VSAN-Troubleshooting-Reference-Manual

Diagnostics and Troubleshooting Reference Manual – Virtual SAN
IGMP snooping and IGMP querier for multicast traffic
Multicast forwarding is a one-to-many or many-to-many distribution of network
traffic (as opposed to unicast’s one-to-one forwarding scheme). Rather than using
the network address of the intended recipient for its destination address, multicast
uses a special destination address to logically identify a group of receivers.
Since multicasting allows the data to be sent only once, this has the benefit of freeing
up computing resources from the source ESXi host. As was just mentioned, without
multicast, that host would need to send individual streams of duplicate data to all of
the other ESXi hosts in the cluster. Leveraging switching technology to repeat the
message to the members of the multicast group is far more efficient for the host
than it is sending each individually.
Many network administrators do not want to enable multicast across network
switches, for good reason. This can generate a large volume of traffic on the
network, since each network device attached to an active network port would
receive the multicast network traffic. To avoid this, many network administrators
use IGMP, the Internet Group Management Protocol. IGMP is a communications
protocol used to establish multicast group memberships. IGMP Snooping and an
IGMP Querier can be leveraged to send multicast traffic to a subset of switch ports
that have devices attached that request it. This will avoid causing unnecessary load
on other network devices as they will not have to process packets that they have not
solicited.
VMware highly recommends the use of IGMP snooping with IGMP Querier which
should be available on most physical switches. This will avoid the multicast traffic
flooding across all ports of the switch. Multicast traffic can be limited to specific
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