Troubleshooting IP routing protocols


I would like to know about troubleshooting IP routing protocols in general and RIP in particular.

Some info on troubleshooting techniques would help. Also, in a network of about 12 RIP routers if a route is flapping in one of the routers, what would be symptoms to look out for (how do i know if routes are flapping)? What would be remedial action.? Appreciate your valuable reply.

Thanks, syuga

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A route flap can often come from an interface flap which then makes the route come from another path or router from an endpoint perspective. The bottom line is that show ip route and show ip protocol are your best friends, and you need to isolate the flaps back to a source device and time so you can isolate the issue. You can also debug to help see the rip messages.

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I think the place to start would be sh ip route

From "R [120/1] via, 00:00:08, Tunnel0"

I think that this shows the age of the route and the interface it was learned on. With a bit of luck the age will not be updated with each RIP update:) so any flaps will be evident in short route age times.

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If your routers are sufficiently beefy (and I think anything is, these days unless you have hundreds of routes which are flapping, and you'd probably already have noticed the CPU load from that or lots of very short ages in the routing table above) then the next thing I'd do would be 'debug ip routing', but do it carefully. Make sure the router isn't logging to the console. Open two telnet or ssh connections, do a 'term mon' on one of them and issue 'debug ip routing' on the other. Be ready with 'no debug ip routing' in case you need it quickly! 'show ip route w.x.y.z [m.n.p.q]' can also be useful.



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