Brocade Communications Systems Brocate Ethernet Access Switch 6910 - Manual (Page 1120)

1070 Brocade 6910 Ethernet Access Switch Configuration Guide
53-1002581-01
Layer 2 IGMP (Snooping and Query)
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• 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 1059 )
or IGMP querier is enabled.
• 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).
Rules Used for Proxy Reporting
When IGMP Proxy Reporting is disabled, the switch will use a null IP address for the source of
IGMP query and report messages unless a proxy query address has been set.
When IGMP Proxy Reporting is enabled, the source address is based on the following criteria:
• If a proxy query address is configured, the switch will use that address as the source IP
address in general and group-specific query messages sent to downstream hosts, and in
report and leave messages sent upstream from the multicast router port.
• If a proxy query address is not configured, the switch will use the VLAN’s IP address as the
IP source address in general and group-specific query messages sent downstream, and
use the source address of the last IGMP message received from a downstream host in
report and leave messages sent upstream from the multicast router port.
Interface
To configure IGMP snooping on a VLAN:
1. Click Multicast, IGMP Snooping, Interface.
2. Select Configure VLAN from the Action list.