OSPF - Secondary address subnet is not being advertised?

[joch2joch]

Hi dear experts,

Need help! Please refer to the attached diagram

Currently, users in Branch Office (BO) access servers in HQ via the BO-A > HQ-A link. The servers are all located in the 10.10.20.0 subnet.

Our aim was to implement dynamic routing protocol to ensure high availability. But so far we have found that whenever the BO-A > HQ-A link fails, traffic doesn't route over to BO-B > HQ-B link...and we are forced to add a corresponding static route into router BO-A (ip route 10.10.20.0 255.255.255.0 BO-B)

When we run a 'show ip ospf database' for all the BO routers, we found that in BO-B and BO-C, the Type-5 AS External Link States section only has entries for the 10.10.10.0 subnet.

Is this problem due to the nature of secondary addresses? What is the resolution?

Thanks for the advice!!!

Joe

[Kevin Dorrell]

I am surprised that even the 10.10.10.0 subnet is appearing on a type-5. That suggests that it is being redistributed from a static or a connected rather than being seen directly by the OSPF on the HQ routers. If it were being seen by the OSPF directly, then it would be on a type-1 or a type-2 from the DR of that segment. (Assuming you are all one area.) Perhaps you could check whether OSPF is actually running on the Ethernet at HQ rather than just as a redistrubute connected.

Once you get OSPF running on the Ethernet at HQ, then both subnets should show up at BO.

There is something special about the secondary address, but I don't think it has anything to do with our problem here. Here it is anyway: OSPF can advertise the secondary address of a link quite happily, but it will not form adjacencies across the secondary subnet. But in your case the two HQ routers should be fine forming their adjacency across the 10.10.10.0/24 subnet provided OSPF is running on that interface.

Perhaps it would be useful to see the configs of the HQ routers, and show ip ospf neighbors.

Kevin Dorrell

Luxembourg

[joch2joch]

Hello Kevin,

Thanks for your feedback.

Indeed, the networks 10.10.10.0/24 and 10.10.20.0/24 are connected interfaces to HQ-A, as well as HQ-B.

I have new information to add;

When I issue a show ip ospf database on HQ-A and HQ-B, I don't even see the 10.10.20.0 network appearing... is this the reason BO-A, -B, and -C have not been receiving this network in the LSAs?

hmmmmmmm....

Thanks!

Joe

[Kevin Dorrell]

It sounds very much like you do not have OSPF running on the Ethernet at HQ. OSPF is only finding out about the 10.10.10.0 address because it is being redistributed from a static or a connected somewhere, which is why it is a type-5.

To get any further with this, I think we need to see the configs of the HQ router and see if there is a network statement covering the Ethernet.

Kevin Dorrell

Luxembourg

[alfredshum]

1) I cannot see BO-B in the diagram

2) In the diagram it said you've added a static route to 10.10.20.0/24 using HQ-A as next hop. But in your text you said you've added the same static route using BO-B as the next hop. So you got 2 static routes? Same AD?

3) If possible, let us know the configuration all of the routers.

[joch2joch]

Hi Alfred,

1)Do pardon my mistake...yes...my statement was contradicting my diagram. For simplicity, let's assume BO-B does not exist.

2)The static route via BO-C was only configured AFTER the BO-A > HQ-A link was down...because we realized the OSPF wasn't updating the routes :P

3)Sorry...actually, I don't really have access to the routers, and was hoping for some concept pointers.

Thanks mate!

Joe

[gaurav_saxena]

i hope you are using single area only. Adding network statement for subnets 10.10.10.0 & 10.10.20.0 under ospf config command should solve this problem.You can avoid to use redistribute connected.

[joch2joch]

Hello Gaurav,

Yes, we are using Area 0 for all routers :)

We have also added the necessary command as found in the recommendation in this Cisco document:

http://www.ciscotaccc.com/iprout/showcase?case=K16646601

However, we did configure the redistribute commands for the specified networks under the OSPF process

Thanks!

Joe

[alfredshum]

I think you don't even need any static routes and redistribution in your case. Remove them and try again.