Quick Reference Guide

440 PowerConnect B-Series TI24X Configuration Guide
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IGMP snooping overview
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IGMP protocols provide a method for clients and a device to exchange messages, and let the device
build a database indicating which port wants what traffic. The protocols do not specify forwarding
methods. They require IGMP snooping or multicast protocols such as PIM to handle packet
forwarding. PIM can route multicast packets within and outside a VLAN, while IGMP snooping can
switch packets only within a VLAN.
If a VLAN is not IGMP snooping-enabled, it floods multicast data and control packets to the entire
VLAN in hardware. When snooping is enabled, IGMP packets are trapped to the CPU. Data packets
are mirrored to the CPU in addition to being VLAN flooded. The CPU then installs hardware
resources, so that subsequent data packets can be switched to desired ports in hardware without
going to the CPU. If there is no client report or port to queriers for a data stream, the hardware
resource drops it.
On PowerConnect B-Series TI24Xdevices, the hardware can either match the group address only (*
G), or both the source and group (S G) of the data stream. If any IGMPv3 is configured in any port of
a VLAN, this VLAN uses (S G) match; otherwise, it uses (* G). This is 32-bit IP address matching, not
23-bit multicast MAC address 01-00-5e-xx-xx-xx matching.
PowerConnect B-Series TI24Xdevices support up to 2K of IGMP groups, which are produced by
client membership reports.
IGMP V1, V2, and V3 snooping support
Table 73 shows IGMP snooping version support by software release on PowerConnect B-Series
TI24X devices.
Queriers and non-queriers
An IGMP snooping-enabled 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 -enabled port on another router, the VLAN should be configured as a
non-querier. When multiple IGMP snooping devices are connected together, and there is no
connection to a PIM-enabled port, one of the devices should 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, Dell 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 hellos. Dell 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.
TABLE 73 IGMP snooping support
Software release IGMP version support Supported in software code...
PowerConnect B-Series TI24X devices IGMP V1 snooping
IGMP V2 snooping
IGMP V3 snooping
L2