From: Matt Bentley (mattdbentley@gmail.com)
Date: Tue Apr 15 2008 - 11:17:35 ART
Hi GS:
I understand the theory behind multicast and WHY things don't work, but it
seems like the KEY to be ablle to fix a MCAST problem is to be able to look
at the "debug ip mpacket" output, the MCAST routing table, understand what's
going on, and then take appropriate action. Could someone help me to
understand exactly how to decode the mcast routing table? I know that the
entry with 224.0.1.39 is the RP and the 224.0.1.40 is the Mapping agent, but
am having difficulty finding parallels any further than that. Any help
would be greatly appreciated. I have included the Mcsat Table from one of
my switches. Thanks very much in advance.
THREE#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, z - MDT-data group sender,
Y - Joined MDT-data group, y - Sending to MDT-data group
Outgoing interface flags: H - Hardware switched, A - Assert winner
Timers: Uptime/Expires
Interface state: Interface, Next-Hop or VCD, State/Mode
(*, 225.0.0.1), 00:22:48/stopped, RP 15.15.15.15, flags: SJCLF
Incoming interface: FastEthernet0/3, RPF nbr 3.3.3.1
Outgoing interface list:
FastEthernet0/2, Forward/Sparse, 00:19:41/00:03:16, H
(2.2.2.2, 225.0.0.1), 00:00:06/00:02:53, flags: LFT
Incoming interface: FastEthernet0/1, RPF nbr 0.0.0.0, Registering
Outgoing interface list:
FastEthernet0/2, Forward/Sparse, 00:00:06/00:02:53, H
(3.3.3.2, 225.0.0.1), 00:00:07/00:02:52, flags: LFT
Incoming interface: FastEthernet0/3, RPF nbr 0.0.0.0
Outgoing interface list:
FastEthernet0/2, Forward/Sparse, 00:00:07/00:02:52, H
(8.8.8.1, 225.0.0.1), 00:00:07/00:03:22, flags: PLT
Incoming interface: FastEthernet0/2, RPF nbr 0.0.0.0
Outgoing interface list: Null
(13.13.13.13, 225.0.0.1), 00:00:08/00:03:21, flags: LFT
Incoming interface: Loopback0, RPF nbr 0.0.0.0, Registering
Outgoing interface list:
FastEthernet0/2, Forward/Sparse, 00:00:08/00:02:51
(*, 224.0.1.39), 2w2d/stopped, RP 0.0.0.0, flags: DC
Incoming interface: Null, RPF nbr 0.0.0.0
Outgoing interface list:
FastEthernet0/1, Forward/Sparse, 2w2d/00:02:19
(15.15.15.15, 224.0.1.39), 2w2d/00:02:51, flags: T
Incoming interface: FastEthernet0/3, RPF nbr 3.3.3.1
Outgoing interface list:
FastEthernet0/1, Forward/Sparse, 2w2d/00:02:19
(*, 224.0.1.40), 2w2d/stopped, RP 0.0.0.0, flags: DCL
Incoming interface: Null, RPF nbr 0.0.0.0
Outgoing interface list:
FastEthernet0/1, Forward/Sparse, 2w2d/00:02:14
(12.12.12.12, 224.0.1.40), 2w2d/00:02:31, flags: PLTX
Incoming interface: FastEthernet0/1, RPF nbr 2.2.2.1
Outgoing interface list: Null
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