OSPF, Frame Relay and /32

ilya.varlashkin · ‎03-15-2007

Hi,

consider following small frame relay network:

[r1]

| Se0

|

/ \

DLCI 102 / \ DLCI 103

[r2] [r3]

Configuration of frame relay is done entierly on main serial interface on all routers (i.e. sub-interfaces are not used). All interfaces are in the same /24 subnet. OSPF is configured on these interfaces as point-to-multipoint (alternatively as 'broadcast'). Once adjacency is formed, spoke routers will install /32 routes for each other spoke via hub router. All works fine, each spoke can ping other spoke without a problem.

For many years I just took for granted that such setup works, because it just seems to be natural to install /32 in order to get connectivity between spokes. But today I started to wonder where such behaviour is specified. I went through several RFC, digged in Cisco and Juniper documentation but couldn't find anything on the topic.

Does anyone know some document, which specifies/formalises installation of /32 routes in scenarios where two routers are on the same subnet but not OSPF neighbors? Is this universal behaviour or have somebody experienced different with other manufacturers?

ruwhite · ‎03-16-2007

This isn't documented anyplace that I know of.... I poked through the RFC, and it's not there, that I can find. In fact, I don't think point-to-multipoint is documented at all.

In general, this is universal behavior. I know Cisco, Juniper, Redback, and all the other vendors I've checked do this. You'll note that these implementations were all done by a small number of folks who actually all know each other, so the implementations are very similar, in the way they act, even in areas outside the official RFCs.

HTH

:-)

Russ