Dell S4048T, Configuration Manual

Page: 433 / 1277

Adjusting Timers
The following sections describe viewing and adjusting timers.
To view the current value of all IGMP timers, use the following command.
• View the current value of all IGMP timers.
EXEC Privilege mode
show ip igmp interface
For more information, refer to the example shown in Viewing IGMP Enabled Interfaces .
Adjusting Query and Response Timers
The querier periodically sends a general query to discover which multicast groups are active. A group must
have at least one host to be active.
When a host receives a query, it does not respond immediately, but rather starts a delay timer. The delay time
is set to a random value between 0 and the maximum response time. The host sends a response when the
timer expires; in version 2, if another host responds before the timer expires, the timer is nullified, and no
response is sent.
The maximum response time is the amount of time that the querier waits for a response to a query before
taking further action. The querier advertises this value in the query (refer to the illustration in
IGMP Version 2 ).
Lowering this value decreases leave latency but increases response burstiness because all host membership
reports must be sent before the maximum response time expires. Inversely, increasing this value decreases
burstiness at the expense of leave latency.
When the querier receives a leave message from a host, it sends a group-specific query to the subnet. If no
response is received, it sends another. The amount of time that the querier waits to receive a response to the
initial query before sending a second one is the last member query interval (LMQI). The switch waits one
LMQI after the second query before removing the group from the state table.
• Adjust the period between queries.
INTERFACE mode
ip igmp query-interval
• Adjust the maximum response time.
INTERFACE mode
ip igmp query-max-resp-time
• Adjust the last member query interval.
INTERFACE mode
ip igmp last-member-query-interval
Internet Group Management Protocol (IGMP) 433