Lessons learned about UDP multicast performance
Posted: September 25th, 2009 | Author: Joakim Andersson | Filed under: internet | 2 Comments »If you want to use UDP multicast to distribute data between nodes in a network from for example your Java program it is important to notice that unless you have a Layer 2 switch with support for IGMP snooping the data will be sent to all ports on the switch. This will naturally affect the performance of the multicast stream and also the available bandwidth on the network.
A Layer 2 switch with support for IGMP snooping will do the expected, which is to only send the multicast data sent to a multicast group to the ports which have joined the same multicast group.
IGMP snooping is a process whereby a Layer-2 switch passively listens (or “snoops”) the Layer-3 IGMP traffic to determine which ports are interested in receiving certain multicast traffic. The switch listens for IGMP Query, Report and Leave protocol messages. If desired, IGMP snooping can be configured on a per-VLAN basis. Traffic will be dynamically forwarded only to those ports that want to receive the multicast transmission. This can significantly reduce the amount of multicast traffic passing through a Layer-2 network, thus better utilizing the available bandwidth.
If you see poor performance in your UDP multicast tests, take a look at your switch. You might find the reason right there.
Worst, if you dont setup IGMP on heavy traffics the all network could be down ! I work in an ipTV company and we have a lot of HD contant streamed over the network and without IGMP forget :)
That’s very true!
Unfortunately it doesn’t seem like many switches that normal people have support it, one actually has to make an effort and find a higher-end switch with explicit support for IGMP snooping. That’s what happened for us, we thought we have decent switches in the office but naturally they did not support IGMP snooping.