Computer Networking Problems and Solutions by Russ White Ethan Banks & Ethan Banks

Author:Russ White,Ethan Banks & Ethan Banks
Language: eng
Format: epub
Publisher: Pearson Education Limited (US titles)
Published: 2018-06-15T00:00:00+00:00

The Routing Information Protocol

The Routing Information Protocol (RIP) was originally specified in RFC1058, Routing Information Protocol, published in 1998.2 The protocol was updated in a series of more recent RFCs, including RFC2435, RIP version 2,3 and RFC2080, RIP Next Generation for IPv6.4 Figure 15-7 is used to explain RIP operation.

Figure 15-7 RIP Operation Example

The operation of RIP is deceptively simple. In Figure 15-7:

1. A discovers 2001:db8:3e8:100::/64 because it is configured on a directly attached interface.

2. A adds this destination to its local routing table with a cost of 1.

3. As 100::/64 is installed in the local routing table, A will advertise this reachable destination (route) to B and C.

4. When B receives this route, it will add the cost of the inbound interface so that the path through A has a cost of 2, and examine its local table for any lower-cost routes to this destination. As B has no other path to 100::/64, it will install the route in its routing table and advertise the route to E.

5. When C receives this route, it will add the cost of the inbound interface so that the path through A has a cost of 2, and examine its local table for any lower-cost routes to this destination. As C has no other path to 100::/64, it will install the route in its routing table and advertise the route to D and E.

6. When D receives this route, it will add the cost of the inbound interface from C so that the path through C has a cost of 3, and examine its local table for any lower-cost routes to this destination. As D has no other path to 100::/64, it will install the route into its routing table and advertise the route to E.

7. E will now receive three copies of the same route; one through C with a cost of 3, one through B with a cost of 4, and one through D with a cost of 5. E will choose the path through C with a cost of 2, installing this path to 100::/64 into its local routing table.

8. E will not advertise any path to 100::/64 toward C, because it is using C as its best path to reach this specific destination. Thus, E will split horizon its advertisement of 100::/64 toward C.

9. While E will advertise its best path, through C, to both D and B, neither will choose the path through E, as they already have better paths available toward 100::/64.

RIP advertises a set of destinations and costs one hop at a time through the network; hence it is considered a distance vector protocol. The process that RIP uses to find a set of loop-free paths through the network is considered a distributed form of the Bellman-Ford algorithm, but it is not obvious how the process that RIP is using is related to Bellman-Ford.

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