Chapter 14
| Multicast Filtering
Layer 3 IGMP (Query used with Multicast Routing)
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Configuring IGMP
Interface Parameters
Use the Multicast > IGMP > Interface page to configure interface settings for IGMP.
The switch uses IGMP (Internet Group Management Protocol) to query for any
attached hosts that want to receive a specific multicast service. The hosts may
respond with several types of IP multicast messages. Hosts respond to queries with
report messages that indicate which groups they want to join or the groups to
which they already belong. If a router does not receive a report message within a
specified period of time, it will prune that interface from the multicast tree. A host
can also submit a join message at any time without waiting for a query from the
router. Hosts can also signal when they no longer want to receive traffic for a
specific group by sending a leave-group message.
If more than one router on the LAN is performing IP multicasting, one of these is
elected as the “querier” and assumes the role of querying for group members. It
then propagates the service request up to any neighboring multicast router to
ensure that it will continue to receive the multicast service. The parameters
described in this section are used to control Layer 3 IGMP and query functions.
Note:
IGMP Protocol Status should be enabled on all the interfaces that need to
support downstream multicast hosts (as described in this section).
Note:
IGMP is disabled when multicast routing is disabled (see “Enabling Multicast
Routing Globally” on page 754).
Parameters
These parameters are displayed:
◆ VLAN – VLAN interface bound to a primary IP address. (Range: 1-4094)
◆ IGMP Protocol Status – Enables IGMP (including IGMP query functions) on a
VLAN interface. (Default: Disabled)
When a multicast routing protocol, such as PIM, is enabled, IGMP is also
enabled.
◆ IGMP Version – Configures the IGMP version used on an interface. (Options:
Version 1-3; Default: Version 2)
◆ Robustness Variable – Specifies the robustness (or expected packet loss) for
this interface. The robustness value is used in calculating the appropriate range
for other IGMP variables, such as the Group Membership Interval, as well as the
Other Querier Present Interval, and the Startup Query Count (RFC 2236).
(Range: 1-255; Default: 2)
Routers adopt the robustness value from the most recently received query. If
the querier's robustness variable (QRV) is zero, indicating that the QRV field
does not contain a declared robustness value, the switch will set the robustness
variable to the value statically configured by this command. If the QRV exceeds
7, the maximum value of the QRV field, the robustness value is set to zero,
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