All things related to multicast

[Toerless Eckert <>]

Philip,

YOu can ONLY keep effectively keep track of individual host memberships
when you are using IGMP version 3 because only IGMP version 3 does not
have the report suppression of IGMPv1/v2 that otherwise defies the
explicit tracking of hosts. 

If you have IGMP version 3 then you don't need switches, but you can
use the explicit tracking on the router side to see which host is
joined to which group or channel - see for example the feature description
of IGMPv3 explicit tracking in Cisco IOS 12.0(19)S documentation.

Yes, if you restrict yourselves to just one host per port then you
could get tracking of hosts also via an IGMP(v1/v2) snooping switch.
I am not aware of an explicit command to display this association though.
If you just have one host per port, you might as well get this information
out of matching the CAM table against the ARP and IGMP snooping table
(CAM: port -> host-mac, arp: host-mac -> host-ip, IGMP: groups -> portlist).
If you have more than one host per port you need IGMPv3 anyhow to really know
which subsets of hosts on a port is joined.

Cheers
        Toerless

On Wed, Apr 17, 2002 at 05:00:18PM +0800, Philip Ho 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
>