From: Justin Menga (Justin.Menga@xxxxxxxxxxxxxxxxxx)
Date: Wed Feb 07 2001 - 06:41:54 GMT-3
Hi Chuck,
I just tested your theory - doesn't sound right - I had a connected network
configured as a default-network, no static or default routes - this was
propagated to other IGRP neighbors.........
You do have to wait for the next IGRP update for this change to propagate -
or you can 'clear ip route *'
Regards,
Justin Menga CCIE #6640 MCSE+I CCSE
WAN Specialist
Computerland New Zealand
PO Box 3631, Auckland
DDI: (+64) 9 360 4864 Mobile: (+64) 25 349 599
mailto: justin.menga@computerland.co.nz
-----Original Message-----
From: Chuck Larrieu [mailto:chuck@cl.cncdsl.com]
Sent: Wednesday, 7 February 2001 6:49 p.m.
To: CCIE_Lab Groupstudy List
Subject: Default routes and default networks - some experiments
Trying to pare down my inbox by getting rid of threads I have saved for
experimentation. This one has me, and I am ashamed to admit it, but I can't
figure out why.
ISIS domain ----------------------------- Other Protocol Domain
Ip route 0.0.0.0 0.0.0.0 --> <- default route or default network depending
Ok, work out the bugs in my design. Everything is what it should be. Now
then....
When "other domain" is RIP and I do a default-information originate, I can
ping all over the place and life is good.
Same thing when "other domain" is OSPF
But when "other domain" is IGRP, life is hell. Pings go nowhere. I can get
to the other side of the connection to the ISIS domain but not beyond. I can
get from the ISIS domain to the other edge of the IGRP domain but not
beyond. The candidate default route is in all of the IGRP router routing
tables.
Same when "other domain" is EIGRP
No changes were made on the ISIS side of the fence during any of these
tests.
I conclude that the problem is my misunderstanding of the ip default-network
mechanism. Until this moment, I had believed that all that was required was
that the default network be part of the routing process and appear in the
routing table. This does not appear to be true. I am certain this is not a
classful / classless issue because I am only using classful networks
Well, a bit of research, and here is what I come up with. I don't like it,
if for no other reason than it has been said here and elsewhere that this is
grounds for losing points in the Lab:
If the default network is a directly connected network, then the router
itself still needs a default route.
So, you must have an ip route 0.0.0.0 0.0.0.0 [network]
And then an ip default-network [network]
Only in this manner can (E)IGRP then propogate the default.
This also explains why my grand WAN in the brokerage firm actually worked
the way it was supposed to, even though I was running EIGRP. I had the
0.0.0.0 0.0.0.0 static on each and every router.
Obviously there are ways around this. Route maps of various flavors. Policy
routing of varying degrees of cleverness. But this is one hell of a "gotcha"
/ "pitfall"
60 days and counting :-O oh my!
Chuck
A long shot at passing is better than no shot.
Right now that's all I got to get me through,
So I gotta believe!
( paraphrased from Kathy Baille / Baille and the Boys
a song from several years ago )
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