igmp snooping not working? multicast flooding...

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luiswu
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Joined: 07 Apr 2015
Posts: 13

PostPosted: Thu May 07, 2015 23:18    Post subject: igmp snooping not working? multicast flooding... Reply with quote
Hi,

I am using a v24-sp2 K3 ARM 25648 build which has a igmp snooping option available under Setup > Networking for the br0 bridge.

I have an IPTV decoder connected to the bridge as well as other computers in the same subnet, when I realized that my build allowed igmp snooping I enabled it to prevent the multicast traffic directed to the IPTV decoder from flooding all the LAN.

However, much to my surprise after activating this option I can see with tcpdump that the UDP multicast traffic is reaching the other computers in the LAN, just as if the igmp snooping was turned off.

I've also realized that the /sys/devices/virtual/net/br0/bridge/multicast_snooping file contains a zero value, but it doesn't help either if I echo a "1" into the file.

My question is: is there any other build where the igmp snooping is working or are there any other actions that have to be taken in order to activate it?

PS. I am aware that I can isolate the IPTV decoder into its own vlan in order to prevent the traffic from reaching other computers, but I would like have all the equipments in the same subnet given that the snooping functionality seems to be available.
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Per Yngve Berg
DD-WRT Guru


Joined: 13 Aug 2013
Posts: 1101

PostPosted: Sat May 09, 2015 7:51    Post subject: Reply with quote
http://www.dd-wrt.com/wiki/index.php/Setting_up_IPTV_without_impact_to_LAN_and_Wireless_traffic

http://www.dd-wrt.com/phpBB2/viewtopic.php?t=264294
luiswu
DD-WRT Novice


Joined: 07 Apr 2015
Posts: 13

PostPosted: Sat May 09, 2015 15:13    Post subject: Reply with quote
Thanks for the info

I already did that and yes, I can isolate the IPTV traffic into one subnet and prevent the rest of the lan from being flooded (or block the traffic to other subnets/lans, for that matter).

My intention was though to make use of the igmp snooping functionality to have all the devices in the same subnet and the igmp snooper keeping track of the port to which the IPTV decoder is attached by means of igmp control messages. In that case the snooper sends the multicast traffic only to that port, preventing the lan from being flooded.

This is a standard functionality in many stock firmwares and it looked like it was also available in the latests DD-WRT builds (I believe it is incorporated in the kernel), but I can't get it to work.

Has anybody succeeded in making the igmp snooping functionality work?
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