[Xorp-users] Re: help establishing OSPF adjacencies

[Nick Feamster]

On Mon, Oct 17, 2005 at 05:22:21PM -0700, Atanu Ghosh wrote:
> ---------------------------------------- RFC 2328
> 	Broadcast networks
> 	    Networks supporting many (more than two) attached routers,
> 	    together with the capability to address a single physical
> 	    message to all of the attached routers (broadcast).
> 	    Neighboring routers are discovered dynamically on these nets
> 	    using OSPF's Hello Protocol.  The Hello Protocol itself
> 	    takes advantage of the broadcast capability.  The OSPF
> 	    protocol makes further use of multicast capabilities, if
> 	    they exist.  Each pair of routers on a broadcast network is
> 	    assumed to be able to communicate directly. An ethernet is
> 	    an example of a broadcast network.
> ----------------------------------------

Why not just use ethernet as the broadcast medium, then?


> Then the routers are not seeing each others packets.


Yep.  I suspect that the routers are not joining the multicast group
properly.  tcpdump shows :

12:58:16.282879 IP planetlab4.csail.mit.edu > OSPF-ALL.MCAST.NET:
OSPFv2, Hello (1), length: 44

and

12:55:03.896093 IP planetlab5.csail.mit.edu > OSPF-ALL.MCAST.NET:
OSPFv2, Hello (1), length: 44

but, for some reason, they aren't hearing each other's hellos.  I
suspect it's a problem with multicast.  I see the attemt to join the
multicast group in the XORP debug:

[ 1068  +430 xrl_io.cc join_multicast_group ] Join Interface eth0 Vif
eth0 mcast 224.0.0.5

But I suspect that it is not succeeding for some reason.

-Nick

> 
>     >> After I saw you original message I went back and checked that
>     >> adjancencies are still being formed and they are.
>     >> 
>     >> I found one thing a little puzzling the checksum for both routers
>     >> for different LSAs is the same, is this the actual output?
> 
>     Nick> No, I had a copy/paste error.  The checksums are different.
> 
> Good - thats what I guessed:-).
> 
>      Atanu.