TCP IP Illustrated

There are many subtle details in the implementation

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Unformatted text preview: sured in minutes. During this settling time routing loops can occur. There are many subtle details in the implementation of RIP that must be followed to help prevent routing loops and to speed convergence. RFC 1058 [Hedrick 1988a] contains many details on how RIP should be implemented. The use of the hop count as the routing metric omits other variables that should be taken into consideration. Also, a maximum of 15 for the metric limits the sizes of networks on which RIP can be used. Example We'll use the program ripquery, which is available from the gated distribution, to query some routers for their routing table, ripquery tries to send one of the undocumented requests (named "poll," a command of 5 from Figure 10.3) to the router, asking for its entire routing table. If no response is received in 5 seconds, the standard RIP request is issued (command of 1). (Earlier we said a request with the family set to 0 and the metric set to 16 asks the other router for its entire routing table.) Figure 10.5 shows the two routers that we'll query for their routing table from the host sun. If we execute ripquery from sun, fetching the routing information from its next-hop router, netb, we get the following: sun % ripquery -n netb 504 bytes from netb (, metric 1, metric 1 244 bytes from netb ( first message contains 504 bytes lots of other lines deleted the top Ethernet in Figure 10.5 the bottom Ethernet in Figure 10.5 second message with remaining 244 bytes lots of other lines deleted As we expect, the metric for our subnet that is announced by netb is 1. Additionally, the top Ethernet that netb is also attached to ( has a metric of 1. (The -n flag says to file:///D|/Documents%20and%20Settings/bigini/Docu.../homenet2run/tcpip/tcp-ip-illustrated/dynamic.htm (6 of 17) [12/09/2001 14.46.53] Chapter 10. Dynamic Routing Protocols print the IP addresses numerically instead of trying to look up the names.) In this exam...
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This test prep was uploaded on 04/04/2014 for the course ECE EL5373 taught by Professor Guoyang during the Spring '12 term at NYU Poly.

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