From: Le Dinh An (anld@ispco.com.vn)
Date: Wed Feb 12 2003 - 05:38:46 GMT-3
Hello Hunt,
I wonder how this can happen, where is split horizon?
Hunt Lee wrote:
>Hello group,
>
>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
>.
>
>--
>WebCentral Pty Ltd Australia's #1 Internet Web Hosting Company
>Level 1, 96 Lytton Road. Network Operations - Systems Engineer
>PO Box 4169, East Brisbane. email: huntl@webcentral.com.au
>Queensland, Australia. phone: +61 7 3249 2553
>.
-- Le Dinh An Network Consultant Phone: 84 913 100 478 .
This archive was generated by hypermail 2.1.4 : Sat Mar 01 2003 - 11:06:19 GMT-3