OSPF: distribute-list <acl> out FastEthernet<x>?

[michael.whittle]

I had a strange OSPF problem the other night. I needed to apply an outbound OSPF distribute-list on a set of routers.

I created a standard ACL with the networks I wanted to filter. I then went into the OSPF process and put in:

e.g.

distribute-list 50 out FastEthernet0/0

It came back with a message saying that you can't specify an outbound interface in OSPF. I found this very strange. I tried the same command on a few routers with different models and IOS versions and all of them seemed to do it. I checked the interface and it was OSPF enabled.

The problem I have is that I have two FastEthernet interfaces on the CPE and I need to send the updates out the one interface but not the other. If I can't specify which interface to apply the distribute-list to then it filters for all interfaces.

The only way I can see this working is if you create two OSPF processes and put each interface into a separate process. That just seems like a real hack and messy.

Has anyone every come across this before? Surely there is something you can do to get this functionality working?

Regards,

Mike

[pkhatri · Accepted solution]

Mike,

That is perfectly okay behaviour. One of the premises around which OSPF (link-state protocols in general) are built is that all routers in an area must have the same LSAs. Using something like an interface-specific outbound distribute-list would violate this principal.

If there are routers in the network that you don't want a certain OSPF route on, one option may be to apply a non-interface-specific inbound distribute-list on those routers that deny those routes. That will result in the routes not getting installed in the routing table, but will not tamper with the LSAs.

Pls do remember to rate posts.

Paresh

[michael.whittle]

That makes sense. Kind of obvious if you think about it. Just didn't occur to me at the time. Thanks a lot.

[olorunloba]

Which IOS are you using? Can you change the IOS?. It might be an IOS issue. However, note that you can not filter out Inter and Intra area routes.

http://www.cisco.com/en/US/tech/tk365/technologies_q_and_a_item09186a0080094704.shtml#q12