From: simon hart (simon.hart@btinternet.com)
Date: Tue Mar 29 2005 - 08:24:59 GMT-3
Hi Tim,
If that is the case then perhaps you can help out with the following.
The output here is from a router with no multicast enabled
Rack1R6#sh ip mroute
IP Multicast Routing Table
Flags: D - Dense, S - Sparse, B - Bidir Group, s - SSM Group, C - Connected,
L - Local, P - Pruned, R - RP-bit set, F - Register flag,
T - SPT-bit set, J - Join SPT, M - MSDP created entry,
X - Proxy Join Timer Running, A - Candidate for MSDP Advertisement,
U - URD, I - Received Source Specific Host Report, Z - Multicast
Tunnel
Y - Joined MDT-data group, y - Sending to MDT-data group
Outgoing interface flags: H - Hardware switched
Timers: Uptime/Expires
Interface state: Interface, Next-Hop or VCD, State/Mode
Hence no entries in the Mcast table.
Now if I ping and debug ip packet on this router I will get the following
output
Rack1R6#ping 239.9.9.9
Type escape sequence to abort.
Sending 1, 100-byte ICMP Echos to 239.9.9.9, timeout is 2 seconds:
.
Rack1R6#debug ip packet
IP packet debugging is on
Rack1R6#ping 239.9.9.9
Type escape sequence to abort.
Sending 1, 100-byte ICMP Echos to 239.9.9.9, timeout is 2 seconds:
*Mar 1 03:52:41.510: IP: s=54.1.4.6 (local), d=239.9.9.9 (Serial0/0), len
100, sending broad/multicast
*Mar 1 03:52:41.514: IP: s=141.1.36.6 (local), d=239.9.9.9
(FastEthernet1/0), len 100, sending broad/multicast
*Mar 1 03:52:41.514: IP: s=150.1.6.6 (local), d=239.9.9.9 (Loopback0), len
100, sending broad/multicast
*Mar 1 03:52:41.518: IP: s=150.1.6.6 (Loopback0), d=239.9.9.9, len 100,
unroutable.
I think that as you can see the packet has been sent out of each interface
that is currently 'up'.
Similarly, if I conduct a similar exercise from a multicast enabled router
the ping will go out of every interface, including the ones referenced
within the Mcast routing table.
Has me scratching my head a bit, but it must have something to do with a
ping not acting in the same way as a multicast stream. That is the the ping
is not trying to join a group as such. I think what is happening is that
the ping is sent out of every interface in the hope that it will hit a
router that has a tree entry for that group, that router would have to be
directly connected.
Simon
-----Original Message-----
From: ccie2be [mailto:ccie2be@nyc.rr.com]
Sent: 29 March 2005 12:17
To: 'simon hart'; 'Group Study'
Subject: RE: Pinging Multicast group
Simon,
Actually, I think that's not true.
The ping will only go out those interfaces listed in the OIL (Outgoing
Interface List0 which you can see by doing a show ip mroute.
Tim
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
simon hart
Sent: Tuesday, March 29, 2005 4:09 AM
To: Group Study
Subject: Pinging Multicast group
Hi all,
Can anyone enlighten me.
Whenever I ping a multicast group from a router, then the packet gets sent
out of all interfaces, even if an *,g or s,g exits for that group on the
router. Why does this behaviour occur?
Thanks
Simon
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