Multicast debugging

[Bill Nickless]

At 08:38 AM 7/12/99 -0700, Robert Olson wrote:
>At 08:31 AM 7/12/99 -0500, Linda Winkler wrote:
>>Unfortunately, mtrace on ciscos is broken.   known problem for a while.
>>no fix in site.
>
>Are there any alternate debugging tools?
>
>--bob

With session tools running, one looks at the routers to see if there are
mroutes in place.  On a Cisco, one runs

  show ip mroute 224.2.177.155

Which gives you a listing including entries like this

 destiny#show ip mroute 224.2.177.155
 IP Multicast Routing Table
 Flags: D - Dense, S - Sparse, C - Connected, L - Local, P - Pruned
        R - RP-bit set, F - Register flag, T - SPT-bit set, J - Join SPT
        X - Proxy Join Timer Running
 Timers: Uptime/Expires
 Interface state: Interface, Next-Hop or VCD, State/Mode 

 (*, 224.2.177.155), 3w4d/00:02:59, RP 130.202.192.1, flags: SJCF
   Incoming interface: ATM4/0, RPF nbr 130.202.128.1
   Outgoing interface list:
     ATM1/0.3, Forward/Sparse-Dense, 5d01h/00:02:14 

 (128.197.160.83, 224.2.177.155), 00:23:09/00:02:59, flags: CJT
   Incoming interface: ATM4/0, RPF nbr 130.202.128.1
   Outgoing interface list:
     ATM1/0.3, Forward/Sparse-Dense, 00:23:09/00:02:14

 (140.221.8.37, 224.2.177.155), 00:00:30/00:02:29, flags: CT
   Incoming interface: ATM1/0.3, RPF nbr 0.0.0.0
   Outgoing interface list:
     ATM4/0, 130.202.128.1, Forward/Sparse-Dense, 00:00:30/00:02:29

 [...many more records deleted]

This tells you that there is traffic on the 224.2.177.155 group (otherwise
there would be no reports at all) and that traffic is being heard from
128.197.160.83 and 140.221.8.37 at this router.

Note that there is no detectable difference between a broken network and
the lack of a multicast sender--both cases show up as no record in the
multicast router tables.  That's why it's so ipmortant to leave multicast
senders running during debugging.

When debugging multicast passing between Autonomous Systems, one runs Cisco
router commands like

   show ip mroute <group>
   show ip mbgp <etc>
   show ip msdp <etc>

Then one discusses the resulting output with the network management on the
other side of the link.  Configurations are tweaked, new router software is
installed, and routers are rebooted until the M-BGP and MSDP protocols are
working correctly.
--
Bill Nickless    http://www.mcs.anl.gov/people/nickless      +1 630 252 7390
PGP:0E 0F 16 80 C5 B1 69 52 E1 44 1A A5 0E 1B 74 F7     nickless at mcs.anl.gov