📄 rfc827.txt
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1 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. - 35 - RFC 827 Bolt Beranek and Newman Inc. Eric C. Rosen 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 Last Poll Id Number The identification number of the most recently received NR poll message from the neighbor to which this message is being sent. Minimum Polling Interval This gateway should not be polled for NR messages more often than once in this number of minutes. - 36 - RFC 827 Bolt Beranek and Newman Inc. Eric C. Rosen 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 # ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! IP Source Network ! Interval ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! Identification # ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 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 # 1 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 containing the gateway which is the source of this message. - 37 - RFC 827 Bolt Beranek and Newman Inc. Eric C. Rosen Identification Number An identification 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. Interval The polling interval in minutes. - 38 - RFC 827 Bolt Beranek and Newman Inc. Eric C. Rosen 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 # ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! Fragment # !# of last frg. ! Identification # ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! IP Source Network ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! # of Int Gwys ! # of Ext Gwys ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! # 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! distance ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! net 1,2 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ; 1, 2 or 3 bytes +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! distance ! +-+-+-+-+-+-+-+-+ . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! net 1,m !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ; m nets reachable +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ; via Gateway 1 . . +-+-+-+-+-+-+-+-+ ! # of nets ! ;number of nets for Gateway n +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! Gateway n IP address (without network #) ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! net n,1 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ; 1, 2 or 3 bytes +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! distance ! +-+-+-+-+-+-+-+-+ - 39 - RFC 827 Bolt Beranek and Newman Inc. Eric C. Rosen +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! net n,2 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ; 1, 2 or 3 bytes +-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! distance ! . +-+-+-+-+-+-+-+-+ . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! net n,m !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ; m nets reachable +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ; via Gateway n ! distance ! +-+-+-+-+-+-+-+-+ - 40 - RFC 827 Bolt Beranek and Newman Inc. Eric C. Rosen 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 # 1 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. Identification Number The identification 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. Fragment Number Which Fragment this is in the NR Message. Zero, if fragmentation is not used. - 41 - RFC 827 Bolt Beranek and Newman Inc. Eric C. Rosen Number of Last Fragment Number of the last fragment in the NR Message. Zero, if fragmentation is not used. 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. # of Networks The number of networks for which the gateway whose IP address immediately follows is the appropriate first hop. Gateway IP address 1, 2 or 3 bytes of Gateway IP address (without network #). Network address 1, 2, or 3 bytes of network address of network which can be reached via the preceding gateway. Distance 1 byte of distance in # of hops. - 42 - RFC 827 Bolt Beranek and Newman Inc. Eric C. Rosen 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 # ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! Error Type ! Error Code ! Id. # of Erroneous Msg. ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! Sequence # ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 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 # 1 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 # This 16-bit number identifies the autonomous system containing the gateway which is the source of this message. - 43 - RFC 827 Bolt Beranek and Newman Inc. Eric C. Rosen Sequence Number A sequence number assigned by the gateway sending the error message. Error Type The Type of the EGP message that was in error. Error Code The Code of the EGP message that was in error. Identification number of erroneous message The Sequence number of the EGP message that was in error. 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 ex⌨️ 快捷键说明
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