point-to-multipoint OSPF not exchanging routes

[norteldude78]

I am bit confused here, but here it goes:

I have 3 routers connected to FR switch: R1 (hub), R2 and R3 (spokes)
2 PVCs: 1 between R1 and R2, the other between R1 and R3
Connectivity exists across each PVC.

The subnet I am using is 172.12.123.0/24
R1 is .1, R2 is .2, and R3 is .3

I have enabled ospf on the network 172.12.123.0 on each router.
Each router has a loopback, and I enabled ospf for that loopback (1.1.1.1, 2.2.2.2, and 3.3.3.3).

Neighbors were not forming automatically because this was an NBMA network.
On R1 serial interface I used the following command:
"ip ospf network point-to-multipoint"

Neighbors immediately formed (and I mean immediately!)

However routes were never exchanged...

When I changed R2 interface to multipoint, routes were finally exchanged between those two routers.

Can someone explain why the neighbors formed but the routes were never exchanged? The network types did not match, but neighbors were formed...

Also, if a hub is configured as ospf multipoint, do all the spokes have to be ospf multipoint?

Thanks,
-B

 

[norteldude78]

I think the problem may be with the NBMA requirements for a DR, and if one end is not acting like a DR, but the other end thinks it is the DR - I guess routes will not exchange. In this case R2 had thought that R1 was the DR, but R1 was ptmp so it didn't need a DR on the link...

Any other thoughts are appreciated....

 

[Minue]

Hello
The neighbors relationship formed because the timers for NBMA and point-to-multipoint.When you set R1 with the mention command,it started multicasting hello's.It only takes the hub to send hello's to spoke to form neighbors.
For the Routers to exchange routes they all have to be the same network types.
Regards