MLD Snooping
When IGMP/MLD snooping is enabled in a switch on a VLAN, it analyzes the IGMP/ MLD packets it receives from the VLAN connected to the switch and from the Multicast routers in the network.
When a switch learns that a host is using IGMP/MLD messages to register to receive a Multicast stream, optionally from a specific source, the switch adds the registration in its Multicast Forwarding Data Base.
IGMP/MLD snooping can effectively reduce Multicast traffic from streaming bandwidth-intensive IP applications. A switch using IGMP/MLD snooping only forwards Multicast traffic to the hosts interested in that traffic. This reduction of Multicast traffic reduces the packet processing at the switch, and also reduces the workload at the end hosts, since they do not have to receive and filter all of the Multicast traffic generated in the network.
The following versions are supported:
To support selective Multicast forwarding (IPv6), Bridge Multicast filtering must be enabled, and MLD Snooping must be enabled globally and for each relevant VLAN.
NOTE The switch supports MLD Snooping only on static VLANs. It does not support MLD Snooping on dynamic VLANs
The switch uses this feature to build Multicast membership lists. It uses the lists to forward Multicast packets only to switch ports where there are host nodes that are members of the Multicast groups. The switch does not support MLD Querier.
Hosts use the MLD protocol to report their participation in Multicast sessions.
Additional Information
The switch supports two versions of MLD snooping:
The actual MLD version is selected by the Multicast router in the network.
In an approach similar to IGMP snooping, MLD frames are snooped as they are forwarded by the switch from stations to an upstream Multicast router and vice versa. This facility enables a switch to conclude the following:
This knowledge is used to exclude irrelevant ports (ports on which no stations have registered to receive a specific Multicast group) from the forwarding set of an incoming Multicast frame.
If you enable MLD snooping in addition to the manually-configured Multicast groups, the result is a union of the Multicast groups and port memberships derived from the manual setup and the dynamic discovery by MLD snooping. Only static definitions are preserved when the system is rebooted.
To enable MLD Snooping:
- Click Multicast > MLD Snooping. The MLD Snooping page opens.
- Enable or disable MLD Snooping Status. When MLD Snooping is globally enabled, the device monitoring network traffic can determine which hosts have requested to receive Multicast traffic. The switch performs MLD Snooping only if both MLD snooping and Bridge Multicast filtering are enabled.
- Select a VLAN, and click Edit. The Edit MLD Snooping page opens.
- Enter the parameters.
- VLAN ID--Select the VLAN ID.
- MLD Snooping Status--Enable or disable MLD snooping on the VLAN. The switch monitors network traffic to determine which hosts have asked to be sent Multicast traffic. The switch performs MLD snooping only when MLD snooping and Bridge Multicast filtering are both enabled
- Operational MLD Snooping Status--Displays the current status of MLD Snooping for the selected VLAN.
- MRouter Ports Auto-Learn--Enable or disable Auto Learn for the Multicast router.
- Query Robustness--Enter the Robustness Variable value to be used if the switch cannot read this value from messages sent by the elected querier.
- Operational Query Robustness--Displays the robustness variable sent by the elected querier.
- Query Interval--Enter the Query Interval value to be used by the switch if the switch cannot derive the value from the messages sent by the elected querier.
- Operational Query Interval--The time interval in seconds between General Queries received from the elected querier.
- Query Max Response Interval--Enter Query Max Response delay to be used if the switch cannot read the Max Response Time value from General Queries sent by the elected querier.
- Operational Query Max Response Interval--Displays the delay used to calculate the Maximum Response Code inserted into the General Queries.
- Last Member Query Counter--Enter the Last Member Query Count to be used if the switch cannot derive the value from the messages sent by the elected querier.
- Operational Last Member Query Counter--Displays the operational value of the Last Member Query Counter.
- Last Member Query Interval--Enter the Maximum Response Delay to be used if the switch cannot read Max Response Time value from Group-Specific queries sent by the elected querier.
- Operational Last Member Query Interval--The Last Member Query Interval sent by the elected querier.
- Immediate Leave--When enabled, reduces the time it takes to block unnecessary MLD traffic sent to a switch port.
- Click Apply. The Running Configuration file is updated..