- Bronze, 100 points or more
My customer wants to see what multicast receivers are exist on IOS router segment by "show" command.
I investigated on IOS command reference but I couldn't find any command to do it.
Do you know any command to see it?
I think "show ip igmp groups" command displays "Last Reporter", but this indicates "Last host" not display all hosts receiving multicast stream and "show ip mroute" command displays (S, G) entries, but this indicates "source of multicast" not display "receivers of multicast".
your understanding is correct:
router takes care of Last reporter only for each group.
From the router point of view it is interested to know if there is at least one host interested in the group on the interface to put in Oilist.
By the way, even if the router could try to record all receivers its info would be incomplete for the IGMP report suppression feature used by IGMP v2.
A host suppresses its own report if heards another IGMP report message from another host for the same group G.
The only devices that can have an accurate picture are lan switches using IGMP snooping or older CGMP.
But you need to go to OSI L2 to find out what ports are currently associated to a multicast MAC address.
See this example from a C7609
sh mac-address-table multicast vlan 617 | beg 0100.5e48.6403
617 0100.5e48.6403 static Yes - Po1,Po277,Router
617 0100.5e48.6402 static Yes - Po1,Po277,Router
617 0100.5e48.6406 static Yes - Po1,Po277,Router
617 0100.5e00.0128 static Yes - Po1,Po277,Router
Here vlan617 is in a VRF, po1 is bundle to other C7609, po277 is internal bundle to FWSM (using a transparent context)
Note: things are different with IGMPv3
IGMPv3 has a feature called explicit-tracking and doesn't support report suppression (for the hosts joining (S,G) telling also the Source )
sh ip igmp snooping ?
>> explicit-tracking IGMPv3 Explicit tracking database
mrouter Show routers beyond a port
rate-limit IGMP messages incoming rate
statistics IGMPv3 channel statistics
So with IGMPv3 a router potentially could build a complete picture using this feature.
Hope to help