OSPF NBMA point-to-multipoint configuration

[duongla]

Hi all,

I connect 2 router using multipoint Framerelay connection and run ospf on both routers:

RTA s0/0 ---Frame Relay--- s0/0 RTB

1.1.1.1/24 1.1.1.2/24

For proper operation, I configure ospf network type point-to-multipoint on both serial interfaces. Everything is fine except one strange route in the routing table of each router:

RTA: sh ip ro

O 1.1.1.2/32 [110/64] via 1.1.1.2, 00:21:13, Serial0/0

RTB: sh ip ro

O 1.1.1.1/32 [110/64] via 1.1.1.1, 00:21:13, Serial0/0

Pls help me explain why ospf installs this kind of route and how to remove it from routing table (without using route filter )

Thanks

duongla

[Georg Pauwen]

Hello,

this is actually the default behaviour of OSPF point-to-multipoint networks.

´An OSPF point-to-multipoint interface is defined as a numbered point-to-point interface having one or more neighbors. It creates multiple host routes´.

Regards,

GP

[Richard Burts]

Georg is right that this is a normal behavior of OSPF. You can not and should not remove the /32 entries from the routing table. Part of how OSPF point to multipoint works is that it recognizes each of the neighbors that it might find on the multipoint connection and treats each neighbor separately (as if each neighbor were on a point to point) and forms adjacency with each neighbor. Having the unique entry in the routing table is part of how your router communicates with each neighbor.

HTH

Rick

[ruwhite]

Thos /32's are there so the remote sites can talk to each other, essentially, since the only way between the remotes is through the hub. It should be safe to filter these routes, or aggregate them, out of the hub towards the core of your network, but don't filter them between the remote sites (towards the remote sites).

HTH

:-)

Russ.W

[duongla]

Thanks all.

FYI, I have just found this useful link which is about ospf point-to-multipoint.

duongla

[duongla]

here is the link: http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a00801ec9ea.shtml

:)

duongla