From: Cagri Yucel (cyucel@gmail.com)
Date: Mon May 07 2007 - 12:33:37 ART
Hi Greg, To be honest in your scenario you don't need to do anything, since
EIGRP has its own prevention mechanism against this. AD 90 vs 170. So you
will be safe.
A question arises if you have more protocols being advertised into EIGRP, so
other EIGRP router will prefer the OSPF route with 110 against this 170
root. This is not a loop but suboptimal routing. Best approach is to tweak
distances for the networks redistributed into EIGRP.
I don't have a rule of thumb, I just put the diagram on the table and check
what happens to every route travelling through the infrastructure.
HTH
On 5/7/07, Gregory Gombas <ggombas@gmail.com> wrote:
>
> Hello Group,
>
> I was wondering if someone can post some guidelines or suggest
> recommended reading regarding route redistribution and preventing
> route loops?
>
> I understand there are two main techniques used to preventing route
> feedback:
> 1. Use route maps to deny tagged routes from being fed back into the
> same routing domain.
> 2. Change the administrative distance on selected routes to prefer
> routes learned from one source over another.
>
> I'm not always sure which method to use for a given scenario.
>
> For instance I was recently working on IE Lab 2 where you have the
> same EIGRP AS connecting to an OSPF backbone like so:
>
> EIGRP
> | \
> OSPF |
> | /
> EIGRP
>
> Normally when I have more than one point of redistribution I
> immediately configure route maps to tag and deny routes from being fed
> back. In this scenario, however, tagging the EIGRP routes on one end
> causes them to be denied on the other end (as is the case when the
> link connecting the EIGRP networks goes down and its forced through
> the OSPF backbone). I had to tweak the administrative distance on a
> few routers to get this working.
>
> So my questions is, is there a general rule of thumb regarding what
> type of scenario requires AD tweaking versus route tagging?
>
> Thanks,
> Greg
>
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-- -cagri
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