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merging networks

If we aquire a company with network using eigrp 200, and we are using a different autonomous number, would we re-distribute each other eigrp into each other, would we need to use a metric ?

4 REPLIES
Blue

Re: merging networks

on your border router(s), between your two companies, you could use two instances of eigrp until you were able to combine the new company into your existing autonomous system. this plus any redistribution required should work.

this would probably be easiest and should not require any metric changes to make it work.

this does have its drawbacks with requiring twice or more of the resources currently used on your router(s)

if your router(s) did not have the required resources ie: cpu, memory, etc., this could lead to network degredation or in a worst case.....outage.

NOTE: (cisco does not recommend using multiple instances of eigrp with mutual redistribution due to the possibility of discrepancies in the routing table.)

(i've seen it done though in the tight spots where there was no other choice)

please see the following link for more info:

http://www.cisco.com/en/US/tech/tk365/technologies_q_and_a_item09186a008012dac4.shtml#eight

Blue

Re: merging networks

This will work, but with mutual redistribution you should be careful to observe the cardinal rule of redistribution; never allow redistribution of networks back into the protocol that originated them. As an example, if AS1 is all 192.168.X.X and the AS2 is 10.X.X.X you should use route maps to ensure that 192.168.X.X is not redistributed from AS2 to AS1, and that 10.X.X.X is not sent from AS1 to AS2.

Here is a good doc:

http://www.cisco.com/en/US/customer/tech/tk365/technologies_tech_note09186a008009487e.shtml

The redistribution of IGRP/EIGRP into another IGRP/EIGRP process does not require any metric conversion, so there is no need to define metrics or use the default-metric command during redistribution.

Please rate helpful posts.

Community Member

Re: merging networks

Hi

with ref to "As an example, if AS1 is all 192.168.X.X and the AS2 is 10.X.X.X you should use route maps to ensure that 192.168.X.X is not redistributed from AS2 to AS1, and that 10.X.X.X is not sent from AS1 to AS2"

Are you saying that if I redistrubute 1 AS into another AS , the one that is been redistributed in could try and advertise it back to AS 1 where it originated ?

Blue

Re: merging networks

Yes, if you are doing mutual (both ways) redistribution without filtering that is what will happen. This is the most common source of problems with redistribution.

The doc I posted has config examples of using route maps to avoid this.

Avoiding Problems Due to Redistribution

In the section on administrative distance you saw how redistribution can potentially cause problems such as below optimal routing, routing loops, or slow convergence. Avoiding these types of problems is really quite simple?never announce the information originally received from routing process X back into routing process X.

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