From: Hunt Lee (ciscoforme3@yahoo.com.au)
Date: Tue Feb 11 2003 - 10:53:21 GMT-3
Since IS-IS doesn't have "distribute-list" command, is there any other commands /
ways that I could use to block / filter routes from coming into an ISIS router?
The lab scenario that stir up my thinking was:-
R1 --------- R2 ---------- R3 -------- 172.18.3.3/32 (lo0)
ISIS RIPv1
I need to get this Loopback route to R1.
To do this, I redistribute the RIP route into ISIS at R2. Now an issue arises,
since ISIS has a lower admin dist than RIP, R2 now has a routing loop for
172.18.3.3/32. This minute it gets the route from R3 (thru RIP), & the next minute
it gets the same route from R1 (thru ISIS).
Feb 11 22:50:49.547 UTC: RT: add 172.18.0.0/16 via 172.17.23.2, rip metric [120/1]
Feb 11 22:50:57.563 UTC: RT: closer admin distance for 172.18.0.0, flushing 1 routes
Feb 11 22:50:57.563 UTC: RT: add 172.18.0.0/16 via 172.16.12.1, isis metric [115/73]
Feb 11 22:51:07.563 UTC: RT: delete route to 172.18.0.0 via 172.16.12.1, isis metric
[115/73]
Feb 11 22:51:07.563 UTC: RT: no routes to 172.18.0.0
Feb 11 22:51:07.563 UTC: RT: delete network route to 172.18.0.0
Feb 11 22:51:16.603 UTC: RT: add 172.18.0.0/16 via 172.17.23.2, rip metric [120/1]
Feb 11 22:51:24.615 UTC: RT: closer admin distance for 172.18.0.0, flushing 1 routes
Feb 11 22:51:24.615 UTC: RT: add 172.18.0.0/16 via 172.16.12.1, isis metric [115/73]
Feb 11 22:51:34.615 UTC: RT: delete route to 172.18.0.0 via 172.16.12.1, isis metric
[115/73]
Feb 11 22:51:34.615 UTC: RT: no routes to 172.18.0.0
Feb 11 22:51:34.615 UTC: RT: delete network route to 172.18.0.0
The only way I found so far is to lower the admin dist for that particular route
coming from R3.
router rip
network 172.17.0.0
network 172.19.0.0
distance 110 172.17.23.2 0.0.0.0 block
ip access-list standard block
permit 172.18.0.0 0.0.255.255
deny any
Is there any other way I could do this? An alternative is to higher the admin dist
of ISIS routes from R1... but I found that ISIS doesn't allow me to change Admin
Dist per prefix, which makes this option very un-attractive.
Hunt
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