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Community Member

IP multicast is backfed to sources

Interfaces on the same VLAN receive IP multicast's from other streamers on the same VLAN. This doesn't scale well and it is not a proper setup for each streamer to automatically receive one another's multicast.

Problem description detail:

Streamer 1 and 2 are both apart of vlan 967. Streamer 2 receives all multicast streams from streamer 1 without any requests. Conversely, streamer 1 receives all of streamer 2's multicasts! I need to prevent the streamers traffic from hitting one another.

Global:

no ip igmp snooping

ip multicast-routing

Source VLAN with backfeed problem:

interface Vlan967

description Modulus Encoders

ip address 10.1xx.yy.65 255.255.255.0

ip pim sparse-dense-mode (same result with just ip pim)

end

sho ip mrout count | i 239.20.0.2

Group: 239.1.7.2, Source count: 1, Packets forwarded: 1847630873, Packets received: 1847630873

If I remove PIM from the source vlan then the 6500 does not seem to recognize the multicast coming in from the streamers. The mroute doesn't show up but the traffic counters in the Ethernet interface continue to increment:

interface Vlan967

description Modulus Encoders

ip address 10.1xx.yy.65 255.255.255.0

end

sho ip mrout count | i 239.1.7.2

Group: 239.1.7.2, Source count: 0, Packets forwarded: 0, Packets received: 0

It would make sense to have IGMP snooping on for the streamer vlan but the Cisco does not seem to accept the command (after issuing the command it does not show up in the vlan interface configuration).

Other info about the network that is a requirement and working fine with the current setup:

Most of my interfaces require me to send the multicast's without any igmp requests. This is easy to do with the ip igmp static-group command such as in this destination VLAN:

interface Vlan973

description Spare-C7-Network

ip address 10.1xx.zz.65 255.255.255.0

ip pim dense-mode

ip igmp static-group 239.20.0.12

ip igmp static-group 239.10.0.66

ip igmp static-group 239.50.0.78

ip igmp static-group 239.70.3.0

ip igmp static-group 225.73.73.1

ip igmp static-group 226.73.73.2

ip igmp static-group 226.73.73.3

ip igmp static-group 226.73.73.4

Of course I also have periodic testing that requires me to make an IGMP request from another vlan and request multicast streams from the source vlan 967. For instance, if I'm plugged in as a client to a port apart of vlan 943 I can make an IGMP request and pull the multicast from 967 no prob.

3 REPLIES
Hall of Fame Super Blue

Re: IP multicast is backfed to sources

Hi

If you have disabled IGMP snooping then the switch will have to flood the multicast traffic to all ports. Which switch type is it ?

If you do a "sh ip igmp membership

Jon

Community Member

Re: IP multicast is backfed to sources

6509 SUP720 MSFCv3 running IOS 12.2(18)SXD4

Client (10.239.173.251) VLAN configuration:

interface Vlan943

ip address 10.1x.yy.1 255.255.255.0

ip helper-address 10.xxx.yyy.zzz

ip pim dense-mode

end

With PIM enabled on the source vlan (967)

Channel/Group Reporter Uptime Exp. Flags Interface

*,239.1.7.2 0.0.0.0 00:26:33 stop 2SA Vl943

*,239.1.7.2 10.239.173.251 00:27:18 02:20 2A Vl947

*,239.1.7.2 0.0.0.0 03:42:21 stop 2SA Vl973

With PIM removed from vlan 967 the igmp membership is empty.

Thanks for the assistance Jon!

Hall of Fame Super Blue

Re: IP multicast is backfed to sources

PIM being enabled on the interface is what sends out the IGMP queries. Without it there will be no igmp queries and so no igmp responses.

if you only needed to have multicast on vlan 967 then you can turn off PIM on the interface and enable the "igmp snooping querier" function on the 6500. The IGMP querier function then sends out IGMP queries.

Something has to query for members to report.

That explains your PIM/no PIM issue.

However it looks like you want to access that group from other vlans so you do need PIM on the interface.

But you also need IGMP snooping or else it will flood to all ports as said before.

I need to lab something up so i'll get back to you.

Jon

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