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what is routingloop and how it occures in routing? how can i implement in my lab?


Community Member

Re: Routing

You have 2 types of routing loops.

The first loops the traffic and the other loops the routing table entries themselves.

A traffic loop is easy to do.

Just put in the same static route in 2 routers and point them to each other.

For example

If you have router A with ip address and router b wiht ip address

In router A put in

IP route

in router b put in

ip route

now ping from either router.

A routing loop of the routing table itself is very complex to simulate and very hard to fix.

Basically it is caused by route redistribution on multiple routers. A single routing protocol is smart enough to know that I do not want to learn a route that I just sent to another router. When you convert routes from one routing protocol to another some of this information is lost.

For this second kind of loop you need a good understatnding of administative distance. I do not have a simple example of how to do this since it in most cases will require 3 or 4 routers to get loop that will be of any interest to look at.

Community Member

Re: Routing


A routing loop comes from error in your routing configuration. For example if you have two routers connected together A and B and that A beleives that subnet X is reachable via B and B beleives that the subnet X is reachable via A, a packet destinated to X will loop between A and B until its TTL reaches 0.

These loop comes often from redistribution between different routing process with some misconfiguration. The following document shows some example:

However the easiest way to get a routing loop in your lab is to configure static routes :


ip route X.X.X.X B.B.B.B


ip route X.X.X.X A.A.A.A

Please rate if it helps.



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