DM-NVX-E30(C)/DM-NVX-D30(C)/DM-NVX-D80-IOAV Product Manual – DOC. 8425B
IGMP Snooping
A DM NVX device sends IGMP join and leave messages.
NOTE: DM NVX devices support IGMPv2 and IGMPv3 only. IGMPv1 is not supported.
The IGMP snooping support version (v2 or v3) is configurable in the web interface.
The Network Interface section of the Network page allows the desired version to be
selected. The default setting is v2.
Network Page - Network Interface
NOTE: When a different IGMP snooping support version is selected, the DM NVX device
must be rebooted in order for the change to take effect.
The network switch port that connects to a DM NVX device must be enabled with
IGMPv2 or IGMPv3 snooping to prevent the switch from flooding the multicast
destination address traffic to all other connected ports. The multicast destination
address that is configured for the DM NVX device must be within the range of qualified
addresses. An upstream device such as a layer 3 router or switch periodically sends the
IGMP General Query messages to hosts in order to maintain group membership state
information. These queries can be either general or group-specific queries. The host
responds to queries with IGMP membership reports. The host running IGMPv2 or IGMPv3
may also send a Leave Group message to routers or switches in order to withdraw from
the group.
NOTES:
• DM NVX devices do not support random-timer and source-specific queries.
• As a host, a DM NVX device configured for support of IGMPv3 is compatible with a
network switch (IGMP querier) that is configured for IGMPv2.
IGMP snooping switches build forwarding lists by listening for and, in some cases,
intercepting IGMP messages. Although the software processing the IGMP messages may
maintain state information based on the full IP group addresses, the forwarding tables
are typically mapped to link layer addresses as shown in the following example.
Example of Forwarding Table
Because only the least significant 23 bits of the IP address are mapped to Ethernet
addresses (RFC 1112), there is a loss of information when forwarding solely on the
destination MAC address. For example, IP addresses 224.0.0.123 and 239.128.0.123 and
similar IP multicast addresses all map to MAC address 01-00-5e-00-00-7b for Ethernet.
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