Lab 20 - OSPF Path Influencing Using Cost

Prerequisites: CCNP level skills.

Topology

Pic. 1 - OSPF Topology.

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

Task 1

On R1 check the paths towards 10.1.23.0/24.

Task 2
Manipulate the OSPF cost so R1 prefers R2 towards 10.1.23.0/24.


Lab Solution

Task 1

On R1 check the paths towards 10.1.23.0/24.

Note!

Changing the cost on Loopback interfaces does not influence the path selection. R2 is the DR (representative) providing access to what is advertised by the originator of the subnets 172.16.102.0/24 and 172.16.103.0/24. There is only ONE originator of these subnets unlike 10.1.23.0/24.

Pic. 2 - R1 Routing Table.

Task 2

Manipulate the OSPF cost so R1 prefers R2 towards 10.1.23.0/24.

Note!
Both R2's and R3 's cost towards 10.1.23.0/24 is 1 (auto-cost reference-bandwidth = 100,000,000/bandwidth of the F1/0 interface). R1's cost of s0/0 = 64.

Pic. 3 - R2's Cost to 10.1.23.0/24.

Pic. 4 - R3 Cost to 10.1.23.0/24.

R3 Configuration:

!

interface FastEthernet1/0
 ip address 10.1.23.3 255.255.255.0
 ip ospf cost 2
!

Verification:

Pic. 5 - R1's Routing Table