Install guide

IP Multicasting 25
detects a change, it generates a special IGMP Leave message known as a Query
Solicit, and floods the Query Solicit message to all ports. When the IGMP
Querier receives the message, it responds by sending a General Query. This
refreshes snooped group membership information in the network.
Query solicitation functions by default (without you enabling it) on the root
bridge in an STP topology. By default, the root bridge always sends a Query
Solicit message when the topology changes.
In other switches in the network, the query solicitation is disabled by default,
but you can enable it by using the command:
set igmpsnooping vlan={vlan-name|1..4094|all}
querysolicit={on|yes|true}
If you enable query solicitation on a switch other than the STP root bridge, both
that switch and the root bridge send a Query Solicit message.
Once the Querier receives the Query Solicit message, it sends out a General
Query and waits for responses, which update the snooping information
throughout the network. If necessary, you can reduce the time this takes by
tuning the IGMP timers, especially the queryresponseinterval parameter. For
more information, see the “IGMP Timers and Counters” section of “How To
Configure IGMP on Allied Telesyn Routers and Switches for Multicasting”.
This How To Note is available in the Resource Center of the Documentation
and Tools CDROM for Software Version 2.8.1, or from
www.alliedtelesis.co.uk/en-gb/solutions/techdocs.asp?area=howto
On any switch, you can disable query solicitation by using the command:
set igmpsnooping vlan={vlan-name|1..4094|all}
querysolicit={off|no|false}
To see whether query solicitation is on or off, check the Query Solicitation field
in output of the show igmpsnooping command on page 86.
Blocking All-Groups Entries
IGMP snooping all-groups allows you to prevent a port or ports from acting as
an all-groups entry.
Sometimes the device cannot differentiate between certain multicast addresses
and permanent host groups at Layer 2. For example, this happens with the
addresses 239.0.0.2 and 224.0.0.2 where 224.0.0.2 is the all-routers multicast
group. If the device receives an IGMP report for the 239.0.0.2 address, which
has a MAC address of 01-00-5e-00-00-02, the device creates an all-groups entry
in the MARL. All further multicast groups are added to this port, so multicast
traffic is forwarded out the port.
By preventing a port or ports from receiving an all-groups entry, you can limit
the number of router ports on the device, and therefore the volume of multicast
traffic sent over the device’s ports. Once disabled with the disable ip igmp
allgroup command, the port no longer creates MARL entries when the device
receives an IGMP report, query, or multicast data over any other port. For
example, if port 9 has been disabled as an all-groups port, an all-groups entry
will be created for port 9. This will happen when the port receives packets that
will create an IGMP router port, such as reserved multicast groups and IGMP
queries. However, a subsequent IGMP report received over port 7 will have an