The purpose of a group membership query is to discover the multicast groups to which
a host belongs.
IGMPv2 and IGMPv3 group membership queries have a Max Response Time field. This
response time is the maximum amount of time that a host can take to reply to a query.
Group Membership Reports
When a host receives a group membership query, it identifies the groups associated with
the query and determines to which groups the query belongs. The host then sets a timer,
with a value less than the Max Response Time field in the query, for each group to which
it belongs.
When the timer expires, the host sends a group membership report to the group address.
When a multicast router receives a report, it adds the group to the membership list for
the network and sets a timer to the group membership interval. The router calculates the
group membership interval using the following formula of configurable IGMP values:
( query interval x robustness value ) + query maximum response time
If this timer interval expires before the router receives another group membership report,
the router determines that the group has no members left on the network.
IGMPv3 supports an extended report format you can use to report multiple groups and
source lists in a single report.
Leave Group Membership Messages
When a host leaves a group, it sends a leave group membership message to multicast
routers on the network. A host generally addresses leave group membership messages
to the all-routers group address (224.0.0.2).
Platform Considerations
For information about modules that support IGMP on the ERX7xx models, ERX14xx
models, and the ERX310 Broadband Services Router:
•
See ERX Module Guide, Table 1, Module Combinations for detailed module specifications.
•
See ERX Module Guide, Appendix A, Module Protocol Support for information about the
modules that support IGMP.
For information about modules that support IGMP on the E120 and E320 Broadband
Services Routers:
•
See E120 and E320 Module Guide, Table 1, Modules and IOAs for detailed module
specifications.
•
See E120 and E320 Module Guide, Appendix A, IOA Protocol Support for information
about the modules that support IGMP.
43Copyright © 2010, Juniper Networks, Inc.
Chapter 2: Configuring IGMP
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