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Sidewinder G2 6.1.2 Administration Guide - Glossary of Technical ...

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Appendix D: Configuring Dynamic Routing with RIP<br />

RIP with standard IP routers<br />

RIP with<br />

standard IP<br />

routers<br />

614<br />

Figure 247: Dynamic<br />

routing a with standard IP<br />

route<br />

The following describes how RIP processing aids in routing IP packets through<br />

a network that has a redundant routing architecture. Figure 247 illustrates this<br />

redundant architecture.<br />

Security Alert: RIP version 1 is an inherently insecure protocol. Without careful<br />

configuration <strong>of</strong> this service, this system may be susceptible to route confusion<br />

attacks.<br />

Bizco<br />

Network<br />

Telnet server<br />

R<br />

router_a<br />

router_b<br />

CorpCity<br />

Network<br />

Note: This figure assumes that all routers (a, b, c, and d) are exchanging RIP<br />

packets between each other every 30 seconds.<br />

In this example, it is unnecessary for the Telnet server and the client to be<br />

accepting RIP packets. The server can statically configure its gateway to be<br />

Router_a. The client can statically configure its gateway to Router_b.<br />

The Telnet client has two different possible paths <strong>of</strong> reaching the server: (1) via<br />

Router_b-to-Router_a, and (2) via Router_d-to-Router_c-to-Router_a.<br />

Examining the routing table on Router_b, you would find that there are two<br />

possible routes to the Bizco network, one with a hop count equal to two<br />

(through Router_a), the other with a hop count to three (through Router_d).<br />

When the Telnet client needs to connect to the Telnet server, it sends a TCP<br />

connection request to Router_b because its internal default route points to<br />

Router_b. Router_b receives the connection frame and because the route to<br />

the Bizco network is shorter via Router_a (two hops verses three hops), it<br />

forwards the connection frame on to Router_a. Router_a forwards the frame<br />

into the Bzco network and it eventually gets received by the Telnet server. The<br />

Telnet server builds and sends a reply frame back, this frame typically follows<br />

the same route back to the client. The two systems have established a<br />

connection.<br />

The dynamic routing capability <strong>of</strong> RIP can be seen when the link between<br />

Router_a and Router_b is lost. As soon as Router_b notices that it is no longer<br />

receiving RIP updates from Router_a, it updates its local routing table hop<br />

count for that route to 16 (route unreachable) and broadcasts this to others on<br />

its local network (this is to notify Router_d).<br />

R<br />

R<br />

router_c<br />

R<br />

Telnet<br />

client<br />

router_d

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