My friends,
Please, allow me to join.
The gotcha with conditional default route injection into OSPF is that the route-map is used by the OSPF IOS code only in a very limited way: It only supports the "match ip address" and "match ip address prefix-list" to specify networks whose presence will be verified in the RIB. What's even more, it doesn't work by filtering the whole routing table through the route-map to see if there are any matches, rather, it is done in the reverse way: Line by line, the referenced ACL or prefix-list entries will be treated as network/netmask combinations and looked up in the RIB. While this is obviously way more efficient than pouring the entire routing table through that route-map, it also means that the ACL or prefix-list must express only exact network/netmask matches to look for, because the entries in those lists must be convertible into a plain network/netmask values. It is thus not possible to use fancy wildcard masks in the ACL, or the "ge" and "le" operators in prefix lists to encode entire sets of networks to look for.
The "match track" reference in the route-map is completely ignored by the IOS OSPF code so it doesn't have any effect.
@Stephan Lache , you can still accomplish what you need to do but you need to do it indirectly: Install a "dummy" static indicator route into your routing table whenever the SLA probe is successful, and use the route-map for the default route to check this indicator route. This should work nicely.
So the configuration would be similar to this; I assume that the IP SLA and the track object 1 are already configured the way you had them previously.
ip route 192.0.2.255 255.255.255.255 Null0 track 1
!
ip prefix-list TrackRoute permit 192.0.2.255/32
!
route-map CheckTrackRoute permit 10
match ip address prefix-list TrackRoute
!
router ospf 1
default-information originate metric-type 1 route-map CheckTrackRoute
Please give it a try!
By the way, "match track" line in a route-map truly refers to the track object state, not existence (what would be the point to verify whether a track object is configured or not?), but just for OSPF, its use just isn't supported.
Regarding the use of the "always" keyword - this one has two effects, really:
1) Removes the requirement for the default route to be in the RIB before the router originates its own default route into OSPF
2) Prevents the OSPF process from installing learned default routes from other OSPF routers into the RIB
When combined with a route-map, the "always" keyword removes the check for the default route in the RIB (if that one is required, the route-map can still check it itself) but the second effect - preventing the OSPF process from installing a learned default route from other OSPF speakers in the same AS - still remains.
Best regards,
Peter
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