Lab 31 - OSPF Default Routing

Prerequisites: CCNP level skills.

Note!

Use the configuration from Lab6.

Topology

Pic. 1 - OSPF Topology.

Icons designed by: Andrzej Szoblik - http://www.newo.pl

Task 1
Configure a default route on R1 pointing to s0/1 interface.

Task 2

Configure R1 so that it advertises the default route using OSPF and is preferred gateway to all unknown destinations. R2 should also advertise itself as the gateway unconditionally (even though it has not a default route in its routing table).

Lab Solution

Task 1

Configure a default route on R1 pointing to s0/1 interface.

R1 Configuration:

!

ip route 0.0.0.0 0.0.0.0 s0/1

!

Verification:

Pic. 2 - R1's Routing Table.

Task 2

Configure R1 so that it advertises the default route using OSPF and is preferred gateway to all unknown destinations. R2 should also advertise itself as the gateway unconditionally (even though it has not a default route in its routing table).

R1 OSPF Configuration:

!

router ospf 1
 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
 default-information originate

!

Verification:

Pic. 3 - R4's Routing Table.

Note!

R1 injects a default route with the metric=1.

R2 OSPF Configuration:

!

router ospf 1
 router-id 2.2.2.2
 log-adjacency-changes
 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
 default-information originate always metric 40

!

Note!
Since R2 does not have a default route in its routing table, it has to use the keyword 'always' to advertise it. R2 should not be a default gateway when R1 is available, its metric injected is larger than 1 (here: 40). However, R4's LSDB contains both of them but R1 is the preferred gateway based on the lower metric advertised.

Verification:

Pic. 4 - R4's Default Route from 1.1.1.1.

Pic. 5 - R4's Default Route from 2.2.2.2.