MLD

Overview

MLD is an asymmetric protocol used by IPv6 routers to discover the presence of multicast listeners, that is, NEs that wish to receive multicast packets. MLD specifies separate behaviors for multicast address listeners and multicast routers.

The purpose of MLD is to enable each multicast router to discover, for each of its directly attached links, which multicast addresses and which sources have interested listeners on that link. The information gathered by MLD is provided to whichever multicast routing protocol is used by the router, such as PIM, to ensure that multicast packets are delivered to all links where there are listeners interested in such packets.

An MLD group interface is configurable on a base routing instance, VPRN routing instance, and on an IES site. To allow the delivery of IPv6 multicast content to subscribers, group interfaces are configurable under MLD. MLD report/done/query messages use the link-local address as their source address. An MLD policy is applied to the subscriber profile to allow unique behavior per subscriber.

To support MCS for subscribers using MLD, MLD information is synced across chassis. During a failover scenario, standby MLD becomes active and PIM sends a join message to all necessary multicast sources.

MLD is supported on the 7950 XRS, in chassis mode C or D, and on the 7750 SR in chassis mode A or B with mixed mode enabled. MLD is supported on all variants of the 7705 SAR.

MLD under IES and VPRN is supported on the 7950 XRS, the 7750 SR in chassis mode D, and the 7450 ESS in chassis mode D with mixed mode enabled.