Any other way to..

I would think an inbound route-map on the ABR that denies metric-types 1 and

-ja

AFAIR external routes are not filtered within OSPF - ie you cannot stop them propagating via the OSPF database between routers. So filtering at the ABR would alter the routing table on the ABR, but not stop those type 5 external routes propagating between areas.

often the easiest way is to make sure they are not type 5 in the 1st place - Try using "passive interface" so a local route is OSPF rather than static, but prevent the source router forming an adjacency on the subnet. Or aggregate a bunch of statics at the point they get injected into OSPF using route maps.

Have a look at NSSA areas - but cannot remember if they give you much control of externals.

could you elaborate a little more on your suggestion? I have a main router in area 0 with static routes and I want to prevent them from traversing through the ABR. I need adj between all routers.

use BGP to carry the static if there are a lot of them - if not them do not worry about it

thanks Merv. Still curious about this though.

Try using "passive interface" so a local route is OSPF rather than static, but prevent the source router forming an adjacency on the subnet.

a snippet would be great.

could you elaborate a little more on your suggestion? I have a main router in area 0 with static routes and I want to prevent them from traversing through the ABR. I need adj between all routers.

Perhaps running two OSPF processes on the ABR and controlling via redistribution which routes are passed between area 0 and the non-0 area will work for you. Be careful not to send routes received from area 0 and passed into the non-0 area, back towards area 0.....

-ja

passive will only work for external routes from "connected" interface srouces.

you have 2 places to filter an external route from a static in OSPF directly - where it enters the OSPF domain, and when it drops out of OSPF into a routing table.

So you can stop your statics going into OSPF entrirely, or stop them getting into the routing table on other routers - but since OSPF replicates externals via the database, you would have to do that at each router.

the other way is that exernals do not cross into a stub (totally stubby area in cisco speak) or NSSA area.

So all externals within OSPF get aggregated into 1 default route if you set the area up as totally stubby or NSSA.

However - why filter like this? i have a customer network with 3k internal routes, where many are externals (and since almost all is dual routers in parallel, there are 2 copies of each external in the database).

Not much overhead for route propagation, processing or bandwidth.

OSPF design guide on the cisco site may be useful: