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 R3, check the routing table. Make sure that it shows prefixes: 172.16.104.0/24 and 172.16.144.0/24.
Task 2
Configure router(s) so R3 does not receive 172.16.104.0/24 and 172.16.144.0/24 prefixes.
Task 3
Check the results.
Lab Solution
Task 1
On R3, check the routing table. Make sure that it shows prefixes: 172.16.104.0/24 and 172.16.144.0/24.
Task 2
Configure router(s) so R3 does not receive 172.16.104.0/24 and 172.16.144.0/24 prefixes.
Note!
R1 Configuration:
ip prefix-list DENY_R4_LOOPBACKS seq 10 deny 172.16.144.0/24
ip prefix-list DENY_R4_LOOPBACKS seq 15 permit 0.0.0.0/0 le 32
!
router-id 1.1.1.1
log-adjacency-changes
area 1 filter-list prefix DENY_R4_LOOPBACKS out
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:
ip prefix-list DENY_R4_LOOPBACKS seq 10 deny 172.16.144.0/24
ip prefix-list DENY_R4_LOOPBACKS seq 15 permit 0.0.0.0/0 le 32
!
router-id 1.1.1.1
log-adjacency-changes
area 1 filter-list prefix DENY_R4_LOOPBACKS out
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
Task 3
Check the results.
