Allied Telesis AR400 manual Speeding up IGMP convergence in a non-looped topology

Query solicitation (rapid recovery from topology changes) > Speeding up IGMP convergence in a non-looped topology

Speeding up IGMP convergence in a non-looped topology

The previous section described how it can take up to 125 seconds for multicasting to recover in a non-looped topology after a port comes back up. You can speed up convergence simply by enabling RSTP. This enables the network to use Query Solicitation and means that multicasting resumes within 3 seconds of the link coming up.

Even though there is no loop in the network, one of the switches becomes the STP root bridge—it does not matter which switch does this. When the link comes up, the root bridge detects the topology change and sends a Query Solicitation.

So you just need to enter the following commands on all switches:

enable stp=default

set stp=default mode=rapid

Enabling query solicitation on multiple switches in a looped topology

On networks that use spanning tree or EPSR, Query Solicitation is not normally required on switches other than the STP root bridge or EPSR master node. Therefore, it is only enabled by default on the root bridge and the master node.

However, in some networks you may need to turn on Query Solicitation on all switches—for example, if the network includes other switches that do not support Query Solicitation and therefore the STP root bridge may be a switch that does not send Query Solicit messages. To enable Query Solicitation, use the command:

set igmpsnooping vlan={vlan-name1..4094all} querysolicit={on yestrue}

Every switch that has Query Solicitation enabled sends a Query Solicit message when it detects a topology change. Enabling it on multiple switches means you get multiple messages, but has no other disadvantage.

The following figure shows a the packet flow for a four-switch network with Query Solicitation enabled on all the switches.

Page 33 AlliedWare™ OS How To Note: IGMP