Igmp Versions; Joining A Multicast Group - Cisco Catalyst 3120 Software Manual

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Configuring IGMP Snooping and MVR

IGMP Versions

The switch supports IGMP Version 1, IGMP Version 2, and IGMP Version 3. These versions are

interoperable on the switch. For example, if IGMP snooping is enabled on an IGMPv2 switch and the

switch receives an IGMPv3 report from a host, the switch can forward the IGMPv3 report to the

multicast router.

The switch supports IGMPv3 snooping based only on the destination multicast MAC address. It does not

support snooping based on the source MAC address or on proxy reports.

An IGMPv3 switch supports Basic IGMPv3 Snooping Support (BISS), which includes support for the

snooping features on IGMPv1 and IGMPv2 switches and for IGMPv3 membership report messages.

BISS constrains the flooding of multicast traffic when your network includes IGMPv3 hosts. It

constrains traffic to approximately the same set of ports as the IGMP snooping feature on IGMPv2 or

IGMPv1 hosts.

IGMPv3 join and leave messages are not supported on switches running IGMP filtering or MVR.

An IGMPv3 switch can receive messages from and forward messages to a device running the Source

Specific Multicast (SSM) feature. For more information about source-specific multicast with IGMPv3

and IGMP, see this URL:

http://www.cisco.com/en/US/products/sw/iosswrel/ps1834/products_feature_guide09186a008008048a.

When a blade server connected to the switch wants to join an IP multicast group and it is an IGMP

Version 2 client, it sends an unsolicited IGMP join message, specifying the IP multicast group to join.

Alternatively, when the switch receives a general query from the router, it forwards the query to all ports

in the VLAN. IGMP Version 1 or Version 2 blade servers wanting to join the multicast group respond

by sending a join message to the switch. The switch CPU creates a multicast forwarding-table entry for

the group if it is not already present. The CPU also adds the interface where the join message was

received to the forwarding-table entry. The blade server associated with that interface receives multicast

traffic for that multicast group. See

Cisco Catalyst Blade Switch 3120 for HP Software Configuration Guide

Understanding IGMP Snooping

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