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Mulicast groups and membership in the group

How can I view a members (ports) of multicast group on Cisco Catalyst 6500 switch? I can see all multicast groups, but I don't see a members of this groups. For example:

K#sh ip igmp membership 239.192.22.171

Flags: A - aggregate, T - tracked

L - Local, S - static, V - virtual, R - Reported through v3

I - v3lite, U - Urd, M - SSM (S,G) channel

1,2,3 - The version of IGMP, the group is in

Channel/Group-Flags:

/ - Filtering entry (Exclude mode (S,G), Include mode (G))

Reporter:

<mac-or-ip-address> - last reporter if group is not explicitly tracked

<n>/<m> - <n> reporter in include mode, <m> reporter in exclude

Channel/Group Reporter Uptime Exp. Flags Interface

*,239.192.22.171 x.x.x.x 00:31:13 02:21 2A Vl11

Can I see what ports are included in the multicast group?

1 ACCEPTED SOLUTION

Accepted Solutions
Cisco Employee

Re: Mulicast groups and membership in the group

Hi,

Multicast IP to MAC convertion is done by mapping Low-order 23 bits of Multicast IP address into low-order 23 bits of 0100.5e00.0000.

For example:

224.0.0.1 = 1110 0000.0000 0000.0000 0000.0000 0001 in binary

low order 23 bits = 000 0000.0000 0000.0000 0001

hex equivalent = 0 0 0 0 0 1

result of mapping = 0x0100.5e00.0001

http://www.cisco.com/en/US/tech/tk828/technologies_tech_note09186a0080094b55.shtml

HTH,

Nagendra

4 REPLIES
Silver

Re: Mulicast groups and membership in the group

hi!!!

The interface is seen in the command that you have specified as "Vl11" As vlan 11 is the L3 interface that you have it will figure as the interface for the igmp reports.

the traffic will be flooded on all the ports on that vlan unless igmp snooping is enabled.

If snooping is enabled you can check which ports in that vlan have recieved a igmp membership report. This is possible by looking in tha mac-address table for the multicast mac address.

eg :

sh mac-addresstable | i 0100

shows

999 0100.5e01.0101 static Yes - Gi4/1,Gi4/2,Router

which tells me that gi4/1 and 4/2 have recieved a membership report and added in the snooping table.

You can also use the command "sh ip igmp snooping stat" to know the L2 ports which are members of the multicast group.

Regards,

Niranjan

(please rate the post if it helps)

New Member

Re: Mulicast groups and membership in the group

Thank you! You have shown me the right direction. Command "sh mac-address-table multicast vlan 11 igmp-snooping" gives a list of ports, which are part of the multicats groups. For example:

11 0100.5e40.16ab static Yes - Te1/1

11 0100.5e40.0cd8 static Yes - Te1/1,Gi7/26,Gi7/27

But how do you know the MAC address of the group, knowing its IP address?

P.S. The command "sh ip igmp snooping stat" does not return any result.

Cisco Employee

Re: Mulicast groups and membership in the group

Hi,

Multicast IP to MAC convertion is done by mapping Low-order 23 bits of Multicast IP address into low-order 23 bits of 0100.5e00.0000.

For example:

224.0.0.1 = 1110 0000.0000 0000.0000 0000.0000 0001 in binary

low order 23 bits = 000 0000.0000 0000.0000 0001

hex equivalent = 0 0 0 0 0 1

result of mapping = 0x0100.5e00.0001

http://www.cisco.com/en/US/tech/tk828/technologies_tech_note09186a0080094b55.shtml

HTH,

Nagendra

New Member

Re: Mulicast groups and membership in the group

Thank you for exhaustive information! My "problem" was solved completely :)

BTW, one of the on-line "Multicast IP/MAC address converter" - http://ferlie.org/cgi-bin/multicast.cgi

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