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Configuring the Switch
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• Last Member Query Interval – A multicast client sends an IGMP leave message
when it leaves a group. The router then checks to see if this was the last host in
the group by sending an IGMP query and starting a timer based on this command.
If no reports are received before the timer expires, the group is deleted.
(Range: 0-25 seconds; Default: 1 second)
- This value may be tuned to modify the leave latency of the network. A reduced
value results in reduced time to detect the loss of the last member of a group.
• Max Query Response Time – Configures the maximum response time advertised
in IGMP queries. (Range: 0-25 seconds; Default: 10 seconds)
- The switch must be using IGMPv2 for this command to take effect.
- This command defines how long any responder (i.e., client or router) still in the
group has to respond to a query message before the router deletes the group.
- By varying the Maximum Query Response Time, you can tune the burstiness of
IGMP messages passed on the subnet; 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.
• 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.
- 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, the designated
querier is the lowest IP-addressed multicast router on the subnet.
• Robustness Variable – Specifies the robustness (i.e., expected packet loss) for
this interface. The robustness value is used in calculating the appropriate range for
other IGMP variables, such as the Group Membership Interval
(
Last Member
Query Interval
)
, as well as the Other Querier Present Interval, and the Startup
Query Count (RFC 2236). (Range: 1-255; Default: 2)
• Version – Configures the IGMP version used on an interface.
(Options: Version 1 or 2; Default: Version 2)
- All routers on the subnet must support the same version. However, the multicast
hosts on the subnet may support either IGMP version 1 or 2.
- The switch must be set to version 2 to enable the Max Query Response Time.
• Querier – Device currently serving as the IGMP querier for this multicast service.