[j-nsp] Problems with OSPF stub area (Juniper and Cisco)

Avram Dorfman avram@juniper.net
Fri, 8 Nov 2002 10:19:15 -0500

Hey Matti,

>> I suggest that you are better off having the routes. Can you add a
>> /32 from the range to a loopback somewhere? More importantly, why do
>> you need this route in OSPF if there are no destinations from it in
>> the area?
>      I'm sorry but I don't understand. There is a /25 which belongs to
>      that area and it doesn't show up in the forwarding table. That's
>      the problem I have. I'm sure it'll go away when somebody checks
>      the Ciscos configuration.

You're trying to get an ABR to "coalesce" (i.e. summarize, or 
aggregate, but coalesce is the OSPF RFC term) routes. In other words, 
you want to have multiple longer-mask routes in the range, in the stub area, but you only want to see the 
coalesced (or "aggregated") route outside the area.

Earlier in this thread, when I asked if the ABR actually /had/ any 
longer-mask routes in the range, you said it did not. We only coalesce 
routes if there are routes to coalesce. If there are no more specific 
OSPF routes in the area to coalesce, then there should be no need for 
the /25 route in OSPF either, so we don't generate it.

So, I asked why you need such a route to be in OSPF in the first place. 
If you do, I suggested that you should somehow ensure that there really 
is a more specific route from the range in the area. Otherwise, you 
should be looking at either exporting a route into OSPF, or perhaps you 
are also running BGP, and you could deal with this route there.

Sorry if my use of the word "coalesce" is confusing. People often call 
it summarizing, but that's not accurate when discussing OSPF, b/c it 
refers to generating type 3 and type 4 LSAs for other areas, which does 
not imply aggregation.