[Xorp-users] Well - I'm half working....

[Pavlin Radoslavov]

> Now, as I commented earlier, this cisco box has two routing
> engines installed.  The xorp's IP address to that connection to
> the cisco box is 144.124.34.30 as you can see from the above.
> The two routing engines have their own real IP addresses
> of 144.124.35.252 and 144.124.35.253.  But the idea is that one or
> other of them is supposed to adopt the address 144.124.34.254
> at any point in time.   All other machines get told that the
> default unicast router address is actually 144.124.34.254
> and one or other of the routing engines services that.
> 
> I wonder if the trouble is that although I've set the default
> mrib-route4 0.0.0.0/0 {
> >             metric: 1
> >             nexthop: 144.124.35.254
> >         }
> 
> the PIM neighbours actually get shown as 
> 
> Xorp> show pim neighbors  
> Interface    DRpriority NeighborAddr    V Mode   Holdtime Timeout
> rl3                none 144.124.35.252  2 Sparse      105      94
> rl3                none 144.124.35.253  2 Sparse      105      94
> Xorp> 
> 
> i.e. the two underlying IP addresses of the routing engines
> rather tha the common 144.124.35.254 that are supposed
> to service in a hot-standby type manner.

Yes, I think this is the problem. When the two engines originate PIM
Hello messages, they use source addresses 144.124.35.252 and
144.124.35.253 respectively. Hence, there is no PIM Hello message
with source address of 144.124.35.254 which is your default
next-hop router address. The easiest way to fix that is to modify
your default mrib-route4 entry and set the nexthop field to either
144.124.35.252 or 144.124.35.253.

> pavlin@icir.org said:
> > The reason that other sites are seeing your multicast beacon packets
> > is because your XORP multicast router is unicasting them encapsulated
> > within PIM Register packets. Those packets are sent directly to the
> > RP, and don't depend on any other multicast routers [see below].
> 
> I'm not sure.   If I run tcpdump on rl3 on the XORP box
> I see...
> 
> LiveCD# tcpdump -n -v -i rl3
> tcpdump: listening on rl3
> 10:53:47.884674 193.60.11.36.59810 > 233.3.18.1.56786: [udp sum ok] udp 51 (ttl 126, id 11069, len 79)
> 10:53:47.993499 193.60.11.36.59810 > 233.3.18.1.56786: [udp sum ok] udp 51 (ttl 126, id 11070, len 79)
> 10:53:48.103472 193.60.11.36.59810 > 233.3.18.1.56786: [udp sum ok] udp 51 (ttl 126, id 11071, len 79)
> 
> Surely those packets really are being sent out by multicast at that stage are
> they not?   Or am I misinterpreting the tcpdump output??

Your interpretation is correct. I didn't know that 144.124.35.252
and 144.124.35.253 belong to your upstream router, so now I have
another explanation why you were able to originate multicast
packets:
 * When the sender starts, the first few multicast data packets are
   encapsulated and unicast to the RP. By default, last-hop cisco
   routers will originate immediately (S,G) Joins toward the S once
   the first data packet is received.
 * Your XORP router will accept Join messages from your
   144.124.35.252/144.124.35.253 cisco router, hence it will start to
   forward the data packets natively.


Regards,
Pavlin