Allied Telesis AR400 manual Multiple host mode for fast leave

IGMP fast leave > Explanation of IGMP fast leave

Multiple host mode for fast leave

The previous discussion assumes that only one client is attached to the port on the Snooper. Imagine instead a situation where multiple clients are attached to a single port on the snooping switch, as the following figure shows.

Multicast Server:
TV source for
channels 1-3
port 1
AT-8948	Switch 1:
	Querier
port 49
		port 26	Rapier 24i
				Switch 3:
			port 3	Snooper
	TV A	TV B	TV C	TV D
Channel:	1	2	3	3
				igmp-snooper.eps

In this situation, you need to use fast leave in multiple host mode. In multiple host mode, the Snooper tracks which clients are joined to a given IP multicast group on a given port. The Snooper shuts off the multicast group to that port as soon as the last client leaves the group on the port.

Multiple host mode is available in Software Version 291-08 and later.

The alternative mode is called single host mode. In single host mode, as soon as the Snooper receives a leave message for a group on a port, it shuts off the multicast. This mode assumes that there are no other clients on the port that are still interested in receiving the multicast, so is suitable only when clients are directly attached to the Snooper.

To specify multiple mode, use the command:

set igmpsnooping vlan={name1..4094all} fastleave=multiple

To specify single mode, use either of the commands:

set igmpsnooping vlan={name1..4094all} fastleave=single set igmpsnooping vlan={name1..4094all} fastleave=on

Page 67 AlliedWare™ OS How To Note: IGMP