Interpreting OSPF routes.

[jitenshah18]

Just one small question regarding OSPF routes in the Cisco routing tables : These are the routes from a routing table.

O       130.126.0.20/30

           [110/20] via 130.126.0.86, 3d12h, TenGigabitEthernet1/1

           [110/20] via 130.126.0.17, 3d12h, TenGigabitEthernet6/3

O  IA    192.17.20.0 [110/112] via 192.17.17.41, 3d12h, Vlan3420

O  E2    72.36.117.248/30 [110/0] via 172.19.89.41, 3d12h, Vlan3220

I do not have a detailed understanding of OSPF protocol but had just few questions .

1. the IA (Inter-Area) and E2 (External type 2) are summarization routes ?

2. Can IA and E2  have multiple entries for same destination as something similar to the highlighted entry ?

like for e.g. the E2 route  72.36.117.248/30 can have 2 possible outgoing ports ? (I feel no if they are summarization routes but if someone could help me confirming.)

[Richard Burts]

1) the routes advertised in IA and in E2 may be summarized routes but they may also be not summarized routes. It is the default behavior and is more common for IA and E2 to be not summarized routes.

2) IA and E2 can easily have 2 outgoing ports similar to the highlighted entries in your post. Having two ports like that is an indication that OSPF has learned 2 equivalent routes to the same destination and will support equal cost load sharing.

HTH

Rick

[jitenshah18]

thank you Rick.

[jitenshah18]

O IA      130.126.0.20/30

           [110/20] via 130.126.0.86, 3d12h, TenGigabitEthernet1/1

           [110/20] via 130.126.0.17, 3d12h, TenGigabitEthernet6/3

O E2  130.126.0.20/30

           [110/20] via 130.126.0.86, 3d12h, TenGigabitEthernet1/1

           [110/20] via 130.126.0.17, 3d12h, TenGigabitEthernet6/3

Do these entries look like these ?

thanks.

[Richard Burts]

Yes they would look like that.

HTH

Rick