Multiple queriers. Here is a little CLI guide on how to setup IGMP snooping:

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1 Here is a little CLI guide on how to setup IGMP snooping: IGMP snooping is usually done per VLAN and thus I will focus on that. You always need at least one querier, per VLAN, in your IGMP snooping setup and you need to ensure IGMP snooping is done on all switches. The role of the querier is to query and distribute IGMP join/leave updates to the switches in the topology. The querier is needed in order for switches to populate their MFDB (Multicast Forwarding Database Table). Even if you only have one switch, then that switch must be setup for both IGMP snooping and IGMP querier. Config - You will enable IGMP snooping per VLAN - VLANs where IGMP snooping is not enabled will simply flood multicast, as usual - I am doing snooping for VLAN 10 in this example - Setup snooping for VLAN 10 - I want SW1 to be the querier for VLAN 10 (SW1) (Vlan)#set igmp 10 (SW1) (Vlan)#set igmp querier 10 (SW1) (Vlan)#set igmp querier 10 address Setup snooping for VLAN 10 - I don t need IGMP querier here, as SW1 is the querier for VLAN 10. (SW2) >enable (SW2) #vlan database (SW2) (Vlan)#set igmp 10 (SW2) (Vlan)#end Multiple queriers You can set multiple switches to be querier. However, only one querier per VLAN, should be active at any one time. If you are configuring multiple queriers in the same VLAN, then the other querier(s) should act as a failover system. The way it works is by the querier IP addresses. These querier IP addresses can be anything you want really. It is not an actual IP address. It is used as part of an election process. The querier with the lowest IP address value, will be the elected querier for that VLAN.

2 You need to enable Querier Election Participate Mode. This is not enabled per default. Generally, all queriers in the VLAN should patriciate in the election mode. To enable Querier Election Participate Mode, is again done from the VLAN database. The below commands will enable it for VLAN 10. (SW1) (Vlan)#set igmp querier election participate 10 In my setup, if I want SW1 to be the main querier for VLAN 10 and SW2 to be the secondary querier for VLAN 10, I would do as follows (full config incl. enabling snooping): (SW1) (Vlan)#set igmp 10 (SW1) (Vlan)#set igmp querier 10 (SW1) (Vlan)#set igmp querier 10 address (SW1) (Vlan)#set igmp querier election participate 10 (SW2) >enable (SW2) #vlan database (SW2) (Vlan)#set igmp 10 (SW2) (Vlan)#set igmp querier 10 (SW2) (Vlan)#set igmp querier 10 address (SW2) (Vlan)#set igmp querier election participate 10 (SW2) (Vlan)#end

3 Here is a CLI guide on how to setup Multicast routing. IGMP routing is used in scenarios where multicast must traverse between networks (i.e. between VLANs). Per design, the default behaviour of multicast is that it will always stays within the same Network/VLAN. To allow multicast across networks, we need to implement IGMP routing. There are 3 forms of multicast routing supported on the Netgear switches: PIM-DM, PIM-SM and DVMRP. I will focus on PIM-DM in this guide. NOTE: You can use IGMP snooping together with IGMP routing. They are two different things! IGMP snooping does mcast filtering on layer 2 (within a VLAN) and IGMP routing forwards mcast on Layer 3 (between networks). NOTES: If you are routing multicast, then be careful about the TTL (Time To Live) on packets. Typically, multicast packets have a low TTL value and that can cause the packet to no get routed across the entire network. If you need packets to be routed across one routing hop (as in scenario no. 1, below), then the multicast packets needs a TTL value of at least 2. Same way, if you need packets to be routed across two routing hops (as in scenario no. 2, below), then the multicast packets needs a TTL value of at least 3, and so on. The TTL is always set by the source device. If you need a higher TTL, due to the amount of routing hops the packet needs to travel through, then adjust the source software (sending the mcast traffic) to up the TTL value. PIM-DM Protocol Independent Multicast - Dense Mode (PIM-DM) is an mcast routing protocol used for situations where you have a simple network topology, with 1-2 routing hops. I have made two setups below. One demonstrating how PIM-DM would work when there is one L3 device doing all the routing and another scenario showing the same principle, but with two L3 routing devices. Config no. 1 - Two VLANs on the switch: VLAN 10 and VLAN 20 - Inter-VLAN routing done from the switch - Any multicast traffic must be routed between VLAN 10 and VLAN 20 - The setup of inter-vlan routing, routing interfaces, etc. is not shown in the below config. Only the mcast part is shown. It is assumed that the VLAN routing is setup and working SW config (L3-SW1) >enable (L3-SW1) #configure (L3-SW1) (Config)#ip multicast (L3-SW1) (Config)#ip igmp (L3-SW1) (Config)#ip pim dense (L3-SW1) (Config)# interface vlan 10 (L3-SW1) (Interface vlan 10)#ip igmp

4 (L3-SW1) (Interface vlan 10)#ip pim (L3-SW1) (Interface vlan 10)#exit (L3-SW1) (Config)# interface vlan 20 (L3-SW1) (Interface vlan 20)#ip igmp (L3-SW1) (Interface vlan 20)#ip pim (L3-SW1) (Interface vlan 20)#end That is it! Config no. 2 - Two switches with two VLANs on each switch - Routing VLAN 99 between the switches - Any multicast traffic must be routed between all VLANs - The setup of inter-vlan routing, routing interfaces, etc. is not shown in the below config. Only the mcast part is shown. It is assumed that the VLAN routing is setup and working (L3-SW1) >enable (L3-SW1) #configure (L3-SW1) (Config)#ip multicast (L3-SW1) (Config)#ip igmp (L3-SW1) (Config)#ip pim dense (L3-SW1) (Config)# interface vlan 10 (L3-SW1) (Interface vlan 10)#ip igmp (L3-SW1) (Interface vlan 10)#ip pim (L3-SW1) (Interface vlan 10)#exit (L3-SW1) (Config)# interface vlan 20 (L3-SW1) (Interface vlan 20)#ip igmp (L3-SW1) (Interface vlan 20)#ip pim (L3-SW1) (Interface vlan 20)#exit (L3-SW1) (Config)# interface vlan 99 (L3-SW1) (Interface vlan 99)#ip igmp (L3-SW1) (Interface vlan 99)#ip pim (L3-SW1) (Interface vlan 99)#end (L3-SW2) >enable (L3- SW2) #configure

5 (L3- SW2) (Config)#ip multicast (L3- SW2) (Config)#ip igmp (L3- SW2) (Config)#ip pim dense (L3- SW2) (Config)# interface vlan 30 (L3- SW2) (Interface vlan 30)#ip igmp (L3- SW2) (Interface vlan 30)#ip pim (L3- SW2) (Interface vlan 30)#exit (L3- SW2) (Config)# interface vlan 40 (L3- SW2) (Interface vlan 40)#ip igmp (L3- SW2) (Interface vlan 40)#ip pim (L3- SW2) (Interface vlan 40)#exit (L3- SW2) (Config)# interface vlan 99 (L3- SW2) (Interface vlan 99)#ip igmp (L3- SW2) (Interface vlan 99)#ip pim (L3- SW2) (Interface vlan 99)#end