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
Check the current routing table on R1. Make sure that it receives both 172.16.104.0/24 and 172.16.144.0/24.
Task 2
Configure R1 so the subnet 172.16.144.0/24 is no longer listed in the routing table. Make sure R1 still has connectivity to 172.16.104.0/24. Use distribute list to accomplish this.
Task 3
Check the results. R1 should have prefix 172.16.144.0/24 in its LSDB but not in the routing table.
Lab Solution
Task 1
Check the current routing table on R1. Make sure that it receives both 172.16.104.0/24 and 172.16.144.0/24.
Configure R1 so the subnet 172.16.144.0/24 is no longer listed in the routing table. Make sure R1 still has connectivity to 172.16.104.0/24. Use distribute list to accomplish this.
R1 Configuration:
router-id 1.1.1.1
log-adjacency-changes
network 10.1.13.1 0.0.0.0 area 0
network 10.1.124.1 0.0.0.0 area 1
network 172.16.101.1 0.0.0.0 area 0
distribute-list 1 in
Task 3
R1 Check:
