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Enabling MLD

The Multicast Listener Discovery (MLD) Protocol manages multicast groups by establishing, maintaining, and removing groups on a subnet. Multicast routing devices use MLD to learn which groups have members on each of their attached physical networks. MLD must be enabled for the router to receive IPv6 multicast packets. MLD is only needed for IPv6 networks, because multicast is handled differently in IPv4 networks. MLD is enabled on all IPv6 interfaces on which you configure PIM and on all IPv6 broadcast interfaces when you configure DVMRP.

MLD specifies different behaviors for multicast listeners and for routers. When a router is also a listener, the router responds to its own messages. If a router has more than one interface to the same link, it needs to perform the router behavior over only one of those interfaces. Listeners, on the other hand, must perform the listener behavior on all interfaces connected to potential receivers of multicast traffic.

If MLD is not running on an interface—either because PIM and DVMRP are not configured on the interface or because MLD is explicitly disabled on the interface—you can explicitly enable MLD.

To explicitly enable MLD:

  1. If PIM and DVMRP are not running on the interface, explicitly enable MLD by including the interface name.
    [edit protocols mld]user@host# set interface fe-0/0/0.0
  2. Check to see if MLD is disabled on any interfaces. In the following example, MLD is disabled on a Gigabit Ethernet interface.
    [edit protocols mld]user@host# show
    interface fe-0/0/0.0;
interface ge-0/0/0.0 {
    disable;
}
  3. Enable MLD on the interface by deleting the disable statement.
    [edit protocols mld]delete interface ge-0/0/0.0 disable
  4. Verify the configuration.
    [edit protocols mld]user@host# show
    interface fe-0/0/0.0;
interface ge-0/0/0.0;
  5. Verify the operation of MLD by checking the output of the show mld interface command.
 

Related Documentation

 

Published: 2012-06-29

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