Configuration Guide User guide

FastIron Configuration Guide 1463
53-1002494-02
IGMP snooping overview
MAC address. Groups having the same MAC address are switched to the same destination ports,
which are the superset of individual group output ports. Thus, the use of Layer 2 CAM might cause
unwanted packets to be sent to some ports. However, the switch generally needs far less Layer 2
CAM than it does Layer 4 CAM, which is required for each stream with a different source and group.
Queriers and non-queriers
An IGMP snooping-enabled Brocade device can be configured as a querier (active) or non-querier
(passive). An IGMP querier sends queries; a non-querier listens for IGMP queries and forwards
them to the entire VLAN. VLANs can be independently configured to be queriers or non-queriers. If
a VLAN has a connection to a PIM- or DVMRP-enabled port on another router, the VLAN must be
configured as a non-querier. When multiple IGMP snooping devices are connected together, and
there is no connection to a PIM- or DVMRP-enabled port, one of the devices must be configured as
a querier. If multiple devices are configured as queriers, after these devices exchange queries, then
all except the winner stop sending queries. The device with the lowest address becomes the
querier. Although the system will work when multiple devices are configured as queriers, Brocade
recommends that only one device (preferably the one with the traffic source) is configured as a
querier.
The non-queriers always forward multicast data traffic and IGMP messages to router ports which
receive IGMP queries or PIM or DVMRP hellos. Brocade recommends that you configure the device
with the data traffic source (server) as a querier. If a server is attached to a non-querier, the
non-querier always forwards traffic to the querier regardless of whether there are any clients on the
querier.
NOTE
In a topology of one or more connecting devices, at least one device must be running PIM or DVMRP
configured as active. Otherwise, none of the devices can send out queries, and traffic cannot be
forwarded to clients.
VLAN-specific configuration
IGMP snooping can be enabled on some VLANs or on all VLANs. Each VLAN can be independently
configured to be a querier or non-querier and can be configured for IGMP V2 or IGMP V3. In
general, the ip multicast commands apply globally to all VLANs except those configured with
VLAN-specific multicast commands. The VLAN-specific multicast commands supersede the global
ip multicast commands.
IGMP snooping can be configured for IGMP V2 or IGMP V3 on individual ports of a VLAN. An
interface or router sends the queries and reports that include its IGMP version specified on it. The
version configuration only applies to sending queries. The snooping device recognizes and
processes IGMP V2 and IGMP V3 packets regardless of the version configuration.
To avoid version deadlock, an interface retains its version configuration even when it receives a
report with a lower version.
Tracking and fast leave
Brocade devices support fast leave for IGMP V2, and tracking and fast leave for IGMP V3. Fast
leave stops the traffic immediately when the port receives a leave message. Tracking traces all
IGMP V3 clients. Refer to “Enabling IGMP V3 membership tracking and fast leave for the VLAN” on
page 1474 and “Enabling fast leave for IGMP V2” on page 1475.