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We've enabled IGMP snooping on one of our VLANs. The configuration used is:

bridge multicast filtering
ip igmp snooping
ip igmp snooping vlan 1
ip igmp snooping vlan 1 querier

We're now seeing the message "%BRG_IGMP_QRR-W-DUPLICATE_IP: Duplicate IGMP Querier IP address 192.168.142.1 detected on VLAN 1. Remote MAC address is 34:a8:4e:0d:34:55."

The IP address and MAC address belong to this switch... so I'm puzzled as to why the switch is identifying itself as a duplicate IGMP Querier IP.

Am I totally misunderstanding what this message means? It looks like it's logged every time a multicast packet is sent from one of our stock system applications, which uses the multicast address 239.255.0.1.

We're using Cisco SG300-28P switches, running v1.4.1.3 firmware. This particular switch is in layer 3 mode and has multiple VLAN interfaces.

  • I've seen "big cisco" have those issues as well, if there's any sort of loop in the network. (i.e. something repeating the igmp query) – Ricky Beam Oct 7 '15 at 7:02
  • Hi Ricky. RSTP is enabled on all switches on the network. I've used Wireshark to see if there's anything odd going on, but apart from these spurious messages that the switch is generating, I can't see anything that suggests there's a loop in the network. I'm wondering now if the issue is purely because the switch is in router mode and there's something different I need to do with the configuration... or perhaps I should move IGMP querier onto a switch that's in layer 2 mode? – Matty Brown Oct 7 '15 at 7:18
  • It doesn't have to be a full-on loop. Anything that echos the query will cause it. (lots of things have various bits of multicast brain damage) – Ricky Beam Oct 7 '15 at 7:54
  • When monitoring with Wireshark, I actually see two IGMP general queries from the IGMP querier address. The two packets have different identifiers - so they're not the same packet bouncing around and hitting the same host twice... either something is, as @RickyBeam says echoing the query, or the switch really is sending out two queries, which can only be a bug in the firmware. – Matty Brown Oct 7 '15 at 19:36
  • I made our firewall the IGMP router. I'm no longer seeing duplicate IGMP general membership queries. I think the issue is with a bad firmware for this switch. I'll have to ask the guy at Cisco that's dealing with my support case to check this in their lab and see if they have the same issue on the firmware I'm running (latest). – Matty Brown Oct 7 '15 at 20:51

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