All things related to multicast

[Philip Ho <>]

ken lindahl wrote:

> >I believe you need to look on the router (which is doing IGMP) that is
> >speaking to the switch with CGMP.
>
> i don't think the router maintains enough state. i can't see
> any cgmp state at all; as far as i know, when the router sees a
> join/leave, it sends the corresponding cgmp message and then
> forgets about it. "show ip igmp group" shows only the most
> recent responder to membership queries, one member per interface.
> one could probably turn on debugging and log the messages, but
> that seems inelegant.
>

Agree. To be exact, I would say, "only one receiver IP could be recorded per
leaf interface per group." This is one of the phenomenon of high scalability
of IP multicast. Right?

>
> if the network is all switched, all cisco, one could probably
> deduce the L2 forwarding tree from "sh cgmp" on the switches,
> the find the MAC addresses of the clients attached to the "leaf"
> ports, then go to the router and find the ip addrs from the arp
> table... but that seems inelegant.
>
> ken
>

>From "sh cgmp" output, MAC address of the clients are NOT recorded. (at least
in my 2900XL) Hence each client IP address could not be found.

Regards,
philip


>
> At 10:09 AM 4/17/2002 -0400, Alan Crosswell wrote:
> >> Dear all
> >>
> >> Does anyone know how to retrieve multicast receiver IP attaching to
> >> Cisco layer-2 switches 2900XL and 3550? I could only get group MAC
> >> address together with outgoing interface(s) using "sh cgmp" command. (I
> >> know that I could grep it using debug cgmp but is there another
> >> solution?) Thanks a lot!
> >>
> >> The sample "sh cgmp" output is as follows:
> >>
> >> c2900#sh cgmp
> >> CGMP is running.
> >> CGMP Fast Leave is running.
> >> Default router timeout is 300 sec.
> >>
> >>
> >> vLAN     IGMP MAC Address   Interfaces
> >> ------  -----------------   -----------
> >>     1    0100.5e00.0128      Fa0/1
> >>     1    0100.5e05.0647      Fa0/1 Fa0/4
> >>
> >>
> >> vLAN     IGMP Router        Expire   Interface
> >> ------  -----------------  --------  ----------
> >>     1    0001.4294.cda1     251 sec   Fa0/1
> >>
> >>
> >> Regards,
> >> philip
> >> Hong Kong IP Multicast Initiative (HKIPMI)
> >> Department of Information Engineering
> >> The Chinese University of Hong Kong
> >> Phone : 2603 5240
> >> Fax : 2603 5032
> >>
> >
> >I believe you need to look on the router (which is doing IGMP) that is
> >speaking to the switch with CGMP.
> >/a