LevelOne GTL-2691 - Manual (Page 551)

C HAPTER 15 | Multicast Filtering
Layer 3 IGMP (Query used with Multicast Routing)
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the QRV field does not contain a declared robustness value, the switch
will set the robustness variable to the value statically configured by this
command. If the QRV exceeds 7, the maximum value of the QRV field,
the robustness value is set to zero, meaning that this device will not
advertise a QRV in any query messages it subsequently sends.
◆ Query Interval – Configures the frequency at which host query
messages are sent. (Range: 1-255; Default: 125 seconds)
Multicast routers send host query messages to determine the interfaces
that are connected to downstream hosts requesting a specific multicast
service. Only the designated multicast router for a subnet sends host
query messages, which are addressed to the multicast address
224.0.0.1, and use a time-to-live (TTL) value of 1.
For IGMP Version 1, the designated router is elected according to the
multicast routing protocol that runs on the LAN. But for IGMP Version 2
and 3, the designated querier is the lowest IP-addressed multicast
router on the subnet.
◆ Query Max Response Time – Configures the maximum response
time advertised in IGMP queries. (Range: 0-255 tenths of a second;
Default: 10 seconds)
IGMPv1 does not support a configurable maximum response time for
query messages. It is fixed at 10 seconds for IGMPv1.
By varying the Query Maximum Response Time, the burstiness of IGMP
messages passed on the subnet can be tuned; where larger values
make the traffic less bursty, as host responses are spread out over a
larger interval.
The number of seconds represented by the maximum response interval
must be less than the Query Interval.
◆ Last Member Query Interval – The frequency at which to send IGMP
group-specific or IGMPv3 group-source-specific query messages in
response to receiving a group-specific or group-source-specific leave
message. (Range: 1-255 tenths of a second; Default: 1 second)
When the switch receives an IGMPv2 or IGMPv3 leave message from a
host that wants to leave a multicast group, source or channel, it sends
a number of group-specific or group-source-specific query messages as
defined by the Last Member Query Count at intervals defined by the
Last Member Query Interval. If no response is received after this
period, the -switch stops forwarding for the group, source or channel.
◆ Querier – Device currently serving as the IGMP querier for this
multicast service. A querier can only be displayed if IGMP multicasting
is enabled, the VLAN for this entry is up, and is configured with a valid
IP address.