OSPF, Multiple default routes

[avilt]

I have the OSPF network setup as attached. OSPF is running ony on routers and L3 switch. I would like to inject 2 default routes into the Layer 3 switch.

Both routers C and D gets the default route as expected. But the L3 switch inserts default route as Router C only.

I would like to see 2 default routes on the switch as both the links have same cost. How can I troubleshoot this?

The command "SHOW IP OSPF DATABASE" shows the following output on the L3 switch.

Type-5 AS External Link States

Link ID ADV Router Age Seq# Checksum Tag

0.0.0.0 10.0.0.9 701 0x8000E7D4 0x5D24 65182

0.0.0.0 10.0.0.54 442 0x8000E7EB 0x4EEA 65182

But the show ip route command on the L3 switch shows only one default route.

Thank You

[avilt]

Thank You for the valuable inputs.

So I will enable passive interface on both the routers towards the firewall. I should also disable the ospf command "network 10.0.0.0 255.0.0.0 area0/1" right?

Thank You very much

[Harold Ritter · Accepted solution]

Avil,

If you remove the network statement then you do not need to configure the interface as passive. Either way should work.

Can you do a show ip ospf border on L3-Switch to see if both ASBRs (Rtr-A and Rtr-B) are considered as equal cost.

Let me know if this solves your problem,

[avilt]

Entered "passive interface" command on RTRB(Area1), now the L3Switch takes default route via RTRB. I will try the same command on RTRA later. Anyway thank you very much for the help.

[Harold Ritter]

Avil,

Have you tried the show ip ospf border command just to make sure that both ASBRs are considered equal by L3-switch.

Regards,

[avilt]

Yes, the cost is same to reach RTRA & RTRB.

L3SWITCH#show ip ospf border-routers

OSPF Process 65182 internal Routing Table

Codes: i - Intra-area route, I - Inter-area route

I 10.0.0.9 [2] via 172.16.0.9, Port-channel10.20, ASBR, Area 0, SPF 37

i 172.16.0.54 [1] via 172.16.0.54, Port-channel10.20, ASBR, Area 0, SPF 37

i 10.0.0.54 [2] via 172.16.0.54, Port-channel10.20, ASBR, Area 0, SPF 37

i 172.16.0.9 [1] via 172.16.0.9 , Port-channel10.20, ABR, Area 0, SPF 37

[Harold Ritter]

Wonderful. The passive interface trick should definitely solve the issue then.

Regards,