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Filtering External Type 1 routes between OSPF areas

Hello. I have a situation where I have two different telco's providing Metro Ethernet services to my site. Both providers will be sending me routes as OSPF external type 1's. I want to prevent the ISP's routers from peering with one another. One way I was thinking of accomplishing this is by making the connection to ISP1 under OSPF area 1 and to ISP2 area 2.

Is there a way I can filter the LSA's so no information is transferred between the two ISP routers in the two areas? Specifically, I don't want the type 5 LSA's generated by each ISP router to be sent to the other ISP router.


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Re: Filtering External Type 1 routes between OSPF areas


I do not think that configuring two areas will do what you need. But I think that you could achieve this by configuring separate OSPF processes. When you have separate processes they do not share information automatically. You must redistribute routes from one process to another and you can control what routes are redistributed.

Finding the optimum solution would require more knowledge of your environment and your complete requirements than we have. But I syspect that something like this will work for you:

configure ospf 1 and put the connection from ISP 1 into it. configure ospf 2 and put the connection from ISP 2 into it. configure ospf 99 (or whatever number you like) and put the connections from your network into that process. Then you can redistribute from 1 and 2 into 99 but not redistribute between 1 and 2. And if you need to advertise your routes to the ISPs then you probably need to redistribute from 99 into 1 and 2.



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