Chapter 14
| Multicast Filtering
Layer 2 IGMP (Snooping and Query for IPv4)
– 554 –
This attribute applies when the switch is serving as the querier (page 542), or as
a proxy host when IGMP snooping proxy reporting is enabled (page 542).
◆ Query Response Interval – The maximum time the system waits for a
response to general queries. (Range: 10-31740 tenths of a second in multiples
of 10; Default: 10 seconds)
This attribute applies when the switch is serving as the querier (page 542), or as
a proxy host when IGMP snooping proxy reporting is enabled (page 542).
◆ Last Member Query Interval – The interval to wait for a response to a group-
specific or group-and-source-specific query message. (Range: 1-31744 tenths
of a second in multiples of 10; Default: 1 second)
When a multicast host leaves a group, it sends an IGMP leave message. When
the leave message is received by the switch, it checks to see if this host is the
last to leave the group by sending out an IGMP group-specific or group-and-
source-specific query message, and starts a timer. If no reports are received
before the timer expires, the group record is deleted, and a report is sent to the
upstream multicast router.
A reduced value will result in reduced time to detect the loss of the last
member of a group or source, but may generate more burst traffic.
This attribute will take effect only if IGMP snooping proxy reporting is enabled
(page 542) or IGMP querier is enabled (page 542).
◆ Last Member Query Count – The number of IGMP proxy group-specific or
group-and-source-specific query messages that are sent out before the system
assumes there are no more local members. (Range: 1-255; Default: 2)
This attribute will take effect only if IGMP snooping proxy reporting or IGMP
querier is enabled.
◆ Proxy Query Address – A static source address for locally generated query and
report messages used by IGMP Proxy Reporting. (Range: Any valid IP unicast
address; Default: 0.0.0.0)
IGMP Snooping uses a null IP address of 0.0.0.0 for the source of IGMP query
messages which are proxied to downstream hosts to indicate that it is not the
elected querier, but is only proxying these messages as defined in RFC 4541.
The switch also uses a null address in IGMP reports sent to upstream ports.
Many hosts do not implement RFC 4541, and therefore do not understand
query messages with the source address of 0.0.0.0. These hosts will therefore
not reply to the queries, causing the multicast router to stop sending traffic to
them.
To resolve this problem, the source address in proxied IGMP query messages
can be replaced with any valid unicast address (other than the router’s own
address).
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