weighted distributed static route in OSPF

[richmorrow624]

Is it possible to change the metric of a single static route, out of numerous routes being distributed (from a main site router)as a failover for the normally desired route?

The goal is to have the OSPF domain use the normal dynamic route learned from a remote site. Then, if that remote site goes down, have the OSPF domain use the distributed static route, which would direct the traffic through the main site.

Is this possible?

The main site router which would distribute this route is already distributing static subnets, so if this is possible, can you have numerous distribute statements also?

[Richard Burts]

Richard

I am not quite clear when you talk about distributing static routes whether you are talking about redistributing static routes into OSPF or whether you are talking about distributing in some other sense (like sending = advertising = distributing).

Assuming that you are talking about redistributing statics I believe that these points may be helpful:

- when you redistribute routes you can use a route map to control the redistribution. The route map can not only control which routes are redistributed but can control the metric of individual routes being redistributed. While I do not remember having done this in OSPF and therefore am not speaking from experience, it should work.

- I am not real clear why you want/need to alter the metric of the redistributed route - unless the same route was being redistributed on more than one router and you want some routes from one router to be preferred and some routes from the other router to be preferred. But I do not think that is what you are describing.

- OSPF has an order of preference for routes that over-rides the metric. OSPF will always prefer an intra-area route (an O route) over an inter-area route (an O IA route). And OSPF will always prefer an inter-area route over an external route (an O E) route.

- So if I am understanding your explanation you will have some remote site advertising some route(s) and you want all your OSPF routers to use the route advertised from the remote site. But if the remote site goes down there are static routes in the main site which are being redistributed into OSPF and you want all your OSPF routers to use the redistributed static routes. Assuming that the remote site is advertising its routes as intra-area or inter-area routes then your will get your desired behavior - without any need to manipulate the metric of the redistributed routes.

HTH

Rick

[richmorrow624]

Thanks for the reply,

The last two point are correct, this is the information I was looking for.

But, this brings up more questions:

If the remote site is advertising the route as the O or O IA route, what is the distributed route (as far as how the other remote sites see it)?

It has to be something less preferntial in order for the OSPF domain not to use it, until the remote site goes down.

[Richard Burts]

Richard

In OSPF a route originated by a network statement is an O route (intra-area) within its own OSPF area and is an O IA (inter-area) route within all other OSPF areas. Any route originated by redistribution is an External route (E1 or E2) within all OSPF areas.

The order of preference in OSPF is that:

O routes (intra-area) are most preferred

O IA routes (inter-area) are next preferred

O E routes (external) are least preferred.

So any route advertised via a network statement rather then by redistribution by the remote will always be more attractive to all the OSPF routers than any redistributed route. As long as the route advertised by the remote is in the routing table all the OSPF routers will use it. And if the remote stops advertising it then the redistributed static will go into the routing table and will be used.

I hope this is an adequate answer to your question.

HTH

Rick