Configuration Guide User guide

1634 FastIron Configuration Guide
53-1002494-02
MLD snooping overview
MLD Snooping requires hardware resources. If the device has insufficient resources, the data
stream without a resource is mirrored to the CPU in addition to being VLAN flooded, which can
cause high CPU usage. To avoid this situation, Brocade recommends that you avoid enabling
snooping globally unless necessary.
When any port of a VLAN is configured for MLDv2, the VLAN matches both source and group (S G)
in hardware switching. If no port is configured for MLDv2, the VLAN matches group only (* G).
Matching (S G) requires more hardware resources than (* G) when there are multiple servers
sharing the same group. For example, two data streams from different sources to the same group
require two (S G) entries in MLDv2, compared to only one (* G) in MLDv1. Brocade recommends
that you use MLDv2 only in a source-specific application. Because each VLAN can be configured for
the version independently, some VLANs might match (* G) while others match (S G).
To receive data traffic, MLD Snooping requires clients to send membership reports. If a client does
not send reports, you must configure a static group to force traffic to client ports. The static group
can either apply to some ports or to the entire VLAN.
Configuring queriers and non-queriers on
MLD snooping-enabled devices
An MLD Snooping-enabled device can be configured as a querier (active) or non-querier (passive).
An MLD querier sends queries; a non-querier listens for MLD queries and forwards them to the
entire VLAN. VLANs can be independently configured as queriers or non-queriers. If a VLAN has a
connection to an IPv6 PIM-enabled port on another router, the VLAN should be configured as a
non-querier. When multiple MLD snooping devices are connected together, and there is no
connection to an IPv6 PIM-enabled port, one of the devices should be configured as a querier. If
multiple devices are configured as queriers, after multiple devices exchange queries, then all
devices except the winner (the device with the lowest address) stop sending queries. Although the
system works when multiple devices are configured as queriers, Brocade recommends that only
one device, preferably the one with the traffic source, is configured as the querier.
Because non-queriers always forward multicast data traffic and MLD messages to router ports
which receive MLD queries or IPv6 PIM hellos, Brocade recommends that you configure the devices
with the data traffic source (server) as queriers. If a server is attached to a non-querier, the
non-querier always forwards traffic to the querier regardless of whether or not there are clients on
the querier.
NOTE
In a topology with one or more connected devices, at least one device must be running PIM, or
configured as active. Otherwise, no devices can send queries, and traffic cannot be forwarded to
clients.
MLD snooping configuration on VLANs
You can configure MLD snooping on some VLANs or all VLANs. Each VLAN can be independently
enabled or disabled for MLD snooping, or can be configured with MLDv1 or MLDv2. In general, the
ipv6 mld-snooping... commands apply globally to all VLANs except those configured with
VLAN-specific mld-snooping... commands. VLAN-specific mld-snooping commands supersede
global ipv6 mld-snooping commands.