10-21-2004 02:45 AM - edited 03-02-2019 07:26 PM
I have a router (cat3750) in an OSPF normal area that is not an ABR/ASBR.
This router has multiple stub networks directly connected to it,
all having IPs 10.10.x.0/24. The router will source one LSA 1 for
each stub /24 network connected. However, with the IP numbering
scheme used in the OSPF domain it is desirable that this router
would be able to source an aggregate 10.10.0.0 /16 into the area.
The problem is that I do not want to convert this router into ASBR
(or nssa-asbr) and source the summary as LSA 5 (or 7).
I wonder if there might be a way to trick the router into sending
an aggregated LSA 1 for all of its directly connected stub networks.
Any suggestions would be welcomed.
10-21-2004 05:39 AM
Unfortunately, it is not possible to do that unless you generate a type 5 LSA from that router.
The way to generate a summary stub network within the type 1 LSA would be to assign the aggreagte address to a loopback interface for instance and to have this address define under the ospf process. But IOS will not allow you do have overlapping addresses.
So the only way I can think of is to create a summary static route (ip route 10.10.0.0 255.255.0.0 null0) and redistribute it in ospf.
Hope this helps,
10-21-2004 08:50 AM
Thank you Harold.
The interesting question which arises is: Why cisco IOS does not permit overlapping addressing on Loopback?
Within the routing paradigm "More specific route first" I would not see any problem with doing that.
E.g., 10.10.10.0 /24 connected
10.10.11.0 /24 connected
10.10.0.1 /16 Loopback
all packets arriving on that router with destinations 10.10.10.x, 10.10.11.x will be sent
to connected nets; all other within 10.10.0.0/16 --
to Loopback (which will act as a drop bucket).
alex
10-21-2004 10:35 AM
Alex,
I totally agree with you that conceptually this would not hurt. This flexibility has probably never been requested. Would probably be useful in this kind of scenario. You could still do the aggregation using a type 5 LSA.
Hope this helps,
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