Quick Reference Guide

442 PowerConnect B-Series TI24X Configuration Guide
53-1002269-02
PIM SM traffic snooping overview
18
• A user can configure static router ports to force all multicast traffic to these specific ports.
• Fast leave for IGMPv2 is supported. Fast leave stops traffic immediately when the port receives
a leave message.
• Tracking and fast leave for IGMPv3 is supported. If the only client on a port leaves, traffic is
stopped immediately.
• An IGMP device can be configured as a querier (active) or non-querier (passive). Queriers send
queries. Non-queriers listen for queries and forward them to the entire VLAN.
• Every VLAN can be independently configured to be a querier or a non-querier.
• If a VLAN has a connection to a PIM-enabled port on another router, this VLAN should be
configured as a non-querier (passive). When multiple snooping devices connect together and
there is no connection to PIM ports, one device should be configured as a querier (active). If
multiple devices are configured as active (queriers), only one will keep sending queries after
exchanging queries.
• An IGMP device can be configured to rate-limit the forwarding IGMPv2 membership reports to
queriers.
• The querier must configure an IP address to send out queries.
The implementation allows snooping on some VLANs or all VLANs. Each VLAN can independently
enable or disable IGMP, or configure V2 or V3. In general, global configuration commands ip
multicast apply to every VLAN except those that have local multicast configurations (which
supersede the global configuration). IGMP also allows independent configuration of individual
ports in a VLAN for either IGMPv2 or IGMPv3. Configuring a specific version on a port or a VLAN
only applies to the queries sent by the device. The device always processes client reports of any
version regardless of the configured version.
IGMP snooping requires hardware resources. If resources are inadequate, the data stream without
a resource is mirrored to CPU in addition to being VLAN flooded, which can cause high CPU usage.
Dell recommends that you avoid global enabling of snooping unless necessary.
When any port in a VLAN is configured for IGMPv3, the VLAN matches both source and group (S G)
in hardware switching. If no ports are configured for IGMPv3, the VLAN matches group only (* G).
Matching (S G) requires more hardware resources than matching (* 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 IGMPv3, but only one (* G) in IGMPv2. To conserve resources,
IGMPv3 should be used only in source-specific applications. When VLANs are be independently
configured for versions, some VLANs can match (* G) while others match (S G).
IGMP snooping requires clients to send membership reports in order to receive data traffic. If a
client application does not send reports, you must configure static groups to force traffic to client
ports. A static group can apply to only some ports or to the entire VLAN.
PIM SM traffic snooping overview
When multiple PIM sparse routers connect through a snooping-enabled device, the device always
forwards multicast traffic to these routers. For example, PIM sparse routers R1, R2 and R3 connect
through a device. Assume R2 needs traffic, and R1 sends it to the device, which forwards it to both
R2 and R3, even though R3 does not need it. A PIM SM snooping-enabled device listens to join and
prune messages exchanged by PIM sparse routers, and stops traffic to the router that sends prune
messages. This allows the device to forward the data stream to R2 only.