Conditional Advertising - OSPF default-inf orig route-map

Hi, i've been trying to get my head around conditional advertising using
route maps. So here is the scenario in regards to OSPF.

1. Advertise a default route given the presence of 1.1.1.0/24 and
2.2.2.0/24 in the routing table.

This is easy enough, using a single ACL with both routes listed. This way
as long as EITHER one of the routes is in the routing table, the default
route is advertised. When both routes go away, the default advertisement
stops.

The confusion comes in when I try to get the default advertisement to stop
when EITHER of the 2 routes disappears. This doesnt seem to work
regardless of what combo of route-map and ACL I use.
My understanding of route-map AND/OR algorithm is that if you have a single
match statement with multiple elements, (e.g. match ip add 1 2) this is a
logical OR. A route-map with multiple match statements (e.g. route-map x
per 10 match ip add 1; route-map x per 20 match ip add 2) is a logical
AND. A route-map with a single match clause and element with multiple
lines (match ip add 3) is a logical OR.

Assuming ACLs are:
access-l 1 per 1.1.1.0 0.0.0.255
access-l 2 per 2.2.2.0 0.0.0.255
access-l 3 per 1.1.1.0 0.0.0.255
access-l 3 per 2.2.2.0 0.0.0.255

Regardless of how I construct my route-map and ACL combo, the default route
is advertised by OSPF as long as EITHER the 1.1.1.0/24 or 2.2.2.0/24 is
present in the routing table. Could you guys please help me understand this
a little better?

Thanks in advance,
Don

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Received on Thu Dec 10 2009 - 16:29:53 ART