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RFC 827
.................................. External Gateway Agreement (EGP)
.................................. Eric C. Rosen
Bolt Beeranek and newman Inc.
October 1982
It is used to establish a standard for the gateway and can be handled with a gateway that is suspicious. This document is a draft of the standard. Your opinion we warmly.
RFC 827 Bolt Beeranek and newman Inc.
Eric C. Rosen
table of Contents
1 introduction ........................................ 1
2 neighzor detection .................................. 8
3 neighboring machine accessibility agreement ..................... 11
4 network accessibility (NR) packet .................... 15
5 NR packet poll ............................ 22
6 Send NR packets .................................. 25
7 indirect neighbors ............................... 27
8 How to become a branch network ........................... 28
9 limitations ........................................ 32
1 Introduction
DARPA satellite network CateNet should be a constantly developing system, there are more and more hosts and more and more networks to participate. Of course, this will need more and more gateways. In the past, an extension was carried out in a relatively non-tissue manner. New gateway - often contains the completely different software with existing gateways - will continue to increase, and will immediately participate in public routing algorithms through the GGP protocol. However, with the growing development of the international Internet development, this simple expansion method has become increasingly increasing. There are many reasons:
- The turnover of the path selection algorithm has become too large;
- Since the various very different gateways of the single public path selection algorithm are increasing, there cannot be repaired and fault isolation, because the Internet is never treated as an integrated communication system.
- Gateway software and algorithms, especially path selection algorithms, becoming too strict and unflexible, because any proposed changes must be done with too many different locations with too many different people.
In the future, the Internet should develop into a set of independent å or "autonomous systems", each containing a set of relatively assigned gateways (there are one or more). Agreement, especially the protocols used in them themselves, will be dedicated, and do not need to be implemented in a specific domain or gateway outside.
In the simplest case, a self-governing system may only contain a single (e.g., connecting a local area network to the gateway on the Arpanet. Most of the gateways like this are called "branch gateways" because its unique use is to connect the local area network to the other parts of the Internet, rather than intend to process any communication from or to that particular local area network. In the near future, we will consist of Internet networks as a community of autonomous systems, which consist of a Darpa gateway located on the Arpanet and SatNet, and the rest is the branch gateway to the local area network. In the front system, we should be called the "core" system, which will be subsequent systems as a transportation or "long-distance" transportation system. However, the Internet may ultimately consist of many equality autonomous systems, and any of them can be used as (with certain constraints, will be discussed later from any system and to communicate to any system. medium. When a more complex combination occurs, any autonomous system is considered a "core" system apparently not suitable. However, for the specific start, and because the initial implementation of the external gateway protocol should be centrally connected to the Darpa gateway located on the ArpaNet and SatNet, we will use the term "core" gateway in our instance and discussion. .
The purpose of the external gateway protocol (EGP) is that when the end user is allowed to treat the complex of all autonomous systems as a single international internet network, use a fixed, unified address space, so that one or more autonomous systems can be used as a self Use in other autonomous systems and the propagation medium to communicate into other autonomous systems. Data reported through the routing of the Internet and the number of autonomous systems across the autonomous system (of course, unless the end user uses the IP "source routing" option).
In the description of the external gateway protocol, we deliberately leave a lot of activities in the designer and realizes of special self-government systems, especially in the timer size. The reason why we do this is because we have different gateways to achieve different demand and goals, so there is no single clear implementation specification for all situations. However, this does not mean that any implementation that meets this specification is working properly, or we have left the event, it is irrelevant to performance.
In fact (for example), there is no specified timeout here, but it does not mean that an arbitrary value can work very well.
The autonomous system will be specified a 16-bit identification number (now many times, using the same method to distribute encoding), and each EGP header is stored for this number. Zero will not assign to any autonomous system; more exactly, there is a zero in this domain that will indicate that there is no number.
We must introduce a gateway to another gateway's neighboring machine (NEIGHBOR). In the simplest and most common cases, if there is a network that has an interface to the interface to this network, we call these two gateways as "neighters". However, in order to allow the following two cases, we need a broader "neighbor" concept:
a) Two gateways can be considered to be neighboring machines, although they are not directly connected by a (in general terminology) network, but through a single link, HDLC line, or some analog "direct connection". b) The two gateways can be considered a neighbor, although they are connected by a transparent "Internet" through a transparent.
That is, we hope that the two gateways are neighboring machines, even if they are connected through an Internet, as long as the gateway does not use the INTERNET's internal structural knowledge in their package transition algorithm.
In order to deal with all these cases, we say that the two gateways are neighboring machines, if they are connected to them through some internal structures. (Neighboring machine concept is more comprehensive discussion) See Ien 184.)
If the two neighbors belong to the same autonomous system, we call them internal neighbors; if the two neighbors do not belong to the same autonomous system, we call them external neighbors. For a system to use another as a propagation medium, a gateway that is mutually external neighbors must be able to find out which networks can be reached via other networks. The external gateway protocol enables this information between external neighbors. Because it is a polling protocol, it can also control each gateway to control the speed of sending and receiving network accessibility information, allowing each system to control its own overhead. It also enables each system to have an independent routing algorithm that does not occur due to faults of other systems. It must clearly know that all self-government systems will be completed between the gateways within the system that have their own routing algorithms. (Single autonomous system consisting of a single branch gateway usually does not require a routing algorithm.) The external gateway protocol is not a routing algorithm. It enables external neighboring machines to exchange all routing algorithms, but the gateway does not specify how the gateway handles this information. The "routing update" of the internal routing algorithm of certain autonomous systems may (or may not) implate in the format of the external gateway protocol. The gateway in the Darpa "core" system will start using the GGP protocol (old gateway to gateway protocol) as their routing algorithm, but these changes. The gateway in other autonomous systems may use their own internal gateway protocol (IGPs), may or may not be similar to any other autonomous system IGP. Of course, GGP can be used, but it is not allowed to exchange GGP packets in the gateway in other autonomous systems.
It must also be clearly known that the external gateway protocol is not intended to provide information that can be used as an input as a normal range or a layered routing algorithm. It is designed for a set of autonomous systems connected to a tree, without loop. It cannot pass full information to prevent routing, if the loop is in the topology. The external gateway protocol has three parts: (a) Neighboring machine detection protocol, (b) Neighborhood accessibility protocol, and (c) network Sexual judgment. Note that all messages defined by the EGP are only used to propagate a single "journey". That is, they launched a gateway and go to a neighbor gateway, without the gateway between them.
Therefore, the survival time (TTL) domain should be set into a small value. The gateway that encounters EGP packets in the message stream may drop them.
2-neighboring machine detection
Before getting routing information from an external gateway, the gateway must be acquired as a direct adjacent. (Directly and indirect neighbors are given in the chapter behind.) In order to make two gateways to direct adjacent, they must be a neighbor, and they must run just a standard. Three handshake neighbor control protocols.
A gateway hopes to activate the neighbor detection with another gateway, then send it a neighbor detection request. This message should be repeated (at an appropriate speed, approximately every 30 seconds) until you receive a neighbor probe response. This request always contains an identification number to copy to a response, so request and response can be paired.
The gateway received from a "Neighbor Probe" must determine if it wishes to become a direct neighbor that requests the initiator. If not, it can respond to a neighboring machine to reject packets with a neighboring machine, freely stipulating reasons. Otherwise, it should send a "neighbor detection response" message. It must also send a "neighbor detection request" message unless it has already done this.
The two gateways turns into direct neighboring machines, and when each neighbor detection message has been sent to another, and the corresponding "neighbor detection response" from another has been received.
The non-match response or refused to be discarded after a reasonable time. However, information about all these mismatched messages may be useful for diagnostics. "Neighbor Detection Packet" from a direct neighboring gateway should be used in response to a "response" and a "neighbor detection message".
If a "neighbor detection response" is received from an intended neighbor, after a period of time, there is no "neighbor detection message" of the expected neighbor, the neighbor detection agreement should be considered yet. . A "neighbor termination" message (see below) is sent immediately. If a gateway still wants to get another as a neighbor, the protocol must start from the beginning.
If a gateway wants to terminate the neighbor of an external gateway, it sends a "neighbor termination" message.
The gateway that received the "Neighbor Termination" message should always be in response to confirm with a "neighboring machine termination". It should stop treating the senders of the message as an armed machine. Because there are many protocols running in direct neighboring machines (see below), if a gateway does not need to be other direct neighbors, it pointed out this fact with a "neighbor" message "polite". The "neighbor termination" message should be repeated (until some number) until it receives it. Once a "neighbor termination" message has been received, the neighboring accessibility protocol (below) should stop running.
Note that we have not specified a gateway to begin to decide how to turn into another neighbor.
Because this is just a normal problem, it does not belong to the external gateway protocol.
3-neighboring machine accessibility protocol
Keeping real-time information on the reachability of its neighboring machines for the gateway. If a gateway is inferred that a neighbor is not reached, it will stop forwarding communication to that gateway. In order to make judgments, the neighboring accessibility protocol is required. The external gateway protocol provides two message types - a "Hello" message and a "I heard you" packet.
When you receive a "Hello" message from a direct neighbor,
It must be "immediately" to return to the neighboring machine to another "I heard you". Received a "Hello" and returning a "I heard you" is not greater than a few seconds.
At that time, the reachability judgment algorithm left the designer of a specific gateway to complete. Our ideal algorithms are as follows:
A can be reached should be announced as unreachable. If we recently sent N "Hello" during this, only the response received less than k "I heard you". A undeavored neighboring machine should be announced, if we recently send M "Hello", at least J "I heard you" response during this period.
However, this is not specified in the transmission frequency of "Hello" and the value of parameters K, N, J, and M. As for how to get the best results, this depends on the characteristics of the neighboring machine and the characteristics of the shared network of adjacent machines. This means that the appropriate parameters should be determined by the designers and realizes of the two neighboring gateways. There is no wish to produce the most appropriate accessibility judgment without considering the characteristics of the neighboring machine and the connected network.
"Hello" and "I Heard You" message have a state domain, "Send" gateway is used to indicate that he thinks "accepting" gateway or is not accessible? This information can be used for diagnostics. On the other hand, it also allows a gateway to attach the accessibility judgment: In fact, only one gateway needs to send "Hello" packets, and the other can declare it in the state domain in "Hello" to boot or shut down. That is to say, when "Hello" from the active gateway, "Hello" indicates that the passive gateway is achievable, the passive "gateway (only" I heard you "declare" active "gateway (only Sending "Hello") can be achieved.
Of course, only which neighboring machine is active in advance to work. (The prior agreement here is not part of the external gateway protocol.)
The direct neighboring gateway should also be declared as unreachable, if this is the case where the underlying protocol information can be inferred from the underlying network of the network. Therefore, for example, a gateway receives a 1822 destination whose direct neighboring flameout is turned off from Arpanet, which should not be reached. Until the required number of Hello / I Hello / I HEARD - YOU package has been exchanged, the neighboring machine is still declared as achievable.
A direct neighboring machine that has become unreachable is no longer a direct neighbor. No need to experience the neighbor detection protocol again, the neighboring machine can be declared once again. However, if the neighbor is not allowed for a long period of time, for example, an hour, the gateway should stop depending on it is a neighbor, that is, should stop sending "Hello" packets to it. Neighboring machine detection protocols will need to be retransmitted before it becomes a direct neighboring machine.
The "Hello" and "I Heard You" packets from the gateway G go to Gateway G 'also carries the identification number of the NR polling packets recently received from g'. "Hello" and "I heard you" packets from gateway G to Gateway G 'may carry G. The minimum time interval of g' to NR Messages in minutes.
"Hello" messages from non-direct neighbors should be simply ignored. However, documentation can be used to provide useful judgment information. A gateway stops or connects it to a neighbor interface. It does not work properly. You should send a gateway shutdown message to all direct neighbors that cannot reach its. It should repeat the message (until a certain number) until it receives a gateway shutdown to confirm that it provides a pre-alarm of the neighboring machine, allowing them to prepare a way to make the existing communications to achieve the minimum .
Terminology: The gateway G has an interface to the network N.
We said: G relative to network N (M and N is different networks) is the reasonable first battle to network M, when and only when the following cases occur:
The amount of traffic to the network M and the network N interface to reach the gateway G is always forwarded by the path to M via a path that is not included with the gateway connected to the network N.
Briefly, for the network n, G is a suitable initial station to the network M, in which case there is no better gateway on the network N to route traffic to the network M. In order to perform the best route, the amount of traffic to the network M in the network N should always be forwarded to the gateway of the appropriate initial station.
In order to make the external neighbors G and G '(through the network N are neighboring machines) can be used as a package switch to the remote network with each other, each must know another network list in order to be the appropriate initial station to it. . The external gateway protocol defines a message, called Network Reachability Message (or NR Packet) for delivery of this information.
Let G be a gateway on the network N. G Send NR packets sent by the network N must contain the following information: Lists G are all networks of the starting initial station for network N.
If g 'can obtain this information from the external neighbor G, it knows that the traffic to the networks that are not in the list should not be forwarded to G. (However, all traffic on the network located in this list should not be easily forwarded, because g 'may have other neighbors, and these neighters are also suitable for the first quarter of the network N. For example, G And g "may be a g ''s neighbor, but for NetWork m may be" equal distance ". So each of them can be a suitable first station.)
For each network in the list, NR packets also contain one byte indicating "distance" from g to that network (according to certain metric, these metric leaves designer to design the autonomous system containing the gateway G).
This information may (or may not) top the diagnosis or internal routing algorithm.
The distance maximum (255.) means that the network is unreachable. All other things mean that the network can be achieved.
If a NR message from a gateway G is not described in the NR packet from the aforemention, it is mentioned that a network N should be assumed that he is still achievable for g him. However, if N is mentioned in two consecutive NR messages from G, it means that n is not arrived for G.
To ensure that those that are not arrogant but never explicitly declared as unreachable, this method is necessary.
G and g 'are external neighbors on the network N, G knows a large number of gateways on the network N, and know that these neighbors are the appropriate initial stations of those networks. Because g 'may not know all of these neighbors, it is more convenient and more efficient from G. Therefore, the external gateway protocol NR message also includes allowing to describe the following information:
a) A list containing all neighbors that G have been reliably determined (both internal neighbors also include an external abutment). This gateway is only included in this list only when the G actively uses them to run the neighbor accessibility protocol.
b) Each neighbor in the middle of the neighboring machine has a corresponding network list. For network N, this neighbor is the appropriate initial station of these networks. c) "NETWORK" pairs such as each image, indicating "distance" from that neighbor. Therefore, NR packets provide a method that allows a gateway to discover new neighbors to discover new neighbors on whether or not other neighbors on the same network is available.
This information makes it possible to make the indirect neighbor strategy defined below.
The following is a more accurate description of NR messages.
The data part in the packet contains a large number of data blocks. Each block is always headed by a gateway address, which may be an address of the address of the gateway or an address in the neighbors of the gateway. Each gateway address may have a network list and from that gateway to each network, for those network the gateway is a suitable initial station.
Before putting the list of data blocks:
The address of the network related to this message.
If g and g 'is a neighbor on the network N, then in the NR packet from g' to G ', it is a network N address.
For convenience, four bytes have been given to this address - one, two or three bytes at the end should be zero.
b) The total number of internal neighbors is the number of data blocks included in this message. According to the practice, the total number will contain the data block of the G itself, which should be the first appearance. c) The total number of external neighbors of g is the number of data blocks included in this message.
Then the data block itself, the first is G itself, then the block of all the internal neighbors of G, and then the external neighboring block. Because all the gateway addresses mentioned on the same network have been given, the network address portion of these gateway addresses (one, two or three bytes) is omitted in order to save space.
Each data block contains a byte to calculate the number of networks that can be used as a network of suitable initial stations. In this network table, each network address is one, two, or three bytes, depending on it is a Class A, Class B address, or Class C address. Thereafter, the byte followed is not used.
Sometimes the NR packet must be segmented. NR contains a byte to indicate the number of fragments (the segment is encoded from zero), and one byte is encoded with the last piece (the number of pieces). If there is no segmentation, these bytes must be all 0. Each clip must be a complete independent NR message. That is, each fragment starts calculation from the internal gateway and the external gateway, which will be the integer multiple of the block. The number of data blocks in each segment must correspond to the number of calculations from that debris. However, only the first fragment uses a data block describing the send gateway as a start.
This scheme allows each fragment to process independently, and does not require a complex assembly mechanism. It also handles all pieces that have not been received yet. If you have not received all pieces after a period of time or retransmission polling, you should handle existing segments If they can form a complete NR message. (This means that only the network mentioned in the error segment will keep the "distance" value in the NR packet from that gateway. However, if this network is not subject to the next NR message from that gateway A new value, the network will be declared as unreachable.)
5 NR packet polls NR packet polling
No gateway will require send NR packets to any other network management unless a NR poll response from a direct neighboring machine. However, a gateway is required to respond to NR polling from a direct neighbor (according to the following two paragraphs) within a few seconds, even if the gateway is confident that the neighbor is downtime.
The EGP NR polling message is defined for this purpose for an NR packet gateway without polling at a frequency above a minute. If the gateway receives multiple polls within a minute, it simply discards additional polls, and may return an error message. The gateway G is sent to the "Hello" and I Heard You packets of the gateway G 'indicates the minimum time interval between G' to accept the polling interval. That is, G 'does not guarantee the response from the G less than that interval.
Polling must be sent to the neighbor accessibility protocol declaration as a reachable direct neighbor. ?
An NR polling message contains an identification number, which is selected by the polling gateway.
The polled gateway will return this serial number in the NR packet, sending his polling as a response, allowing the polling gateway to match the received NR packet. Choose a unique identification number to allow the detected NR packets that may be propagated in the network, which is the responsibility of the "polling" gateway. Because the polling is relatively rare, there will be no more problems. However, in order to help choose a log number!癏 Ello "and I Heard You packets are carried from the identification number of the previous NR poll. Usually, the polling should be repeatedly transmitted a certain number of times (transfer with a certain time interval) until a NR message is received After the maximum number of retransmission, there is still no NR packets, and the polling gateway should assume that the polling gateway is not a suitable initial station for any network. The best parameters of polling / retransmission algorithm depends on two Neighboring machine features and the characteristics of connecting their networks.
This segment should be consisting of the entire NR packet as long as a segment of a NR message is received after the maximum retransmission.
NR packets receiving the identification number and the recently sent polling should be ignored. There is no specified multiple protruding polling to the same neighbor.
6 Send NR packets
Typically, NR messages are only transmitted as a polling. However, between two consecutive polles from an external neighboring machine, the gateway may send a unique NR message to the neighboring machine. This allows him to have limited capacity to quickly announce network accessibility, which may already exist within the last polling. Excessive unsolicited NR packets are discarded or returned to an error message.
NR messages should be sent in a few seconds after the polling. If it is not in time to respond to an NR polling, the polling network is turned off to determine the appropriate initial station for any network. ? *}
NR packets transmitted as a polling response to the identification number with the polling in their label number domain. The identification number of the last received polling is not requested by requesting NR packets, as well as the "unrupt" bit setting. (Note that it allows only one non-request NR packet for each polling period.)
In order to easily send the NR packets, NR polling packets have one byte indicating that the polling interval is in minutes.
Polling from non-adjacent and neighbors from no declarations or a polling with an illegal IP source network should be responded by EGP error messages with an appropriate "reason" domain. If the G transmits an NR polling G 'having an IP source network N, G' is not a neighbor of g ', (or the interface of g' does not reach the network N), so the source network domain is It is considered to be illegal.
The copied polling (continuous polling has the same identification number) should be responded to the replica of the same message. If the message is segmented, the same segmentation number should be sent each time. Note that there is no provision for protruding polling from a single neighbor. Note If the same segment does not send a response replica polling, the wrong re-assembly will happen. If it is not split, then use a different (estimated possible closer) NR message response to a copy polling should not cause damage.
7 indoor neighbors
"Direct neighbor" becomes an external gateway requires three steps: (a) Neighboring machine detection, (b) runs a neighboring machine accessibility protocol, and (c) the NR packet periodically polled the designer. However, it is assumed that the gateway G receives an NR packet from g ', where g' points out that there are other adjacent machines G1, ..., GN, for a group of g 'is not its suitable initial station, each is a suitable First station. Then G should allow forwarding the traffic of those networks directly to G1, ..., GN, without having to send to G 'first. In this case, G may be considered an indirect neighbor for a G1, ..., GN, because it is to forward traffic, but no abutment machine detection, neighbor accessibility, or exchange NR messages with them An neighbor for other gateways. The adjacent machine and network accessibility information can be indirectly obtained by g ', and thus is called an "indirect abutment machine." We said that G is a indoor neighbor for G1, ..., GN via G '.
If g is an indirect neighbor for g 'via g, and g receives an NR message from g "not mentioning G', G should see G 'as a non-arrival.
8 How to become the most common external gateway protocol for a branch network may be able to communicate with a branch gateway with a national defense senior research project management bureau, so that data streams between networks can only pass through the branch line or Only by core network system - can be accessible to each other. As mentioned above, a branch gateway can be seen as a one-level international internet system, which does not have an internal neighbor. He is often used in the LAN or the network to reach a long-distance transportation network with a core gateway (such as anapa and satellite network). In this case, this bridge network does not require any core gateway to forward him to come to something that can be reached by this bridge network. Typically, the network network does not provide any services to the International Internet Transportation System, and does not need to be transferred from or to whether the traffic to the network can be transferred.
The branch should have a network table containing a small number of core gateway addresses (no more than two or three), which have a public network. The responsibility of the branch line gateway uses these gateways to start the abutment of the neighbor. When a branch gateway and a core gateway become direct neighbors, the core gateway will start sending Hello packets.
When the branch gateway declares that the core gateway that has become a direct neighboring machine is arrived, he should poll these gateways for NR packets per minute (or in accordance with Hello packets from core gateways) . The core gateway should be polled by NR packets.
The NR packet sent by the branch should be the simplest allowable. > That is, it should only have a single data block, starting with its own (on the network of the network adjacent to the core gateway), only listing it is a suitable initial network. Usually these are probably a network that can reach other ways.
The core gateway sends a complete NR Messages that contains the introduction of all other gateways on the public network, which should be included in internal neighbors) and other gateways (should be included in the external neighbors, and may include the branch itself). This information may enable the branch line into one indoor neighbor for all of these other gateways.
That is, the branch should forward the traffic directly to these other gateways, but will not turn to them into direct neighbors.
The core gateway always reports a distance of less than 128. If the network can be reached without the core system (ie, the gateway does not cross any non-core gateway), it is greater than or equal to 128.
The fund will never give any (directly or indirectly adjacent core gateway to the gateway that is not a suitable initial station, which is pointed out in an NR message. Of course, do not apply to the use of the source routing option. Data reports; Anyone like this should always be forwarded like a source route, even if it is necessary to forward a gateway that is not a suitable initial station.
If the direct neighboring machine of the branch is completely unacified, its responsibilities are at least a new direct neighbor. It is done by selecting a core gateway that has become an indirect neighbor and then uses it to perform a neighbor detection protocol. (Not more than a core gateway will agree to becomes a direct neighbor machine for the branch gateway given at any time.)
If the branch gateway does not respond to the "Hello" message from the core gateway in time, it may be declared as unreachable. If the branch gateway does not respond to NR polling packets from the core gateway in time, its network may be declared as unreachable. In these cases, the core gateway may drop traffic to those networks, and return the source host to ICMP "destination networks".
The branch gateway should completely run the ICMP protocol, as well as the external gateway protocol. In particular, it must respond to ICMP ECHO requests, and must send ICMP destination out of the message as appropriate. It also requires sending ICMP redirection messages as appropriate.
9 limitations
It is not in the form of a network path selection algorithm. In addition, it cannot provide all information necessary to implement the general routing algorithm. If the topology of the autonomous system is not a tree structure (ie, if it has a loop), the external gateway protocol does not provide enough topologies to prevent loop.
If any gateway sends a fake information NR packet, claiming to be a suitable first starter station, but in fact, it can't be reached, and the communication of the Pu Net has never be delivered. Implementers Must Bear this in mind.
Neighboring machine detection 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 #!
- - - - - - - - - - - - - - - -
Identification #!
- - - - - - -
Description
The internal and external gateways becomes "neighbor detection packets" into an adjacent machine. EGP version 1
Types of
3
Code
Code = 0 "Neighboring Detection Request"
Code = 1 "Neighboring Detection Response"
Code = 2 Neighbor Value Detection Rejection (see Information Field)
Code = 3 "Neighbor Termination" packet (see information field)
Code = 4 "Neighbor Termination" confirmation
Check and verify
EGP checksum is 16-bit binary inverse code value in EGP packets starting from the EGP version number field. In order to calculate the checksum, the checksum should be zero.
Independent system #_
This 16-digit identifies the independent system that contains a gateway for the source of the packet.
Info
For reject messages, give reasons for reject:
0 Underated
1 is not in the potential neighboring machine
2 prohibited due to management settings
3 For stop packets, give the reason why it is no longer a neighboring machine:
0 is not specified
1 shutdown
2 No longer need to be adjacent machine communication
Otherwise, this domain must be zero.
Logo number
Help match the identification number of the request and the response.
Neighboring machine hello / i heard you
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 #! Min poll intvl! Zero!
- - - - - - - - - - - - - - - -
Last Poll ID #!
- - - - - - -
Description
The external neighboring machine uses the EGP neighbor "Hello" and I heard you packet to determine adjacent connectivity. When a gateway receives the EGP neighbor "Hello" message from the neighboring machine, it should respond to a EGP I heard you packet. External gateway protocol version
1
Types of
5
Code
Code = 0 for "Hello"
Code = 1 for i hers you
Check and verify
EGP checksum is 16-bit binary inverse code value in EGP packets starting from the EGP version number field. In order to calculate the checksum, the checksum should be zero.
Autonomous system #
This 16-digit identifies the independent system that contains a gateway for the source of the packet.
Sequence number
Help match the serial number of the request and response.
status
0 No status information
1 looks like I can visit you
2 2 According to the neighboring machine, I can't access you.
3 3 According to the network accessibility information I have visited you (eg, 1822 "destination from Apa," packets)
4 4 Due to my network interface problem, I don't have you.
Previous polling identification number
From this, it is preparing to send it to the NR polling packet of NR polling packets recently received from the neighboring machine there.
Minimum polling interval
One minute, during this period, the gateway should not poll the NR packets than once.
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 #!
- - - - - - - - - - - - - - - -
! IP Source Network! Interval!
- - - - - - - - - - - - - - - -
Identification #!
- - - - - - -
Description
The gateway wants to accept NR packets from the external gateway will send an NR POLL message. The gateways mentioned in the NR packet have an interface on the network located in the IP source network. External gateway protocol version #
1
Types of
2
Code
0
Check and verify
EGP checksum is 16-bit binary inverse code value in EGP packets starting from the EGP version number field. In order to calculate the checksum, the checksum should be zero. Autonomous system #
This 16-digit identifies the independent system that contains a gateway for the source of the packet.
Logo number
Help match the identification number of the request and the response.
IP source network
The gateways mentioned in the NR packet have an interface on the network located in the IP source network. The IP source network is marked as a network number of one byte is the two bytes of zero to the A-network number of the network numbers. The network number of the two bytes is one byte zero for class B network and the three-byte network number is used. Class C network.
time interval
The polling interval in minutes.
Network accessibility 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! U! Zeroes!
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CHECKSUM! Autonomous system #!
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! Fragment #! # Of last frg.! Identification #!
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! Ip Source Network!
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! # of int gwys! # of ext gwys!
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! # of nets!;; # of Nets for
- - - - - - - - - - - GATEWAY 1
! Gateway 1 IP Address (WITHOUT NETWORK #)!; 1, 2 or 3 Bytes
- - - - - - - - - - ! Net 1, 1 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!; 1, 2 or 3 bytes
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! distance!
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! NET 1,2 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!; 1, 2 or 3 bytes
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! distance!
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.
.
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! Net 1, M !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!; M Nets Reachable
- - - - - - - - - - Download Adaises; Via Gateway 1
.
.
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! # of nets!; Number of Nets for Gateway N
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Gateway N IP Address (WITHOUT NETWORK #)!
- - - - - - - - - - - - - - - ! Net N, 1 !!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!; 1, 2 or 3 bytes
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! distance!
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NET N, 2 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!; 1, 2 or 3 bytes
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! Distance!
- - - - - - - - .
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Net N, M !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!; M Nets Reachable
- - - - - - - - - - Download Adaises; Via Gateway N
! distance!
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Description
Network Cavity Message (NR) is used to find the network that may arrive through the external gateway. Send NR packets in response to an NR Poll message. ^ YXok90
External gateway protocol version #
1
Types of
1
Code
0
Check and verify
EGP checksum is 16-bit binary inverse code value in EGP packets starting from the EGP version number field. In order to calculate the checksum, the checksum should be zero.
Autonomous system #
This 16-digit identifies the independent system that contains a gateway for the source of the packet.
U (without request)
This bit is set if NR packets are not sent.
Logo number
The last identification number of the NR POLL packet sent by the neighbor to this NR packet that is being transmitted. This number is used to help match polling and reply. Segment number
The segmentation in this NR message. If there is no segmentation, zero.
The last segmentation number
The number of previous segments in this NR message. If there is no segmentation, zero. IP source network
The gateways mentioned in the NR packet 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.
The internet#_
It is the number of gateway IP addresses of the appropriate initial station to follow the number of networks.
Gateway IP address
1, 2 or 3 bytes of the gateway IP address (no network #_).
website address
1, 2 or 3 bytes of the network address of the network that can reach the front gateway. 1 byte distance in the site #_.
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
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! EGP VERSION #! Type! Code! Unused!
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CHECKSUM! Autonomous system #!
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Error Type! Error Code! ID. # Of erroneous msg.!
- - - - - - - - - - - - - - - -
! Sequence #!
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Description
EGP error messages are delivered as responses to EGP packets with illegal values or EGP packets with incorrect values in its domain.
External gateway protocol version #
1
Types of
8
Code
0
Check and verify
EGP checksum is 16-bit binary inverse code value in EGP packets starting from the EGP version number field. In order to calculate the checksum, the checksum should be zero. Autonomous system #
This 16-digit identifies the independent system that contains a gateway for the source of the packet.
Sequence number
Send an error message via the gateway.
Error type
Errors type of EGP packet
error code
Error EGP message code
Identification number of incorrect message
The serial number of the wrong EGP message
the reason
EGP packet error reasons The following reasons have been defined:
0 - not specified
1 1 - Illegal EGP checksum
2 2 illegal IP source address in NR polling or response
3 3 - 3 - Undefined EGP type or code
4 4 - Received polls from non-neighboring
5 5 - Received too many unsolicited NR messages
6 6 - received too many polls
77- Error calculation received NR packet
8 8 - Nothing received NR polls
9 9 - Not all received NR packet segmentation
