OSPF redistribution

[Andreas Martensson]

Our organization has a specific site managing internet connection and all other ospf areas in the network reach it by a default route propagated from the site. On my site i have a couple of branch offices connected throug E1 serial connections. When a serial interface goes down the hit in the router table is the default route. This is giving some problems at the internet managenent site. Is there a way to advertise the serial interface so that my local router drops the package before sending it to default route. Mayby like "redistribute connected always (even if if down)" or something?

/Andreas

[Harold Ritter]

you could configure a static summary route covering all of you internal addresses and point this route to null0. This way when the serial interface goes down, traffic destined for the remote site would hit this summary route, be dropped locally and would therefore not affect your Internet management site. Under normal conditions, the more specific route would be used.

As an example, if you use RFC1918 internally for your network, such as 10.0.0.0/8, just configure ip route 10.0.0.0 255.0.0.0 null0.

Hope this helps,

[Andreas Martensson]

Thanx for your reply.

Does it matter if the route to the E1 network shows up as IA or E2 at my site? Does my campus router drop paket from IA routes and forward E2 to default route since the area is different?

I am not sure that i can use summary default route. There isn't a simple way to summarize the nets.

[Harold Ritter]

It doesn't matter what you inject the default route as. If you loose the route to your remote site, the packets will follow the default route to your Internet gateway.

Note that another approach could be to use the "classful" behavior, where if you already have an entry in the RIB under one majornet, packet forwarding for another destination belonging to the same majornet has to be resolved within the scope of that majornet. The default route would therefore not be used in this case. I don't know if that would help in your case since I don't know enough about your addressing plan.

To use classful behavior, you just need to configure "no ip classless".

Hope this helps,