📄 rfc823.txt
字号:
Header Checksum The 16 bit one's complement of the one's complement sum of all 16-bit words in the header. For computing the checksum, the checksum field should be zero. -32- DARPA Internet Gateway September 1982 RFC 823 Source Address The address of the gateway's interface from which the message is sent. Destination Address The address of the gateway to which the message is sent. -33- DARPA Internet Gateway September 1982 RFC 823 ROUTING UPDATE 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ !Gateway Type ! unused (0) ! ; 2 bytes +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! Sequence Number ! ; 2 bytes +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! need-update ! n-distances ! ; 2 bytes +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! distance 1 ! n1-dist ! ; 2 bytes +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! net11 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ; 1, 2 or 3 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ; bytes ! net12 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ; 1, 2 or 3 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ; bytes . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! net1n1 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ; n1 nets at +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ; dist 1 . ... . ; ndist groups +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ; of nets ! distance n ! nn-dist ! ; 2 bytes +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! netn1 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ; 1, 2 or 3 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ; bytes ! netn2 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ; 1, 2 or 3 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ; bytes . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! netnnn !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ; nn nets at +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ; dist n Gateway Type 12 (decimal) Sequence Number The 16-bit sequence number used to identify routing updates. need-update An 8-bit field. This byte is set to 1 -34- DARPA Internet Gateway September 1982 RFC 823 if the source gateway requests a routing update from the destination gateway, and set to 0 if not. n-distances An 8-bit field. The number of distance-groups reported in this update. Each distance-group consists of a distance value and a number of nets, followed by the actual net numbers which are reachable at that distance. Not all distances need be reported. distance 1 hop count (or other distance measure) which applies to this distance-group. n1-dist number of nets which are reported in this distance-group. net11 1, 2, or 3 bytes for the first net at distance "distance 1". net12 second net ... net1n1 etc. -35- DARPA Internet Gateway September 1982 RFC 823 ACKNOWLEDGMENT or NEGATIVE ACKNOWLEDGMENT 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Gateway Type | Unused | Sequence number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Gateway Type Acknowledgments are type 2. Negative acknowledgments are type 10. Sequence Number The 16-bit sequence number that the gateway is acknowledging or negatively acknowledging. -36- DARPA Internet Gateway September 1982 RFC 823 GGP ECHO and ECHO REPLY 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Gateway Type | Unused | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Gateway Type 8 for echo message; 0 for echo reply. Source Address In an echo message, this is the address of the gateway on the same network as the neighbor to which it is sending the echo message. In an echo reply message, the source and destination addresses are simply reversed, and the remainder is returned unchanged. -37- DARPA Internet Gateway September 1982 RFC 823 NETWORK INTERFACE STATUS 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ! Gateway Type ! unused ! +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Gateway Type 9 Source Address Destination Address The address of the gateway's network interface. The gateway can send Net Interface Status messages to itself to determine if it is able to send and receive traffic on its network interface. -38- DARPA Internet Gateway September 1982 RFC 823 APPENDIX B. Information Maintained by Gateways In order to implement the shortest-path routing algorithm, gateways must maintain information about their connectivity to networks and other gateways. This section explains the information maintained by each gateway; this information can be organized into the following tables and variables. o Number of Networks The number of networks for which the gateway maintains routing information and to which it can forward traffic. o Number of Neighbors The number of neighbor gateways with which the gateway exchanges routing information. o Gateway Addresses The addresses of the gateway's network interfaces. o Neighbor Gateway Addresses The address of each neighbor gateway's network interface that is on the same network as this gateway. o Neighbor Connectivity Vector A vector of the connectivity between this gateway and each of its neighbors. o Distance Matrix A matrix of the routing updates received from the neighbor gateways. -39- DARPA Internet Gateway September 1982 RFC 823 o Minimum Distance Vector A vector containing the minimum distance to each network. o Routing Updates from Non-Routing Gateways The routing updates that would have been received from each non-routing neighbor gateway which does not participate in this routing strategy. o Routing Table A table containing, for each network, a list of the neighbor gateways on a minimum-distance route to the network. o Send Sequence Number The sequence number that will be used to send the next routing update. o Receive Sequence Numbers The sequence numbers that the gateway received in the last routing update from each of its neighbors. o Received Acknowledgment Vector A vector indicating whether or not each neighbor has acknowledged the sequence number in the most recent routing update sent. -40- DARPA Internet Gateway September 1982 RFC 823 APPENDIX C. GGP Events and Responses The following list shows the GGP events that occur at a gateway and the gateway's responses. The variables and tables referred to are listed above. o Connectivity to an attached network changes. a. Update the Minimum Distance Vector. b. Recompute the Routing Updates. c. Recompute the Routing Table. d. If any routing update has changed, send the new routing updates to the neighbors. o Connectivity to a neighbor gateway changes. a. Update the Neighbor Connectivity Vector. b. Recompute the Minimum Distance Vector. c. Recompute the Routing Updates. d. Recompute the Routing Table. e. If any routing update has changed, send the new routing updates to the neighbors. o A Routing Update message is received. a. Compare the Internet source address of the Routing Update message to the Neighbor Addresses. If the address is not on the list, add it to the list of Neighbor Addresses, increment the Number of Neighbors, and set the Receive Sequence Number for this neighbor to the sequence number in the Routing Update message. b. Compare the Receive Sequence Number for this neighbor to the sequence number in the Routing Update message to determine whether or not to accept this message. If the message is rejected, send a Negative Acknowledgment message. If the message is accepted, send an Acknowledgment message and proceed with the following steps. -41- DARPA Internet Gateway September 1982 RFC 823 c. Compare the networks reported in the Routing Update message to the Number of Networks. If new networks are reported, enter them in the network vectors, increase the number of networks, and expand the Distance Matrix to account for the new networks. d. Copy the routing update received into the appropriate row of the Distance Matrix. e. Recompute the Minimum Distance Vector. f. Recompute the Routing Updates. g. Recompute the Routing Table. h. If any routing update has changed, send the new routing updates to the neighbors. o An Acknowledgment message is received. Compare the sequence number in the message to the Send Sequence Number. If the Send Sequence Number is acknowledged, update the entry in the Received Acknowledgment Vector for the neighbor that sent the acknowledgment. o A Negative Acknowledgment message is received. Compare the sequence number in the message to the Send Sequence Number. If necessary, replace the Send Sequence Number, and retransmit the routing updates. -42- DARPA Internet Gateway September 1982 RFC 823 REFERENCES [1] Postel, J. (ed.), "Internet Protocol - DARPA Internet Program Protocol Specification," RFC 791, USC/Information Sciences Institute, September 1981. [2] Strazisar, V., "Gateway Routing: An Implementation Specification," IEN-30, Bolt Beranek and Newman Inc., August 1979. [3] Strazisar, V., "How to Build a Gateway," IEN-109, Bolt Beranek and Newman Inc., August 1979. [4] Postel, J., "Internet Control Message Protocol - DARPA Internet Program Protocol Specification," RFC 792, USC/Information Sciences Institute, September 1981. [5] Postel, J., "Assigned Numbers," RFC 790, USC/Information Sciences Institute, September 1981. [6] Littauer, B., Huang, A., Hinden, R., "A Host Monitoring Protocol," IEN-197, Bolt Beranek and Newman Inc., September 1981. [7] Santos, P., Chalstrom, H., Linn, J., Herman, J., "Architecture of a Network Monitoring, Control and Management System," Proc. of the 5th Int. Conference on Computer Communication, October 1980. [8] Haverty, J., "XNET Formats for Internet Protocol Version 4," IEN-158, Bolt Beranek and Newman Inc., October 1980. [9] Mathis, J., Klemba, K., Poggio, "TIU Notebook- Volume 2, Software Documentation," SRI, May 1979. [10] Rosen, E., "Exterior Gateway Protocol," IEN-209, Bolt Beranek and Newman Inc., August 1982. -43- ⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -