From: Bryan Ginman (ginmanb@xxxxxxxxxxx)
Date: Sat Nov 10 2001 - 18:01:48 GMT-3
Doyle has a great example (modifying distance) of this in Vol. 1 on pg 791.
Excellent for optimal routing with redundancy for mutual redistribution.
Cheers,
Bryan Ginman
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Ben-Shalom, Omer
Sent: Saturday, November 10, 2001 2:35 PM
To: ccielab@groupstudy.com
Subject: Idea on easy safe redistribution - looking for opinions
Most protocols support route tags which are very useful in creating filters
to stop route feedback in a way that is self maintaining unlike specific
route maps or distribute lists which include specific routes.
Still - when distributing into a protocol that does not support tags (I
believe IGRP is one) you cannot then use a tag to limit routes coming back.
Route feedback is not really a problem when a source with a higher
administrative distance is feeding into one with lower distance as the
routes are less preferred but can be a real problem when fed from a lower
admin distance (more preferred) source to a higher admin distance (less
preferred) source.
Following this logic If I change IGRP admin distance to, say 117 to place
before RIP but after all the protocols that support route tags and then use
a route map to tag routes from IGRP to (say) OSPF and another route map to
block this tag redistributing back to IGRP am I all done with regard to the
mutual redistribution ? (I assume I can in general now ignore the feedback
from IGRP to OSPF on the grounds that OSPF routes are preferred due to the
admin distance change).
If there are no major holes you see in this then this is a few lines of
route-maps that do not need to be changed at any time in the lab and still
solve the feedback issue.
I am interested in any comments, especially if you find a problem.
PS - I can think of one problem myself and that is an ISDN on demand
circuit, even just getting a type 5 LSA for the link into the OSPF process
can keep the line up indefinitely but then I can live with filtering this
one specific route as well.
Thanks
Omer.
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