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 (4-5) are inter-area filters preventing LSAs from entering LSDB.
Topology
Task 1
On R4, check the routing table. Make sure that it shows prefixes: 172.16.103.0/24 and 172.16.133.0/24.
Task 2
Configure router(s) so the 172.16.103.0/24 and 172.16.133.0/24 are not advertised to R4. Do not use ‘filter-list’ command.
Task 3
Check the results. R4’s LSDB and the routing table should not contain the two prefixes in question.
Lab Solution
Task 1
On R4, check the routing table. Make sure that it shows prefixes: 172.16.103.0/24 and 172.16.133.0/24.
Task 2
Configure router(s) so the 172.16.103.0/24 and 172.16.133.0/24 are not advertised to R4. Do not use ‘filter-list’ command.
R1 Configuration:
router-id 1.1.1.1
log-adjacency-changes
area 0 range 172.16.103.0 255.255.255.0 not-advertise
area 0 range 172.16.133.0 255.255.255.0 not-advertise
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
R2 Configuration
router-id 2.2.2.2
log-adjacency-changes
area 0 range 172.16.103.0 255.255.255.0 not-advertise
area 0 range 172.16.133.0 255.255.255.0 not-advertise
network 10.1.23.2 0.0.0.0 area 0
network 10.1.124.2 0.0.0.0 area 1
network 172.16.102.2 0.0.0.0 area 0
Task 3
Here, just a quick check of the routing table (LSDB checked but not shown here). Filtering has worked as expected.