From: Scott Morris (smorris@ipexpert.com)
Date: Mon May 07 2007 - 12:50:00 ART
In basic redistribution it may not make any difference. But when you are
going from protocol 1 into protocol 2 and THEN into protocol 3, you may find
you are redistributing things you don't want to, and increasing the
difficulty of your scenario.
Tags are just a nice way to pick and choose specific routes without needing
to think about AD or multi-hop protocol stuff. In two-protocol scenarios
like you lay out, AD can be a perfectly acceptable way.
Just make sure you are not surprised by anything. THAT is the most
important part! (Debug ip routing is a great command to use)
Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713, JNCIE
#153, CISSP, et al.
CCSI/JNCI-M/JNCI-J
IPexpert VP - Curriculum Development
IPexpert Sr. Technical Instructor
smorris@ipexpert.com
http://www.ipexpert.com
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Gregory Gombas
Sent: Monday, May 07, 2007 10:57 AM
To: Cisco certification
Subject: Redistribution - When to use route tags vs administrative distance?
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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