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3Com Switch 7750 Series
Command Reference Guide – Multicast Chapter 4 IGMP Configuration Commands
4-13
<3Com> system-view
System View: return to User View with Ctrl+Z.
[3Com] multicast routing-enable
[3Com] igmp report-aggregation
4.1.13 igmp robust-count
Syntax
igmp robust-count robust-value
undo igmp robust-count
View
VLAN interface view
Parameter
robust-value: IGMP robust value, number of sending the IGMP group-specific query
packets after the IGMP querier receives the IGMP Leave packet from the host. It is in
the range of 2 times to 5 times.
Description
Use the igmp robust-count command to set the number of sending the IGMP group
query message after the IGMP query router receives the IGMP Leave message from
the host.
Use the undo igmp robust-count command to restore the default value.
By default, an IGMP querier sends IGMP group-specific query packets twice.
In the shared network, that is, a same network segment including multiple hosts and
multicast routers, the query router is responsible for maintaining the IGMP group
membership on the interface. When the IGMP v2 host leaves a group, it sends an
IGMP Leave message. When receiving the IGMP Leave message, IGMP query router
must send the IGMP group-specific query message for specified times (by the
robust-value parameter in the igmp robust-count command, with default value as 2)
in a specified time interval (by the seconds parameter in the igmp
lastmember-queryinterval command, with default value as 1 second). If other hosts
which are interested in the specific group receive the IGMP group-specific query
packets from the IGMP query router, they will send back the IGMP Membership Report
packets within the specified maximum response time interval. If it receives the IGMP
Membership Report packets within the defined period (equal to robust-value ×
seconds), the IGMP query router continue to maintain the membership of this group.
When receiving no IGMP Membership Report packet from any hosts within the defined
period, the IGMP query router considers it as timeout and stops membership
maintenance for the group.