Configuring MLD Limit

Pre-configuration Tasks

Context

As defined, group members can join or leave a multicast group at any time and any place, and the number of members is not limited. When many users watch multiple programs simultaneously, a lot of bandwidth on the multicast device is consumed, leading to degradation of device performance. To prevent this problem, you can configure Multicast Listener Discovery (MLD) limit on the multicast switch to limit the number of multicast groups on an interface or in the system. This ensures that users watch clear, stable programs. When the multicast switch receives a Multicast Listener Report message, the switch first checks whether the number of multicast groups exceeds the maximum value if the new multicast group is added. If not, the multicast member is added to the multicast group and the multicast data is forwarded to the member.

The switch counts MLD entries as follows:

Counts each (*, G) entry as one entry.
Counts each (S, G) entry as one entry.
Counts each (*, G) entry used in MLD SSM mapping as one entry but does not count (S, G) entries converted from (*, G) entries.

You can configure the maximum number of MLD group members in the system and MLD views. If the configurations in the system and MLD views are both performed, the smaller value takes effect.
To configure MLD limit in the system and interface views of the switch, you are advised to set a larger maximum number of MLD group members in the system view.

Procedure

Configuring a global limit on the number of MLD entries in the system view
1. Run system-view
  The system view is displayed.
2. Run mld global limit number
  The maximum number of MLD entries allowed in the system is configured.
Configuring a global limit on the number of MLD entries in the MLD view
1. Run system-view
  The system view is displayed.
2. Run mld
  The MLD view is displayed.
3. Run limit number
  The maximum number of MLD entries allowed in the system is configured.
Configuring the MLD limit on an interface
1. Run system-view
  The system view is displayed.
2. Run interface interface-type interface-number
  The interface view is displayed.
3. (Optional) On an Ethernet interface, run undo portswitch
  The interface is switched to Layer 3 mode.
  
  By default, an Ethernet interface works in Layer 2 mode.
  
  Only the S5720-EI, S5720-HI, S5730-HI, S5731-H, S5731-S, S5731S-H, S5731S-S, S5732-H, S6720-EI, S6720-HI, S6720S-EI, S6730-H, S6730S-H, S6730-S, and S6730S-S support switching between Layer 2 and Layer 3 modes.
4. Run mld limit number [ except acl6-number ]
  The maximum number of MLD entries allowed on the interface is configured.
  
  If except is not specified in the command, the number of entries for all the groups or sources/groups dynamically created on the switch is limited by the maximum number of MLD entries.
  
  Before setting except, you need to configure the associated IPv6 access control list (ACL6). The interface then filters the received MLD Report messages according to the ACL6. The number of entries specified to be filtered by the ACL6 is not limited by the maximum number of MLD entries.

Verifying the Configuration

Run the display mld interface [ interface-type interface-number | up | down ] [ verbose ] command to check the MLD information on an interface.