Digisol DG-FS4526E, Management Manual

Page: 531 / 1162

C
HAPTER
18 | Multicast Filtering
Layer 2 IGMP (Snooping and Query)
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This command applies when the switch is serving as the querier
( page 520 ), or as a proxy host when IGMP snooping proxy reporting is
enabled ( page 520 ).
Query Response Interval – The maximum time the system waits for
a response to proxy general queries. (Range: 10-31744 tenths of a
second; Default: 10 seconds)
This command applies when the switch is serving as the querier
( page 520 ), or as a proxy host when IGMP snooping proxy reporting is
enabled ( page 520 ).
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 (see page 520 ).
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).