Note!
Routers use OSPF configuration from the lab 6.
There are a few filtering methods:
- Ingress filtering using a ‘distribute-list’.
- Ingress filtering using a ‘distribute-list’ with a ‘route-map’.
- Ingress filtering by changing the Administrative Distance of the prefixes to UNKNOWN (255).
- Type 3 LSA filtering using ‘area area-number range’ command (applied on ABR).
- Type 3 LSA filtering using ‘filter-list’ command.
- LSA Flooding Filtering.
The first three methods (1-3) prevent prefixes from entering the routing table. The LSAs are still going to be present in the LSDB since all routers in OSPF area must be synchronized (the same LSDB). These methods are the intra-area filters.
The last three methods (4-6) are inter-area filters preventing LSAs from entering LSDB.
Topology
Task 1
On R3, check the routing table. Make sure that it shows prefixes: 172.16.101.0/24 and 172.16.102.0/24.
Task 2
Configure R3 so prefixes 172.16.101.0/24 and 172.16.102.0/24 do not show in the routing table but show in the LSDB. Do not use distribute-list to accomplish this. Make sure that you match on the router-id of advertising routers.
Task 3
Check the results. Both prefixes in question should be removed from the routing table but should be still seen in the LSDB.
Lab Solution
Task 1
R3 Configuration:
router-id 3.3.3.3
log-adjacency-changes
network 0.0.0.0 255.255.255.255 area 0
distance 255 1.1.1.1 0.0.0.0 FILTER
distance 255 2.2.2.2 0.0.0.0 FILTER
!
Task 3
The prefixes 172.16.101.0/24 and 172.16.102.0 are gone!
