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Linda J. Seamonson
Eric C. Rosen
BBN Communications
January 1984
"Cotta" external gateway agreement
(RFC888 - "stub" exterior Gateway Protocol)
The external gateway protocols set forth in this note are used to tell a cigarette network to associate with a core gateway of a self-government system. Text
The work agreement is set up and defines an ARPA official agreement. All gateways have written this should read carefully
This article.
table of Contents
1 Introduction 1
2. Definition and Introduction 2
3. Neighbor
4. Neighbor Dredable Agreement 3
5. Network Can Deta (NR) Packet 4
6. NR packet polling technology 6
7. Send NR packet 6
8. Indirect neighbor 7
9. Limitations 7
1 Introduction
Darpa catenet has a hopes to become an expanded system, because there are more and more networks more and more
The host continues to join. Of course this requires more gateways. In the past, this extension was in a relatively non-organized form.
Row. The new gateway, usually contains software that is extremely different from the existing gateway, which will continue to increase and immediately pass the EGP protocol.
Participate in the common routing algorithm. However, as the Internet becomes larger, this simple extension method becomes more and more increasing.
The reason is that:
- The overhead of the routing algorithm has become too large;
- A large number of completely different gateways participate in the same route algorithm, making management and error isolation almost impossible. Because it has been
Can't see the Internet as a complete communication system.
- Gateway software and algorithm, especially routing algorithm, deadboard and lack of flexibility, because any changes must pass too much
The department and too many people can do.
In the future, we hope that the Internet will evolve into a separate part or "autonomous system". Each is one or more
Compared with the same gateway. Agreement, especially (these gateways are used between them), the routing algorithm should be a private
People problems, and never need to be implemented inside the gateway unless special part or system.
In the simplest case, a self-government system consists only of a single gateway, and this gateway connects the local area to (eg) ARPA.
Online. We call this gateway for the "cigarette" gateway because his only purpose is to connect this network to the Internet.
He is part, neither intended to use the communication stream from the interior of the local network, no intended to use him to handle the network.
Communication flow of ground network. In the near future, we regard the Internet as a community of autonomous systems, one by ARP network and Stanet
The DARPA gateway is composed, others are some gateways to the LAN. The former is "core"
System - The latter is used as a transmission or "long-distance transport" system.
Finally, the Internet consists of a group of autonomous systems, each of which may be from arbitrary systems or to any system.
For the transmission medium. This common situation is still the topic of research. This thesis only describes how to use external gateway agreement
(EGP) Connect the "Cigarette" gateway to the core system.
2. Definition and Introduction In order to achieve the goal of this article, the cigarette gateway must be defined as:
- It is not a core gateway.
- It is at least with a core gateway (with one interface on the same network like some core gateways)
Share an interface.
- It has an interface that reaches one or more gateways without a core gateway.
- All other networks that can be reached through the core system of the cigarette butt, unless there is something else through the cigarette butt
The path of the core system.
The cigarette gateway is expected to complete the Internet Control Packet Protocol (ICP) and EGP protocols. Specifically, he must
It is necessary to respond to each request of ICMP. , Must send ICMP destination packets appropriately. He must also properly
Send ICMP redirection packets.
The autonomous system should be specified a 16-bit number (many of the same methods, such as the network and protocol
Number) and each EGP packet header contains one domain. Zero is not specified to any system; zero as
A autonomous system is usually used in future use.
We call two gateways for neighbors, if there is a network that reaches each gateway. If two
The gateway is part of the same autonomous system, we call them neighbors; if any two is on the same network
The two core gateways on the network are called internal neighbors. If the two gateways are not part of the same autonomous system, I
They call them to be external neighbors; if a core gateway and a cigarette cover share a network, we call it outside
Department gateway. In order to make another gateway to the communication medium, the gateway to each other must be able to know
A network must arrive through those networks. The external gateway protocol enables this information between two external neighbors.
Performance. Because it is a polling agreement, he also allows each gateway to control and receive the speed of network value information.
The rate allows each system to control its own overhead. He also makes each system have autonomous routing algorithms, these calculations
The law will not be interrupted because of the failure of other systems. The external gateway protocol has three parts (a) neighbor gain protocol (B)
Neighbor Dredibility Protocol and (C) Network Accessibility Judging. Note that all EGP definitions transmit only one stop. which is
They generated and sent to a neighbor gateway without meditation. Therefore, the survival time should
Set into a small number. If the gateway receives the EGP message in the message stream, the address is not pointing to them, the gateway will
Delete them.
Each EGP message contains a serial number. The gateway should maintain a serial number for each neighbor.
3. Neighbor
Before you get routing information from the external gateway, you must get it like a direct neighbor (directly adjacent
The difference between indirect neighbors will be explained below. In order to let the two gateways are called direct neighbors, according to the front
The definition of the meaning, and they must perform neighbors to get protocols, and simply tell him a two-time handshake standard.
A gateway to the neighbor request is launched, and a neighbor obtaining request is issued. This message should be heavy
Re-send (once every 30 seconds in the right speed), know that you receive a neighbor's response or neighbor
Reject. The request should contain a marker to copy the response and request to copy the answer.
The gateway that receives the neighbor obtaining request must determine whether it is a direct neighbor to become a requestor. if not,
He may be rejected with a neighbor to respond with a neighbor in its option. Otherwise he will send
Send a neighbor to receive a response message.
A request for the gateway should be considered that the neighbor has been completed after he receives the neighbor's response. Gateway issued
Neighbors have been completed, and after he issued an answer.
After a reasonable time, the non-match response and rejection were discarded. However, all these mismatched information
It is really useful for diagnostics.
A neighbor obtaining request request from the direct neighbor gateway shall be given a response as a response.
The neighbor request from the gateway g to gateway g 'or responds to the Neighborhood of g' of G '.
The minimum time period (in seconds) of the Hello packet and G are quickly removed from the NR packet (see below).
If a gateway does not want to become a neighbor that continues to be a specific external gateway, he sends a neighbor termination
Text. A gateway that receives a neighbor termination message is applied to a neighbor termination confirmation to respond. He should stop sending the sender
It takes place in any way. Because there are a large number of protocols run between direct neighbors (see below), if some
The gateway no longer needs to be other direct gateways. He uses a neighbor to terminate the packets and pointed out this fact. in
Before receiving its confirmation, the neighbor termination message should be repeatedly transferred until a certain number. After receiving the neighbor termination message,
The neighbor reachability protocol should be stopped processing.
The cigarette butt should have some tables, and there are some core gateways with his common network (only two to three)
the address of. The liability of the cigarette head should be to use these gateways to launch a neighbor. If the direct neighbor of the cigarette is all failed,
The cigarette butt has a minimum of a direct neighbor responsibility. It can do this, through the choice already become its room
One of the core gateways of neighbors (see below) and uses him to perform neighbor gain protocols. (At any time
Only one core gateway is always willing to be a direct neighbor of a given cigarette gate. )
4. Neighbor accessibility agreement
For a gateway, it is important to keep it such as neighboring accessibility. If one
The network is broken to determine a particular neighbor, and he should stop sending a communication stream to that gateway. In order to make judgments,
A neighbor canileability protocol is required. The EGP protocol provides two packet types - Hello and I Heard
You packet.
When you receive a Hello packet from the direct neighbor, you must immediately return to the direct neighbor to an i herd.
You packet. Never greater than a few seconds between I Heard You.
In order to determine the accessibility of an external neighbor, the core gateway will use the following algorithm:
A to reachable neighbors will be announced, if the core gateway sends N Hello last time, there is this
The answer received less than K I heard you. A non-reachable gateway should be announced, if the core gateway
The last time I sent a M-Hello and received at least J I heard you.
The cigarette gateway will also send them directly neighbor and will receive I heard you as an answer. Judgment
The algorithm of discrete can be similar to the algorithm described above. But sending Hello to the cigarette gate.
of. Hello and I Heard You packets have a condition domain, send gateways to indicate that he believes that the gateway is
Can it be reachable? This information is very useful for diagnosis. He also allows the cigarette gate gateway to give it the reachabilia
Dressing parasitic in its core neighbors: In fact, only the core gateway needs to send Hello packets. Cigarette tidry can be based on Hello
The inner state domain is to determine if it is up to. That is, the cigarette net (only I heard you) announced the core gateway (only
Send hello) as it can be reached, when hello from the core gateway pointed out that he has declared a cigarette butt.
The value of Hello's transmit frequency parameters k, n, j, and m cannot be specified here. The best results depend on neighbors and neighbors
The characteristics of the common network. This means that the appropriate parameters need designers and implementors from two neighbor gateways.
decided together. Do not care about the characteristics of neighbors and connected networks, and the isolated algorithm and parameter nine have no best to produce the best.
Reaches.
However, neighboring requests and response newsroom neighbors provide a minimum of Hello to each other to quickly answer Hello
Method of rate. When the gateway G sends a neighbor obtaining request to gateway G ', he declares that it does not want to be higher than X seconds
A speed reposted from g ''s Hello. G 'In its neighbor request answer, pointing out that it does not want to be above Y seconds.
The speed of the times replied from Hello. These two speeds do not have to be exactly the same. But each time you have to follow another
Interval. The gateway will send Hello at a lower than the required speed rather than a higher speed. The direct neighbor gateway should also be published as unreachable, if connected to its network used the remember agreement information, this
It can be inferred. However, for example, the gateway receives a destination issue of destinations from the Arpanet, pointing out one
Direct neighbors have died, the gateway should announce that neighbor is unreachable. Neighbors should not be announced as achievable, they will be exchanged
Before the number of Hello / I Heard You packs.
Direct neighbors that become unreachable will not stop becoming a direct neighbor. Neighbors can be published as arrival without
Get an agreement via a neighbor. However, if the neighbor keeps a long period of time, such as an hour, the gateway should
Stoping it as a neighbor, if you should stop sending Hello packets to him. Neighbor gain agreement should be repeated,
He became a neighbor again again.
Hello packets from non-direct neighbors should give simple discarding. However, all of this record can be mentioned
Very useful diagnostic information.
A ceiling gateway or it connects it to a gateway of a particular neighbor's gateway to stop, then it should send one
Neighbor Termination Packets give all direct neighbors that cannot reach its. Termination message is used in the information domain to indicate the shutdown cause. he
The message should be retransmitted many times and before he received a neighbor to terminate confirmation. Provide the neighbor to the neighbors
Report and make them ready to some extent, the most minimize the destruction of existing communications.
5. Network Can Deta (NR) Packet
Terminology: Assume that the gateway G has an interface to the network N. We said this G is relative to the network N (M and N
The separation of distant) is a suitable initial station that reaches the network M, when and only the following constraints:
The communication received on the network N interface to the network M and the gateway G will be forwarded to M by G, passing without including any
Another gateway with an interface to the network N. In short, the network M is combined when the network N is compared to the network n.
At the beginning. The network N can not be found to be a communication to the network M on the network N. About the best
Routing, communication to the network M on the network N should always be forwarded to a suitable primary station gateway there.
In order to make the external gateway G and G '(they make neighbors on the network N) to be used as a package switch to forward
To go to the network remote network communication, each need to understand the list of online listings as other networks. External gateway association
A message is defined, called network accessibility packets or NR packets to transmit this information.
Assume that G is a network located on the network N. The message that the network N sent to the last G must contain the following
information:
A full network list. The network in the table is all suitable initial stations for network N.
If g 'gets this information from the external neighbor G, then it knows the network to those who are not listed.
The communication of the network should not be forwarded to G. (However, all communications in the network cannot be simply concluded that all communications in the list will be forwarded.
Because g 'may have any other neighbor to arrive at N. For example, G and G "may be a neighbor of g ', but
The network N is equidistant. Each of that is a suitable initial station. )
For each network in the table, NR packets also specify "distance" from g to that network (according to autonomous)
Certain metrics of the definition of the designer of the gateway G in the system are used as an element). The core gateway should publish those who can leave
The distance from the core system can reach less than 128. The other is greater than or equal to 128. Net network
The distance between all the networks listed in its NR packet is published to less than 128.
The significance of the maximum value (255) means that the network is not strong. All other things worthy are networks.
If an NR message from the gateway G does not mention the network N, the NR packet from N is mentioned from N
Network N, then n may have been unreachable for G. If the continuous NR packets from g are mentioned
N, the end should be interpreted as being non-angle. This process is necessary to make sure that it is unreachable.
But not always announced. Network timeout and eliminating from the list of networks.
When a common situation, the core gateway G and the cigarette gate G 'are direct neighbors on the network N and know which networks of these neighbors are the first initial station. Although the cigarette net G 'may not know all other neighbors, it can
Convenient and efficiently get this information from g. Therefore, EGPNR packets also contain some allowed core gateways
G specifies the following information fields:
a) list of all neighbors (including internal neighbors and external neighbors) of G, these neighbors must
It is a reliable judgment to be judged. G can also include indirect neighbors in this list (see below).
b) For each of the neighbors, it can be used as a suitable initial station of which network in the network list (for network N
In the words).
c) Each
Therefore, NR packets provide a way, allowing a gateway to discover new neighbors, through a view
The neighbor has another neighbor on the same network. This information also makes the indirect neighbor described below
The implementation of the strategy is possible.
A more precise explanation of NR packets is as follows:
The data part of the message should be composed of data blocks, no blocks should be used as a title, this address
The address of the neighbor of the gateway or gateway that transmits this message should be sent. Each gateway address should be able to pass a network column
Table is understood as a suitable initial station for a network. All networks arriving at the same gateway should be organized here
In the list, add the distance itself and the network number. The whole list is before the table - the number of groups.
Data block list is:
a) The number of numbers (1 bytes) of the neighbor of the gateway G internal neighbors of the data block. Habitually
This quantity should contain G itself, it should appear in the first one.
b) The number of numbers of the number of the external neighbors of the gateway G is the data block included in this message.
c) The address of the network related to this message. If g and g 'are neighbors on the network N, then from g to
In the NR packet of G ', this is the address of the network N. The address of the four bytes has been assigned to this
1, 2, or 3 bytes at the end of the address should be zero.
Between each data block, the first block is G itself, then the block of all internal neighbors of g, and then the external neighbors
Hiving the block. Because all design of the gateway is on the same network, their address has been given, the network part of the gateway address
(1, 2, or 2 bytes) is omitted to save space.
In this network list, each network address is arbitrary one or three bytes. It depends on it; this is
A Class B or C address. There is no tail byte available. NR packets sent by a cigarette head should be the simplest
of. That is, it only has a data block, starting with its own address (it is common on the network and the neighboring core gateway), column
A network of suitable initial stations that can be reached. These are generally a network without other network paths.
The core gateway should send a complete NR message. Contains all information about other gateways on the same network,
There are core gateways (should be listed as internal gateways), there are other gateways (should be listed as external neighbors, may also include the cigarette head itself).
This information should turn the cigarette butt into an indirect neighbor of all of these other gateways (see below). Just, if appropriate
The cigarette butts should directly forward communication to these other gateways, but should not becomes their direct neighbors.
The cigarette butts should not be forwarded to any direct or indirect adjacent core gateway any of these gateways is not suitable for the first station.
Communication, like it is pointed out in an NR message. Of course, this cannot be applied to data on the source routing option.
News. Any such data retribution is always forwarded in the source route option domain, even if it is forwarded to one
Can be used as a gateway of the appropriate initial station.
6. NR packet polling technology
No gateway must send NR packets to any other gateway, except as an NR pollion from direct neighbors.
response. However, the gateway requires in response to a direct neighbor NR within a few seconds (subject to two restrictions)
polling. Even if the gateway believes that the neighbor has stopped.
The EGP NR polling packet is defined here. No gateway can be greater than 1 minute in a NR message
Ask other gateways. The gateway receives a polling greater than 1 minute may be simply given to ignore or send back an error message.
The gateway G will receive the spacing and g 'from the gateway G' to polls from gateway G.
The spacing minimum interval is specified as G and G 'to become direct neighbors. All neighbors get requests and neighbors get an answer
Allow the sender to specify its desired minimum polling interval (in seconds). If g is to reach G ', it is its most
The small polling interval is X, g 'should not poll the G. frequency at a frequency greater than X seconds. Polling must only be sent to a neighbor access protocol
Announced direct neighbors.
The NR polling message contains a serial number selected by the polling gateway. NRed by the polling gateway should be sent when responding to polling
This serial number is returned in the packet to in order to make the polling gateway to make the received NR packet and polling match.
In general, the polling should be retransmitted a certain number of times (in the retransmission room with a reasonable time interval) until an NR report
The text was received. If NR packets are received after the maximum number of retransmissions, the polling gateway should assume that the polled gateway is in any network.
Attention is not a suitable initial station. The best parameters of polling / retransmission algorithm should take depending on two gateways and connect them.
The characteristics of the network. The received sequence number is ignored by NR packets that are not matched recently. does not exist
Provisions for multiple prominent polling to the same neighbor.
7. Send NR packets
Typically, the NR report is only sent as a polling response. However, success in two external neighbors
Between polling, a gateway may send one and send only one active NR message to the neighbor, which gives him limited power
The fast advertisement may change the network accessibility of the network within the last polling. Too much NR message
May be ignored, or returned an error message.
NR packets should be issued in a few seconds after receiving the polling. Not as good as responding to a NR message may cause polling gateways
It is determined that the polled gateway is not a suitable first station for any network. As a polling sent by the NR newspaper
The number of sequence numbers in the text. The active NR message contains the identification number received by the previous polling, and has an active position
Set. (Note that this allows only only a single NR message / per polling period)
From non-neighbors, from neighbors who have not been announced, or have illegal IP source network domain, should be answered
EGP error messages with appropriate reasons. If g sends a NR polling packet to G '(with IP source network N)
And g 'is not a neighbor (g has an interface to the network N or, g' does not have an interface to the network N), the last network
The domain is considered illegal.
A gateway does not have to send more than one NR packet in the minimum interval, during the neighbor acquisition period. When there is an accident,
In order to copy polling (continuous polling has the same serial number), it must be done, this situation is in the polling in transmission
When it is lost. The gateway should send an NR message (the recent information contained in the answer) gives a copy polling.
8. Indirect neighbor
An external gateway turns into an indirect neighbor requires three steps: (a) Neighbor acquisition (B) running the accessibility protocol
(C) The neighbor is a periodic operation of NR packets. If the gateway G receives a NR message from g '. in
This G 'points out that there are some neighbors G1 ... GN. For a set of networks, each of the networks is a suitable initial station. That end
It is allowed to forward communication into these networks directly to the appropriate one of G1 ... GN without having to send G 'first. At this
In the case, G may be considered a indirect neighbor in G1 ... GN because it is considered to forward the neighbors of other gateways that are forwarded, but do not perform neighbor acquisition, neighbor reliability or use them to interchange NR messages. Neighbor and network accessibility information indirect
Through G ', "indirect neighbor" is specified. We say that G is an indirect neighbor of G1 ... GN.
If g is a G ''s indirect neighbor and g receives an NR report from G "(not involving g')
Wen, G should treat G 'as unreachable.
9. limitation
It must be clearly understood that the external gateway protocol is not established in its internal routing algorithm. In addition, it does not provide routine routing
The algorithm achieves all the information required. If the topology does not meet the achievement of the cigarette butt it gives, the external gateway protocol is
It is not possible to provide sufficient topology information to prevent circulation.
If any gateway issues an NR message with error messages, it is actually impossible to reach it.
The online application of the network, the communication of the network may never be delivered. Implementors must remember this.
A Appendix A - EGP Packet Format
The external gateway protocol runs above the Internet protocol, the protocol number is 8 (decimal).
A.1 neighbor acquisition message
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
- - - - - - - - - - - - - - - -
! EGP VERSION #! Type! Code! INFO!
- - - - - - - - - - - - - - - -
CHECKSUM! Autonomous system #!
- - - - - - - - - - - - - - - -
! Sequence #! Nr hello interval!
- - - - - - - - - - - - - - - -
Nr Poll Interval!
- - - - - - Description:
The neighbor acquisition message has internal and external gateways to become neighbors.
EGP VERSION #
2
Type
3
Code
Code = 0, neighbor acquisition request
Code = 1, neighbor acquisition answer
Code = 2, neighboring rejection (see information field)
Code = 3, neighbor death message (see information field)
Code = 4, neighbor death confirmation
CHECKSUM
The EGP checksum is the reverse code and 16-bit 1 of the 16-bit 1 of the EGP packets starting from the EGP version number.
In order to calculate the checksum, the check domain should be 0.
Autonomous system #
This sixteenth point pointed out that the autonomous system containing this packet source gateway.
Info
For reject messages, give rejection:
0 is not specified
1 get out of the table space
2 management prohibition
The reason for the termination of the neighbor is given to terminating the packet:
0 is not specified
1 stop
2 no longer need
Otherwise, this domain must be 0.
Sequence #
It is used to help match requests and answers.
NR Hello Interval
Minimum Hello polling interval (in seconds).
NR Poll Interval
Minimum NR polling interval (in seconds).
A.2 Neighbor Hello / I Heard You Packet
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
- - - - - - - - - - - - - - - -
! EGP VERSION #! Type! Code! Status!
- - - - - - - - - - - - - - - -
CHECKSUM! Autonomous system #!
- - - - - - - - - - - - - - - -
! Sequence #!
- - - - - - -
description:
External neighbors use the EGP neighbor Hello and I heard you packet to judge the connectivity of the neighbor. In a neighbor
When you receive a Hello message from a neighbor's EGP neighbor, it applies an EGP "I heard you" report
Text will respond.
EGP VERSION #
2
Type
5
Code
Code = 0, Hello
Code = 1, I heard you
CHECKSUM
The EGP checksum is the reverse code and 16-bit 1 of the 16-bit 1 of the EGP packets starting from the EGP version number.
In order to calculate the checksum, the check domain should be 0.
Autonomous system #
This sixteenth point pointed out that the autonomous system containing this packet source gateway.
Sequence #
It is used to help match requests and answers.
status
0 non-given conditions
1 For me, you look up
2 It seems that you are not up to the neighbor's accessibility protocol.
3 From network accessibility information, such as 1822 destination death packets from Arpanet networks)
You are not up to
4 Since my network interface problem seems to be unreachable
A3 NR polling message
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
- - - - - - - - - - - - - - - -
! EGP VERSION #! Type! Code! Unused!
- - - - - - - - - - - - - - - -
CHECKSUM! Autonomous system #!
- - - - - - - - - - - - - - - -
! Sequence #! Unused!
- - - - - - - - - - - - - - - -
! Ip Source Network!
description:
Description
The gateway wants to accept NR packets from the external gateway will send an NR POLL message. In NR packet
The gateways mentioned in the network have an interface on the network located in the IP source network. EGP VERSION #_
2
Types of
2
Code
0
Check and verify
The EGP checksum is the reverse code and 16-bit 1 of the 16-bit 1 of the EGP packets starting from the EGP version number.
In order to calculate the checksum, the checksum should be zero.
Independent system #_
This 16-digit number identifies the independent system
Contains the gateway that is the source of the message
Serial number
Help match requests and reply
IP source network
The gateways mentioned in NR packets have an interface on the network located in the IP source network. IP
The source network is marked as a network number of the one byte is the network number of the two bytes of zero to the Class A network number.
The code is followed by one byte zero for class B network and the three-byte network number is used for C networks.
A.4 Network Accessibility Packet
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
- - - - - - - - - - - - - - - -
! EGP VERSION #! Type! Code! U! Zeroes!
- - - - - - - - - - - - - - - -
CHECKSUM! Autonomous system #!
- - - - - - - - - - - - - - - -
! Sequence #! # Of int gwys! # Of extgys!
- - - - - - - - - - - - - - - -
! Ip Source Network!
- - - - - - - - - - - - - - - -
Gateway 1 IP Address (WITHOUT NETWORK #)!; 1, 2 or 3 Bytes - - - - - - - - - - -
! # Distances!
- - - - - - -
! Distance 1! # Nets!
- - - - - - - - - - - -
NET 1,1,1 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!; 1, 2 or 3 Bytes
- - - - - - - - - - - -
! NET 1,1,2 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!; 1, 2 or 3 Bytes
- - - - - - - - - - - -
...
- - - - - - -
! DISTANCE 2! # Nets!
- - - - - - - - - - - -
NET 1,2,1 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!; 1, 2 or 3 Bytes
- - - - - - - - - - - -
! NET 1,2,2 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!; 1, 2 or 3 Bytes
- - - - - - - - - - - -
...
- - - - - - - - - - - - - - - - ! Gateway N ip address (without network #)!
- - - - - - - - - - - - - - - -
! # Distances!
- - - - - - -
! Distance 1! # Nets!
- - - - - - - - - - - - - - - -
NET N, 1, 1 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!; 1, 2 or 3 Bytes
- - - - - - - - - - - -
NET N, 1, 2 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!; 1, 2 or 3 Bytes
- - - - - - - - - - - -
! DISTANCE 2! # Nets!
- - - - - - - - - - - - - - - -
NET N, 2, 1 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!; 1, 2 or 3 Bytes
- - - - - - - - - - - -
NET N, 2, 2 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!; 1, 2 or 3 BYTES - - - - - - - - - - - - - -
...
Description
Network Cavity Message (NR) is used to find the network that may arrive through the external gateway. Send NR report
Surveying a NR Poll message.
EGP VERSION #_
2
Types of
1
Code
0
Check and verify
The EGP checksum is the reverse code and 16-bit 1 of the 16-bit 1 of the EGP packets starting from the EGP version number. for
Calculate the checksum, the checksum should be zero.
Independent system #_
This 16-digit number of the independent system contains that is the gateway of the message.
U (unshold)
This bit is set if NR packets are not sent.
Serial number
The last serial number of the NR POLL packet sent by the neighbor is the NR POLL message that is being transmitted. This one
The number used to help match polling and reply.
IP source network
The gateways mentioned in NR packets have an interface on the network located in the IP source network.
Internal gateway #_
The internal gateway mentioned in this message.
External gateway #_
External gateways mentioned in this message.
Gateway IP address
1, 2 or 3 bytes of the gateway IP address (no network #_).
distance
Number of gateways.
distance
distance
network
Number of nets in this distance.
website address
1, 2 or 3 bytes of the network address of the network that can reach the front gateway.
A.5 EGP error message
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
- - - - - - - - - - - - - - - -
! EGP VERSION #! Type! Code! Unused!
- - - - - - - - - - - - - - - -
CHECKSUM! Autonomous system #!
- - - - - - - - - - - - - - - -
! Sequence #! Reason!
- - - - - - - - - - - - - - - !!
Error Message Header!
! (First Three 32-Bit Words of EGP HEADER)!
!!
- - - - - - - - - - - - - - - -
Description
EGP error messages have an incorrect value as an illegal verification or in one domain.
Response delivery of EGP packets.
EGP VERSION #_
2
Types of
8
Code
0
Check and verify
The EGP checksum is the reverse code and 16-bit 1 of the 16-bit 1 of the EGP packets starting from the EGP version number.
In order to calculate the checksum, the checksum should be zero.
Independent system #_
This 16-digit number of the independent system contains that is the gateway of the message.
Serial number
Send an error message via the gateway.
reason
EGP packets have an error reason. The following reasons have been defined:
0 - not detailed
1 - Illegal EGP checksum
2 - Illegal IP source address in Nr Poll or response
3 - Unselected EGP type or code
4 - Received Poll from non-neighbor
5 - received too many unsolicited NR messages
6 - received too many poll
7 - Incorrect statistics in NR packets
8 - No response from NR Poll
0 - not detailed
RFC888 - "Stub" Exterior Gateway Protocol "Cotta" external gateway protocol
1
RFC Document Chinese Translation Program
