📄 rfc888.txt
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RFC 888 JANUARY 1984 The EGP checksum is the 16-bit one's complement of the one's complement sum of the EGP message starting with the EGP version number field. For computing the checksum, the checksum field should be zero. Autonomous System # This 16-bit number identifies the autonomous system containing the gateway which is the source of this message. Info For Refusal message, gives reason for refusal: 0 Unspecified 1 Out of table space 2 Administrative prohibition For Cease message, gives reason for ceasing to be neighbor: 0 Unspecified 1 Going down 2 No longer needed Otherwise, this field MUST be zero. Sequence Number A sequence number to aid in matching requests and replies. NR Hello Interval Minimum Hello polling interval(seconds). NR Poll Interval Minumum NR polling interval(seconds). - 29 - RFC 888 JANUARY 1984 A.2 NEIGHBOR HELLO/I HEARD YOU 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 ! Status ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! Checksum ! Autonomous System # ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! Sequence # ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Description: Exterior neighbors use EGP Neighbor Hello and I Heard You Messages to determine neighbor connectivity. When a gateway receives an EGP Neighbor Hello message from a neighbor it should respond with an EGP I Heard You message. EGP Version # 2 Type 5 Code Code = 0 for Hello Code = 1 for I Heard you Checksum The EGP checksum is the 16-bit one's complement of the one's complement sum of the EGP message starting with the EGP version number field. For computing the checksum, the checksum field should be zero. Autonomous System # This 16-bit number identifies the autonomous system containing the gateway which is the source of this message. - 30 - RFC 888 JANUARY 1984 Sequence Number A sequence number to aid in matching requests and replies. Status 0 No status given 1 You appear reachable to me 2 You appear unreachable to me due to neighbor reachability protocol 3 You appear unreachable to me due to network reachability information (such as 1822 "destination dead" messages from ARPANET) 4 You appear unreachable to me due to problems with my network interface - 31 - RFC 888 JANUARY 1984 A.3 NR POLL 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: A gateway that wants to receive an NR message from an Exterior Gateway will send an NR Poll message. Each gateway mentioned in the NR message will have an interface on the network that is in the IP source network field. EGP Version # 2 Type 2 Code 0 Checksum The EGP checksum is the 16-bit one's complement of the one's complement sum of the EGP message starting with the EGP version number field. For computing the checksum, the checksum field should be zero. Autonomous System # This 16-bit number identifies the autonomous system - 32 - RFC 888 JANUARY 1984 containing the gateway which is the source of this message. Sequence Number A sequence number to aid in matching requests and replies. IP Source Network Each gateway mentioned in the NR message will have an interface on the network that is in the IP source network field. The IP source network is coded as one byte of network number followed by two bytes of zero for class A networks, two bytes of network number followed by one byte of zero for class B networks, and three bytes of network number for class C networks. - 33 - RFC 888 JANUARY 1984 A.4 NETWORK REACHABILITY 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 ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! Checksum ! Autonomous System # ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! Sequence # ! # of Int Gwys ! # of Ext Gwys ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! 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 ! - 34 - RFC 888 JANUARY 1984 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! net n,2,1 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ; 1, 2 or 3 bytes +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! net n,2,2 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ; 1, 2 or 3 bytes +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... Description: The Network Reachability message (NR) is used to discover which networks may be reached through Exterior Gateways. The NR message is sent in response to an NR Poll message. EGP Version # 2 Type 1 Code 0 Checksum The EGP checksum is the 16-bit one's complement of the one's complement sum of the EGP message starting with the EGP version number field. For computing the checksum, the checksum field should be zero. Autonomous System # This 16-bit number identifies the autonomous system containing the gateway which is the source of this message. U (Unsolicited) bit This bit is set if the NR message is being sent unsolicited. - 35 - RFC 888 JANUARY 1984 Sequence Number The sequence number of the last NR poll message received from the neighbor to whom this NR message is being sent. This number is used to aid in matching polls and replies. IP Source Network Each gateway mentioned in the NR message will have an interface on the network that is in the IP source network field. # of Interior Gateways The number of interior gateways that are mentioned in this message. # of Exterior Gateways The number of exterior gateways that are mentioned in this message. Gateway IP address 1, 2 or 3 bytes of Gateway IP address (without network #). # of Distances The number of distances in the gateway block. Distance The distance. # of Nets The number of nets at this distance. Network address 1, 2, or 3 bytes of network address of network which can be reached via the preceding gateway. - 36 - RFC 888 JANUARY 1984 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: An EGP Error Message is sent in response to an EGP Message that has a bad checksum or has an incorrect value in one of its fields. EGP Version # 2 Type 8 Code 0 Checksum The EGP checksum is the 16-bit one's complement of the one's complement sum of the EGP message starting with the EGP version number field. For computing the checksum, the checksum field should be zero. Autonomous System # - 37 - RFC 888 JANUARY 1984 This 16-bit number identifies the autonomous system containing the gateway which is the source of this message. Sequence Number A sequence number assigned by the gateway sending the error message. Reason The reason that the EGP message was in error. The following reasons are defined: 0 - unspecified 1 - Bad EGP checksum 2 - Bad IP Source address in NR Poll or Response 3 - Undefined EGP Type or Code 4 - Received poll from non-neighbor 5 - Received excess unsolicted NR message 6 - Received excess poll 7 - Erroneous counts in received NR message 8 - No response received to NR poll - 38 - ⌨️ 快捷键说明
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