| date | ospf_tag | tags | title | url | |
|---|---|---|---|---|---|
2007-10-30 07:29:00 +0100 |
details |
|
More Details on OSPF Route Filters |
/2007/10/more-details-on-ospf-route-filters.html |
I did a few follow-up tests with the distribute-list in OSPF configuration command and stumbled across a few interesting facts (IOS release 12.4(15)T1 on a 3725 platform):
- Although the router allows you to configure distribute-list acl in interface, it does not work. Routes received through that interface (or having the interface as the next-hop) are not filtered.
- When you apply the distribute-list in command, the routing table is not changed. Clearing the IP routing table does not help, you have to clear ALL OSPF processes (including bringing down all OSPF adjacencies) with the clear ip ospf process command for the route filter to take effect.
- The same limitations don't apply in the other direction: when you remove the distribute-list in, SPF is triggered and the routes appear in the IP routing table automatically.
- The somewhat undocumented gateway option of the distribute-list in command works, but not quite as I would expect: the IP next hop, not the router-ID of the router advertising the IP prefix is matched by the prefix-list.
And, last but not least, I've lab-verified my previous claim: applying the distribute-list in on a transit router can result in a black hole, as the LSAs themselves are not filtered.