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IEWBv4 Lab 7 – Continued

Posted by Jo on October 27, 2007

I finished off the redistribution section of this lab. One of the interesting tasks in this section revolved around traffic engineering paths from SW2 that had 2 interfaces in the RIP routing domain. These routes were learnt from 2 separate interfaces on SW2, so by default were being preferred out of Fa0/20. The task wanted a subset of these routes to take the best path through the network, and Fa0/20 wasnt the optimal path for these.
The solution was to use an offset-list on each of the two RIP enabled interfaces to specify modify the metric for these routes.

First we need to match the routes that we want to control via an access list.

access-list 1 permit
access-list 1 permit
access-list 1 permit
access-list 1 permit
access-list 1 permit
access-list 1 permit

Then within the RIP process apply the offset-list to each interface.

router rip
offset-list 1 in 2 FastEthernet0/20
offset-list 0 in 1 FastEthernet0/21

In this example the first offset-list applied to Fa0/20 matches access-list 1 and bumps up the metric by 2.The 2nd offset-list matches all traffic (this is what the 0 specifies) and increases the metric by 1. This had the effect that all routes specified in access-list 1 were then preferred by RIP on Fa0/21 due to the metric being higher on Fa0/20. All other routes were preferred out of Fa0/21 as they had the lower RIP metric. I struggled a bit with this task initially as I didnt have RIP running on the interface connected to F0/20 on SW2 (in this case R3), so to start with I was seeing all traffic going out of Fa0/21 by default. After I debugged it and saw there were no routes coming in via F0/20 I checked my config on R3 and enabled RIP on the correct interface and it started to work as expected. This is another example of double checking things better before moving onto the next task, as I wasted too long working this out!


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