telnet it is also the name of a program that a customer can use in order to start one session telnet to a remote host; the program telnet implements the part client of the protocol. Client the telnet has been available on the greater part of the Unix systems for several years and is available for whichever type of computer.
In English to telnet it is used like verbo and it means to establish one logon telnet.
Authentication of the Server
SSH previews also the verification of the authenticity of the server. This serves to avoid that a malignant customer "impersoni" the serveur, making itself to supply the credentials of the customer (attack man in the middle). For this purpose, for every serveur brace of asymmetric keys comes generated one. The private key remains on the serveur. The public key must be installed on the client. When a client it is connected to a serveur of which it knows the public key, verification that the serveur is still in possession of the private key. If this verification fails, the logon comes inclination to leeward, avoiding to supply credentials to the serveur.
In the practical one, when it is connected to us to a serveur for before the time, the client it asks if the public key of this serveur is wanted to be accepted, and if the customer answers positively memorizza this key and it continues in the logon. To the successive logons with the same serveur, client of the verification the authenticity, and in case the private key does not correspond prevents to continue the logon.
In the practical one, when it is connected to us to a serveur for before the time, the client it asks if the public key of this serveur is wanted to be accepted, and if the customer answers positively memorizza this key and it continues in the logon. To the successive logons with the same serveur, client of the verification the authenticity, and in case the private key does not correspond prevents to continue the logon.
Mechanisms of authentication of the client
Mainly two methods of authentication exist in order to control the access to a serveur ssh:
username/password
The customer supplies a name customer and a password, that they come validated from the serveur. This exchange happens to the inside of a number channel, for which it is not to interception risk.
Procedure:
1. To ==> B: SSH_MSG_USERAUTH_REQUEST, pappy, ssh-userauth, keyboard-interactive
2. B ==> To: SSH_MSG_USERAUTH_INFO_REQUEST, pappy, password-authentication, 1, "Enter Password"
3. To ==> B: SSH_MSG_USERAUTH_INFO_RESPONSE, 1, "love"
4. B ==> To: SSH_MSG_USERAUTH_SUCCESS.
public key
This method of authentication is based on the asymmetric cryptography. In order to use it the customer brace of keys generates one. The public key is copied on the serveur, typically in appropriate rows in the home directory of the customer; the private key must be conserved from the customer, and is well that word is protect with one key (passphrase).
In the phase of access, client ssh the test to the serveur of being in possession of the private key, and in succeeding case of comes concurred the access. In this way, to the customer it is not demanded to supply the own one password to every logon.
username/password
The customer supplies a name customer and a password, that they come validated from the serveur. This exchange happens to the inside of a number channel, for which it is not to interception risk.
Procedure:
1. To ==> B: SSH_MSG_USERAUTH_REQUEST, pappy, ssh-userauth, keyboard-interactive
2. B ==> To: SSH_MSG_USERAUTH_INFO_REQUEST, pappy, password-authentication, 1, "Enter Password"
3. To ==> B: SSH_MSG_USERAUTH_INFO_RESPONSE, 1, "love"
4. B ==> To: SSH_MSG_USERAUTH_SUCCESS.
public key
This method of authentication is based on the asymmetric cryptography. In order to use it the customer brace of keys generates one. The public key is copied on the serveur, typically in appropriate rows in the home directory of the customer; the private key must be conserved from the customer, and is well that word is protect with one key (passphrase).
In the phase of access, client ssh the test to the serveur of being in possession of the private key, and in succeeding case of comes concurred the access. In this way, to the customer it is not demanded to supply the own one password to every logon.
Example of use of the port forwarding
Sure between a door of client and a door of the remote serveur or whichever third machine behind the sever remote, on condition that but the port forwarding it is useful as an example in order to make attendance remote to blots some lacking in a sure system of remote management. It is possible to create a tunnel knows SERVEUR SSH has qualified the forwarding. This is normally possible without to install no additional package.
X forwarding
The port forwarding logon SSH is useful also in order to transport applications X Window through one. SSH automatically sets up also opportune the variable ones of atmosphere, so that applications X launch from one finish them remote come visualized on the display from which it has been started the logon.
The X forwarding from the side client it must be qualified passing option "- X" while from the serveur side it goes modified the configuration rows /etc/ssh/sshd_config qualifying the directive X11Forwarding (you remember yourselves of riavviare the serveur once brought the modification to the configuration rows).
The X forwarding from the side client it must be qualified passing option "- X" while from the serveur side it goes modified the configuration rows /etc/ssh/sshd_config qualifying the directive X11Forwarding (you remember yourselves of riavviare the serveur once brought the modification to the configuration rows).
Port forwarding
SSH allows to realize of the tunnels cripta you, that they allow to transport arbitrary sessions TCP to the inside of the criptata logon, allowing protect from interception not sure protocols, or to go around limitations of routing.
This functionality is said port forwarding, and allows to open one socket TCP on client the SSH (local port forwarding) or on the serveur (remote port forwarding). The logons received on this door come forwarded from the other head of logon SSH, towards a host and one specific door.
As an example, with this commando it is connected to us to host1, forwarding the door 10022> of the machine in which we launch the client ssh to door 22 of host2 through a sure channel between client and host1
ssh host1 - L 10022:host2:22
This functionality is said port forwarding, and allows to open one socket TCP on client the SSH (local port forwarding) or on the serveur (remote port forwarding). The logons received on this door come forwarded from the other head of logon SSH, towards a host and one specific door.
As an example, with this commando it is connected to us to host1, forwarding the door 10022> of the machine in which we launch the client ssh to door 22 of host2 through a sure channel between client and host1
ssh host1 - L 10022:host2:22
Secure shell
SSH (Secure SHell, shell sure) is a protocol that allows to establish one number remote session to interface to line of commando with an other host.
Client the SSH has an interface to line of commando similar to that one of telnet and rlogin, but the entire communication (that is is the authentication that the job session) happens in number way. For this reason, SSH has become a standard of fact for the remote administration of systems unix and dispositi you of net, rendering obsolete the protocol telnet, too much dangerous sentence for its lack of protection against the interceptions.
Client and serveur SSH is installs to you or installabili on many versions of UNIX, Linux, Mac OS X and Microsoft Windows. Moreover it is available as administration instrument on some apparatuses of net
Client the SSH has an interface to line of commando similar to that one of telnet and rlogin, but the entire communication (that is is the authentication that the job session) happens in number way. For this reason, SSH has become a standard of fact for the remote administration of systems unix and dispositi you of net, rendering obsolete the protocol telnet, too much dangerous sentence for its lack of protection against the interceptions.
Client and serveur SSH is installs to you or installabili on many versions of UNIX, Linux, Mac OS X and Microsoft Windows. Moreover it is available as administration instrument on some apparatuses of net
The emergency of protocol smtp
One of the limitations of original protocol smtp is that it does not managethe authentication of the senders. Beyond to the Spam risk, the possibility exists to send email making to appear like sender the address correspondent to an other account. Without to approach the account of thirds party, logon to the mail-serveur is possible to establish one and to write containing a coded message smtp the relative commandos you to sender and adressee, to give to the relati to you parameters and the body of the email.
In order to obviate to these problems it has been developed a called extension SMTP-AUTH.
Although this, the Spam remains a serious problem still today. However, a radical review of protocol smtp is not thought practicable, for via of the great number of implementazioni of the protocol puts into effect them as an example (, has been proposed Internet Mail 2000 like alternative protocol).
For this reason auxiliary protocols have been various proposals in order to assist transactions smtp.The Anti-Spam Research Group ofthe IRTF is working on several proposals of authentication email centered on the flexibility, lightness and scalabilità.
In order to obviate to these problems it has been developed a called extension SMTP-AUTH.
Although this, the Spam remains a serious problem still today. However, a radical review of protocol smtp is not thought practicable, for via of the great number of implementazioni of the protocol puts into effect them as an example (, has been proposed Internet Mail 2000 like alternative protocol).
For this reason auxiliary protocols have been various proposals in order to assist transactions smtp.The Anti-Spam Research Group ofthe IRTF is working on several proposals of authentication email centered on the flexibility, lightness and scalabilità.
Smtp
Simple Mail Transfer Protocol (smtp) is the protocol standard for the transmission via email Internet . In Italian it could be translate like "elementary Protocol of transfer mails them".
It is a relatively simple, testuale protocol, in which they come specifies or more adressees to you than a message, verified their existence, the message comes transferred. It is enough easy to verify like works a serveur smtp by means of client a telnet. The smtp uses the protocol of transmission TCP and, in order to approach to you, door 25. In order to associate serveur smtp to a data name of dominion (DNS) a called record MX (Mail Exchange is used).
The smtp began to diffuse itself in first years ' 80. To that time it was an alternative tothe UUCP, that more it was adapted to manage the transfer of email between computer whose logon was intermittent. The smtp, of other part, works better if the computers are always connect you to the net.
Sendmail was one of first (if not just the first) mail transfer agent to implement protocol smtp. Until the 2001 they have been at least written 50 programs that implement protocol smtp like client (sender of the messages) or serveur (adressee of the message). Other serveur much diffuse is Exim di Philip Hazel, Postfix di Wietse Venema, qmail of D. J. Bernstein, Courier di Sam Varshavchik and Microsoft Exchange Serveur.
Since smtp is a testuale protocol based on codifies ASCII, it is not allowed to directly transmit to text composed with a various character set and tantomeno binary rows. Standard MIME allows to extend the format of the messages maintaining the compatibility with the existing software. As an example, to the day today much serveur smtp supports extension 8BITMIME, which allows a transfer of a text that contains accented characters (non-ASCII) without need of trascodificarlo. Other limits of smtp, which the maximum length of a line, prevents the shipment of binary rows without trascodifica. (Famous that for the binary rows it sendes to you with HTTP it uses format MIME without need of one trascodifica.)
The smtp is a protocol that only allows to send mail messages, but not to demand them to a serveur: in order to make this the client of mail it must use other protocols, which the POP3, or Post Office Protocol,the IMAP, or Internet Message Access Protocol.
It is a relatively simple, testuale protocol, in which they come specifies or more adressees to you than a message, verified their existence, the message comes transferred. It is enough easy to verify like works a serveur smtp by means of client a telnet. The smtp uses the protocol of transmission TCP and, in order to approach to you, door 25. In order to associate serveur smtp to a data name of dominion (DNS) a called record MX (Mail Exchange is used).
The smtp began to diffuse itself in first years ' 80. To that time it was an alternative tothe UUCP, that more it was adapted to manage the transfer of email between computer whose logon was intermittent. The smtp, of other part, works better if the computers are always connect you to the net.
Sendmail was one of first (if not just the first) mail transfer agent to implement protocol smtp. Until the 2001 they have been at least written 50 programs that implement protocol smtp like client (sender of the messages) or serveur (adressee of the message). Other serveur much diffuse is Exim di Philip Hazel, Postfix di Wietse Venema, qmail of D. J. Bernstein, Courier di Sam Varshavchik and Microsoft Exchange Serveur.
Since smtp is a testuale protocol based on codifies ASCII, it is not allowed to directly transmit to text composed with a various character set and tantomeno binary rows. Standard MIME allows to extend the format of the messages maintaining the compatibility with the existing software. As an example, to the day today much serveur smtp supports extension 8BITMIME, which allows a transfer of a text that contains accented characters (non-ASCII) without need of trascodificarlo. Other limits of smtp, which the maximum length of a line, prevents the shipment of binary rows without trascodifica. (Famous that for the binary rows it sendes to you with HTTP it uses format MIME without need of one trascodifica.)
The smtp is a protocol that only allows to send mail messages, but not to demand them to a serveur: in order to make this the client of mail it must use other protocols, which the POP3, or Post Office Protocol,the IMAP, or Internet Message Access Protocol.
Post Office Protocol
The Post Office Protocol (said also POP) is a protocol that has the task to allow, by means of authentication, the access to a account of present e-mail on a host in order to unload the email of the relative one account. Demon POP (in version 3) remains in attended on door 110 of the host (of default, but logon TCP from part of a client can also be various) for one. The e-mail messages, for being read, must be unload on the computer (this to you are a remarkable difference regardingthe IMAP), even if are possible to leave of one copy on the host. Protocol POP3 does not preview some type of coding, therefore the password used for the authentication between serveur and client pass in luminosity. In order to resolve this possible problem it has been developed extension APOP that uses MD5.
IMAP
The IMAP (Internet Message Access Protocol or Interactive Mail Access Protocol) is a protocol of communication for the email reception . The meant "Interactive Mail Access Protocol" has been valid until version 3, from the quarter in then is changed in "Internet Message Access Protocol". It puts into effect them version is "4 revision 1".
The protocol has been invented from Mark Crispin in 1986 [ 1 ] like more modern alternative to utilizzatissimo the POP. Both allow to a client to approach, to read and to cancel the email from a serveur, but with some differences. Here a directory of the characteristics of the IMAP but not of the POP:
* Access to the mail is online that off-linens
While the POP3 is used, the client it is connected in order to unload the new messages and then it is d3connectered. With the IMAP the client it remains connected and it answers to the demands that the customer makes through the interface; this allows to save time if there are messages of great dimensions.
* More customers can use the same case of mail
Protocol POP assumes that a solo client (customer) is connected to one determined mailbox (mail case), that one that it has been assigned. To the contrary the IMAP4 allows simultaneous logons the same one mailbox, supplying mechanisms in order to control the changes brings to you from every customer.
* Support to the access to single parts MIME of a message
The greater part of the email is transmitted in format MIME, that it allows a tree structure of the message, where every branch is a various content (headings, encloses or parts of it, message in a formed data, etc to you). Protocol IMAP4 allows to unload a single part MIME or quite sections of the parts, for having a preview of the message or in order to unload a mail without the rows enclose to you.
* Support for attributes of the messages held from the serveur.
Through the use of attributes, held on the serveur, defined in protocol IMAP4, every single client it can hold trace of every message, as an example for knowing if already it has been read or if answer has had one.
* Case access multiple of mail on the serveur
Some customers, with protocol IMAP4, can create, modify or cancel mailbox (of usual associated to cartelle) on the serveur. Moreover, this management of the mailbox, allows cartelle to have shared between various customers.
* Possibility to make searches on the serveur
The IMAP4 allows the client to ask the serveur which messages satisfies a sure criterion, in order to make, as an example, of the searches on the messages without having to unload them all.
* Support of a mechanism for the definition of extensions
In the detailed lists of the IMAP it is described like a serveur can make to know the customers if it has of the extra functionalities. Many extensions of the IMAP are much diffuse.
* Password criptate
With protocol POP the password they usually come sended in text, rendering easy, with one interception, the location of the password. With the IMAP it is possible criptare the password, even if serveur and client must find an agreement on the method.
The IMAP mainly is used in great network like university or companies, where a customer often changes emplacement: with the POP3, time would be necessary to unload the messages every that changes PC, while with the IMAP they can be only unloaded the new messages or be approached to a specific message without having to unload the others
The door predefined of demon IMAP onthe host is the 143. If a sure logon through SSL is used , then the door is the 993.
The protocol has been invented from Mark Crispin in 1986 [ 1 ] like more modern alternative to utilizzatissimo the POP. Both allow to a client to approach, to read and to cancel the email from a serveur, but with some differences. Here a directory of the characteristics of the IMAP but not of the POP:
* Access to the mail is online that off-linens
While the POP3 is used, the client it is connected in order to unload the new messages and then it is d3connectered. With the IMAP the client it remains connected and it answers to the demands that the customer makes through the interface; this allows to save time if there are messages of great dimensions.
* More customers can use the same case of mail
Protocol POP assumes that a solo client (customer) is connected to one determined mailbox (mail case), that one that it has been assigned. To the contrary the IMAP4 allows simultaneous logons the same one mailbox, supplying mechanisms in order to control the changes brings to you from every customer.
* Support to the access to single parts MIME of a message
The greater part of the email is transmitted in format MIME, that it allows a tree structure of the message, where every branch is a various content (headings, encloses or parts of it, message in a formed data, etc to you). Protocol IMAP4 allows to unload a single part MIME or quite sections of the parts, for having a preview of the message or in order to unload a mail without the rows enclose to you.
* Support for attributes of the messages held from the serveur.
Through the use of attributes, held on the serveur, defined in protocol IMAP4, every single client it can hold trace of every message, as an example for knowing if already it has been read or if answer has had one.
* Case access multiple of mail on the serveur
Some customers, with protocol IMAP4, can create, modify or cancel mailbox (of usual associated to cartelle) on the serveur. Moreover, this management of the mailbox, allows cartelle to have shared between various customers.
* Possibility to make searches on the serveur
The IMAP4 allows the client to ask the serveur which messages satisfies a sure criterion, in order to make, as an example, of the searches on the messages without having to unload them all.
* Support of a mechanism for the definition of extensions
In the detailed lists of the IMAP it is described like a serveur can make to know the customers if it has of the extra functionalities. Many extensions of the IMAP are much diffuse.
* Password criptate
With protocol POP the password they usually come sended in text, rendering easy, with one interception, the location of the password. With the IMAP it is possible criptare the password, even if serveur and client must find an agreement on the method.
The IMAP mainly is used in great network like university or companies, where a customer often changes emplacement: with the POP3, time would be necessary to unload the messages every that changes PC, while with the IMAP they can be only unloaded the new messages or be approached to a specific message without having to unload the others
The door predefined of demon IMAP onthe host is the 143. If a sure logon through SSL is used , then the door is the 993.
Network News Transfer Protocol
The Network News Transport Protocol, often abbreviated like NNTP, is the protocol used from the service Internet Usenet, whose common application is the so-called the Newsgroup. Bit is a protocol TCP/IP based on stringhe of text sent on 7 channels TCP ASCII to.
It is used mainly in the software it develops to you for the serveur, in order to manage the transfer of articles between of they, and is also to the base of protocol NNRP (Network News Reader Protocol), used from the software of the client in order to connect itself to the serveur.
It is used mainly in the software it develops to you for the serveur, in order to manage the transfer of articles between of they, and is also to the base of protocol NNRP (Network News Reader Protocol), used from the software of the client in order to connect itself to the serveur.
Ftp
The ftp, acronym of File Transfer Protocol (transfer protocol rows), is a service that supplies the fundamental elements for the sharing of rows between host.
It objects you of the ftp are:
1. to promote the sharing of rows (programs or data)
2. to encourage the indirect or implicit use (through program) of remote computers
3. to safeguard the customer to varying of the stoccaggio systems rows, between a host and the other
4. to transfer given in reliable and efficient way
The ftp has endured one long evolution in the years: the first mechanism of transmission rows laughed them to 1971, was developed near the MIT.
It objects you of the ftp are:
1. to promote the sharing of rows (programs or data)
2. to encourage the indirect or implicit use (through program) of remote computers
3. to safeguard the customer to varying of the stoccaggio systems rows, between a host and the other
4. to transfer given in reliable and efficient way
The ftp has endured one long evolution in the years: the first mechanism of transmission rows laughed them to 1971, was developed near the MIT.
the IRC slang
On IRC often it can capitare of imbattersi in acronyms used in substitution of made phrases, most times in English but not necessarily:
* ircwar - series of actions carried out from malintenzionati with the scope to ruin the tranquillity of the net
* takeover - typical action ofthe ircwar through which a customer takes the control of a channel; impossible to the inside of the network that they implement a management service channels (chanserv);
* nuke - any type of attack in a position to d3connectering a customer from serveur IRC
* ROTFL - Rolling On the Floor Laughing ("... I am rolling myself on the pavement from the risate ones")
* RTFM - Read The F * Manual ("goes to read the f to you * manual")
* ASAP - As Soon As Possible ("how much before")
* KING - REturned ("has re-entered")
* BTW - By The Way ("in any case")
* AFAIK - As Far As the Know ("to the best of my knowledge and belief")
* BRB - Be Right Back ("endured return")
* KISS - Keep It Short, Simple! ("it makes it short and simple!")
* LOL - Laughing Out Loud (risata to high voice)
* AFK - Away From keyboard (not to the computer)
* FYI - For Your Information (for your information)
* IMO - In My Opinion ("second me")
* IMHO - In My Humble Opinion ("according to my modest one to seem")
* STFU - Shut The Fuck Up. ("you close the spout")
* BYOB - Bring Your Own Beer. ("door your beer")
* AKA - Also Known As. ("known also like")
* ASL - Age Sex Location. ("Age sex locality")
* LMAO - Laughing My Ass Off. ("I crack myself from the risate ones")
* IRL - In Real Life. ("in the true life")
* {P} - ("Kiss with the language - Used in the Bg slang of mIRC (IRC)")
* ircwar - series of actions carried out from malintenzionati with the scope to ruin the tranquillity of the net
* takeover - typical action ofthe ircwar through which a customer takes the control of a channel; impossible to the inside of the network that they implement a management service channels (chanserv);
* nuke - any type of attack in a position to d3connectering a customer from serveur IRC
* ROTFL - Rolling On the Floor Laughing ("... I am rolling myself on the pavement from the risate ones")
* RTFM - Read The F * Manual ("goes to read the f to you * manual")
* ASAP - As Soon As Possible ("how much before")
* KING - REturned ("has re-entered")
* BTW - By The Way ("in any case")
* AFAIK - As Far As the Know ("to the best of my knowledge and belief")
* BRB - Be Right Back ("endured return")
* KISS - Keep It Short, Simple! ("it makes it short and simple!")
* LOL - Laughing Out Loud (risata to high voice)
* AFK - Away From keyboard (not to the computer)
* FYI - For Your Information (for your information)
* IMO - In My Opinion ("second me")
* IMHO - In My Humble Opinion ("according to my modest one to seem")
* STFU - Shut The Fuck Up. ("you close the spout")
* BYOB - Bring Your Own Beer. ("door your beer")
* AKA - Also Known As. ("known also like")
* ASL - Age Sex Location. ("Age sex locality")
* LMAO - Laughing My Ass Off. ("I crack myself from the risate ones")
* IRL - In Real Life. ("in the true life")
* {P} - ("Kiss with the language - Used in the Bg slang of mIRC (IRC)")
Client IRC
* Multiple Platforms: ChatZilla, Pidgin, jIRC, XChat, KVIrc,
irssi
* Microsoft Windows: Bersirc, dIRC, HydraIRC, Klient, mIRC, pIRCh, Trillian, vIRC, XiRCON, Miranda IM, Microsoft Comic Chat (being mIRC most popular between the IRC).
* Unix(- like): BitchX, epic, IIRC, ircII, WeeChat, Kopete, KVIrc, XChat, TalkSoup (GNUstep), Zircon, Konversation (KDE)
* Mac OS: X-Chat Aqua, Fire, IRCle, Minerva, Snak, ShadowIRC, Colloquy, MacIrssi
* AmigaOS: AmIRC
Nets IRC have given place to the creation of "client automati to us" call to you "bot", abbreviation of "robot". The first one "bot" was written from Greg Lindahl and served from automated moderator for the Wumpus game.
Those most recent ones (between all eggdrop) instead are used in order to automate the moderation of the channels in the unprovided nets of services IRC (like NickServ, ChanServ and other implementazioni) even if are often only of annoyance to the customers (beyond that for the serveur who find again a greater cargo of customers to manage). They are usually develops in Java language and allow a standard to you of functionalities that space from the shipment of private messages to the email of not connected customers, R-all'.apertura of chat room private with customers online, to the shipment of emoticon to the inside of the messages.
An ulterior evolution in field of "bot" is sure the advent of psotnic, a bot whose speeds are by far advanced to those of a eggdrop. Anch' it is equipped of partyline, shipment private messages and expansions with script in c.
irssi
* Microsoft Windows: Bersirc, dIRC, HydraIRC, Klient, mIRC, pIRCh, Trillian, vIRC, XiRCON, Miranda IM, Microsoft Comic Chat (being mIRC most popular between the IRC).
* Unix(- like): BitchX, epic, IIRC, ircII, WeeChat, Kopete, KVIrc, XChat, TalkSoup (GNUstep), Zircon, Konversation (KDE)
* Mac OS: X-Chat Aqua, Fire, IRCle, Minerva, Snak, ShadowIRC, Colloquy, MacIrssi
* AmigaOS: AmIRC
Nets IRC have given place to the creation of "client automati to us" call to you "bot", abbreviation of "robot". The first one "bot" was written from Greg Lindahl and served from automated moderator for the Wumpus game.
Those most recent ones (between all eggdrop) instead are used in order to automate the moderation of the channels in the unprovided nets of services IRC (like NickServ, ChanServ and other implementazioni) even if are often only of annoyance to the customers (beyond that for the serveur who find again a greater cargo of customers to manage). They are usually develops in Java language and allow a standard to you of functionalities that space from the shipment of private messages to the email of not connected customers, R-all'.apertura of chat room private with customers online, to the shipment of emoticon to the inside of the messages.
An ulterior evolution in field of "bot" is sure the advent of psotnic, a bot whose speeds are by far advanced to those of a eggdrop. Anch' it is equipped of partyline, shipment private messages and expansions with script in c.
Internet Relay Chat technical Information
RFC 1459 describes the protocols uses you and more recently IRC2 with RFC 2810, RFC 2811, 2812 RFC and RFC 2813 describe with of proposals of extensions to model IRC. Many implementazioni IRC consist in protocol IRC2 with several add-on that they prevent the incompatibilità caused of the differences between the software uses you for the management of the net serveur.
IRC is an open protocol of net that uses the protocol of transmission TCP optionally (Transmission Control Protocol) andthe SSL (Secure Sockets Layer). A serveur IRC (called IRCd) is in a position to connecting with other serveur IRC forming therefore one true and own net of communication; the customers approach to it by means of the logon of a client to a serveur. Much serveur IRC does not demand the customer to authenticate itself, but it goes however specified a nickname (univoco to level of net IRC).
IRC is a protocol plaintext, this means that it is possible (however with some disadvantage) to use it through one type logon socket raw. However not there is way to define the character of decodes goddesses messages and goddesses nickname rendering the filtering of characters not ASCIIimpossible.
The fundamental mass media in a session IRC is the "channel", a group of customers identified from a name, where all the pertaining can only send leggibili messages from the customers of the same group. A channel IRC is created automatically to the first income from part of whichever customer.
The names of the channels pertaining to all an entire net IRC are identified with the character "#" begin them, while those premises (specific of a serveur) are identify with the character "&" (however this last one to you could not be available on some nets). In order to obviate to problems of desincronizzazione of the channels in the moment in which of the serveur they had been scollegati the channels were created "!" without the sincronismo problems that but the customers obtained insufficient succeeding also for the lack of information.
The first customer who enters in a channel acquires automatically of privileges that other present customer in the same channel can then pass to whichever; these customers come call to you channel operator or, in channel Italian"operating". There are also various customers with privileges different and with tasks of administration of the network; these are call IRC to you Operator (abbreviated in IRCop, often erroneously confused in IR-Cop) or operating Italian "IRC". In the more recent implementazioni it is also possible to record the channels, so that the access rights do not come lost to the logoff of the last operator; where this is not possible comes made use of bot, special programs that appear like normal customers, but that they garrison the channel and, to the use, river-they confer the status of operator to the owners.
The "Operating ones of the channel" can set up various options on that determined channel, see b:IRC/Modi_canale.
The customers in the within of the channel or the serveur can have various attributes, see b:IRC/Modi_utente
Logons IRC are a ghiotto objective for cracker malintenzionati, in how much, also being number, take, for they same nature, long periods of time of logon. It is necessary therefore to assure to these logons, one taken care of political of emergency in a position to proteggerle from the script attacks kiddie that try to take of control (IRC takeover war), even trying than to take advantage of just advantage a netsplit (as the split is said in jargon riding).
Logon IRC often comes used from part of the scripts kiddies like "laboratory" in order to try various types of attacks in net, as an example sending to packages ICMP (Internet Control Message Protocol) badly forms you to the aim to disturb of the customers (sees also nuke. However, with the entrance in scene of Bouncer (BNC) and virtual the hosts, an attack is much difficult one for these malintenzionate persons to carry a.termine, inasmuch as these services succeed to hide IP address connected to a nickname.
IRC is an open protocol of net that uses the protocol of transmission TCP optionally (Transmission Control Protocol) andthe SSL (Secure Sockets Layer). A serveur IRC (called IRCd) is in a position to connecting with other serveur IRC forming therefore one true and own net of communication; the customers approach to it by means of the logon of a client to a serveur. Much serveur IRC does not demand the customer to authenticate itself, but it goes however specified a nickname (univoco to level of net IRC).
IRC is a protocol plaintext, this means that it is possible (however with some disadvantage) to use it through one type logon socket raw. However not there is way to define the character of decodes goddesses messages and goddesses nickname rendering the filtering of characters not ASCIIimpossible.
The fundamental mass media in a session IRC is the "channel", a group of customers identified from a name, where all the pertaining can only send leggibili messages from the customers of the same group. A channel IRC is created automatically to the first income from part of whichever customer.
The names of the channels pertaining to all an entire net IRC are identified with the character "#" begin them, while those premises (specific of a serveur) are identify with the character "&" (however this last one to you could not be available on some nets). In order to obviate to problems of desincronizzazione of the channels in the moment in which of the serveur they had been scollegati the channels were created "!" without the sincronismo problems that but the customers obtained insufficient succeeding also for the lack of information.
The first customer who enters in a channel acquires automatically of privileges that other present customer in the same channel can then pass to whichever; these customers come call to you channel operator or, in channel Italian"operating". There are also various customers with privileges different and with tasks of administration of the network; these are call IRC to you Operator (abbreviated in IRCop, often erroneously confused in IR-Cop) or operating Italian "IRC". In the more recent implementazioni it is also possible to record the channels, so that the access rights do not come lost to the logoff of the last operator; where this is not possible comes made use of bot, special programs that appear like normal customers, but that they garrison the channel and, to the use, river-they confer the status of operator to the owners.
The "Operating ones of the channel" can set up various options on that determined channel, see b:IRC/Modi_canale.
The customers in the within of the channel or the serveur can have various attributes, see b:IRC/Modi_utente
Logons IRC are a ghiotto objective for cracker malintenzionati, in how much, also being number, take, for they same nature, long periods of time of logon. It is necessary therefore to assure to these logons, one taken care of political of emergency in a position to proteggerle from the script attacks kiddie that try to take of control (IRC takeover war), even trying than to take advantage of just advantage a netsplit (as the split is said in jargon riding).
Logon IRC often comes used from part of the scripts kiddies like "laboratory" in order to try various types of attacks in net, as an example sending to packages ICMP (Internet Control Message Protocol) badly forms you to the aim to disturb of the customers (sees also nuke. However, with the entrance in scene of Bouncer (BNC) and virtual the hosts, an attack is much difficult one for these malintenzionate persons to carry a.termine, inasmuch as these services succeed to hide IP address connected to a nickname.
Internet Relay Chat
Internet Relay Chat (IRC) has been before the shape of instantaneous communication (chat) on Internet. It concurs is the communication directed between two customers who the contemporeaneo dialogue of entire groups in "rooms" of argument calls "channels".
Gnutella
Gnutella is one net Peer to Peer of open sharing of rows.
The protocols of which it is composed are opened publics and. Its main function is the search of rows to the inside of the nodes of the same net, and the successive transfer of the same ones to the petitioner.
The first implementazione of the protocol has been the Gnutella program written from Justin Frankel and Tom Pepper for the Nullsoft to the beginning of 2000. The program was distributed a single day, 14 March 2000 and was unloaded from migliaia of persons, thanks to the announcement appeared on Slashdot. The code would have been rilasciato later on probably under licenda GNU GPL. The day after AOL, that it had from little acquired the Nullsoft, bloccò the distribution of the program for reasons lawyers and diffidò the Nullsoft continuing some the development. Although this the net gnutella survived supported from migliaia of unloaded copies the first day that continued to distribute the program. In little days then the protocol was reingegnerizzato and nacquero new free programs in a position to approaching this net.
Although the name contains word GNU, it is not part of plan GNU, for this reason the FSF, caretaker of plan GNU, of it has asked the change of the name. The second part of the name derives from the Nutella, a lot appreciated from the sviluppatori of this net.
Gnutella is a typical example of overlay network.
The protocols of which it is composed are opened publics and. Its main function is the search of rows to the inside of the nodes of the same net, and the successive transfer of the same ones to the petitioner.
The first implementazione of the protocol has been the Gnutella program written from Justin Frankel and Tom Pepper for the Nullsoft to the beginning of 2000. The program was distributed a single day, 14 March 2000 and was unloaded from migliaia of persons, thanks to the announcement appeared on Slashdot. The code would have been rilasciato later on probably under licenda GNU GPL. The day after AOL, that it had from little acquired the Nullsoft, bloccò the distribution of the program for reasons lawyers and diffidò the Nullsoft continuing some the development. Although this the net gnutella survived supported from migliaia of unloaded copies the first day that continued to distribute the program. In little days then the protocol was reingegnerizzato and nacquero new free programs in a position to approaching this net.
Although the name contains word GNU, it is not part of plan GNU, for this reason the FSF, caretaker of plan GNU, of it has asked the change of the name. The second part of the name derives from the Nutella, a lot appreciated from the sviluppatori of this net.
Gnutella is a typical example of overlay network.
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