1

What adverse effects could occurred if I set the igmp snooping querier query-interval to 1 second in the switch?

The default in switch is 60 seconds

0

Decreasing the query interval could needlessly increase the traffic on your LAN segment.

IGMP is between a host and a router, not a switch. A switch can snoop on IGMP, but it doesn't do IGMP queries.

8
  • Is it mean the IGMP snooping is different from IGMP querying?
    – Hendrik
    Nov 23 '15 at 9:08
  • IGMP queries are between a router and the hosts. The switch would normally be ignorant of IGMP, but IGMP snooping allows the switch to snoop on the queries so that it can send multicasts to only those switch ports which have hosts actually listening for those multicasts. Normally, a switch would flood multicasts to all ports.
    – Ron Maupin
    Nov 23 '15 at 9:14
  • Thanks for your reply @ron. I still have not understand it clearly, So without a router, is a host could get the multicast traffic send from the multicast source? I'm currently facing issue for the implementation of IPTV. When a host (in my case is android setopbox with igmp support) just recently boot up, the host couldn't play the IPTV channel. It must wait for around 2 minutes to play the channel. After that, if I stop and start again the channel, it's instantly play. I'm trying to shorten the query interval, but afraid of disturb the currently running switch in my network.
    – Hendrik
    Nov 23 '15 at 9:27
  • There is something else going on. The host will send an IGMP request when the application starts. A router would receive the request and forward multicasts out the router port, and it will query out that port every query interval to see if there are still hosts interested in receiving the multicast. If both the server and client are on the same layer-2 switch, in the same VLAN, I don't think IGMP plays a role in your problem. More likely the server is buffering for two minutes before it starts sending.
    – Ron Maupin
    Nov 23 '15 at 9:36
  • I think it's in the same VLAN, so it's pointless to set the IGMP Snooping querier query interval in the switch? I haven't further investigate the work of server in sending multicast traffic to network, but I think the server is always broadcast the channel to network. When I check ethstats of the server, its showing total: 0.00 Mb/s In 69.58 Mb/s Out - 0.9 p/s In 6405.4 p/s Out I need assistance to fix that behaviour, do I need to open another question? :D
    – Hendrik
    Nov 23 '15 at 9:53
1

The default, per spec is 125 seconds.

Set to 1 (one) second would result in a broadcast storm as every multicast capable device answers the query.

3
  • I believe the query interval is 125 seconds on NX-OS, but it is 60 seconds on IOS.
    – Ron Maupin
    Nov 23 '15 at 9:05
  • Checking the IOS router at hand, 120s. The 2960S's default to 125.
    – Ricky
    Nov 23 '15 at 22:00
  • OK, obviously the real router wins. I looked at this IP Multicast Commands for IOS 12.2, and this Configuring IGMP for NX-OS.
    – Ron Maupin
    Nov 23 '15 at 22:05

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