Mutlicast question

[rmv72]

i have next

2610#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, s - SSM

Outgoing interface flags: H - Hardware switched

Timers: Uptime/Expires

Interface state: Interface, Next-Hop or VCD, State/Mode

(*, 239.255.255.250), 00:02:58/00:02:59, RP 0.0.0.0, flags: D

Incoming interface: Null, RPF nbr 0.0.0.0

Outgoing interface list:

Serial0/0.2, Forward/Dense, 00:02:58/00:00:00

(10.10.0.118, 239.255.255.250), 00:02:58/00:00:01, flags: PT

Incoming interface: Serial0/0.2, RPF nbr 192.168.100.2

Outgoing interface list: Null

(*, 224.0.1.40), 06:43:07/00:00:00, RP 0.0.0.0, flags: DCL

Incoming interface: Null, RPF nbr 0.0.0.0

Outgoing interface list:

Ethernet0/0, Forward/Dense, 06:43:07/00:00:00

Serial0/0.2, Forward/Dense, 06:41:14/00:00:00

2610#sh ip igmp groups

IGMP Connected Group Membership

Group Address Interface Uptime Expires Last Reporter

224.0.1.40 Ethernet0/0 06:43:53 00:02:58 1xx.xxxx.xxx.1

From #sh ip mroute output i see 2 multicast groups,but from #sh ip igmp groups output only one. Why it's so?

[donewald · Accepted solution]

The igmp group cmd shows only groups that the router is joined.

224.0.1.40 is a reserved group for the Auto- P's to use so they will join this to share group information.

Here's a link on the 224.0.1.40 group's purpose:

http://www.cisco.com/en/US/partner/tech/tk828/tk363/technologies_white_paper09186a00800d6b63.shtml

The show mroute will show all S,G (Source Group) route information the router has within it's Multicast routing table. This does not need to match your igmp joins.

Hope this helps you,

Don