Users Guide

Table Of Contents
IPv4 and IPv6 Multicast 1597
What Is MLD?
Multicast Listener Discovery (MLD) protocol enables IPv6 routers to
discover the presence of multicast listeners, the hosts that wish to receive the
multicast data packets, on its directly-attached interfaces. The protocol
specifically discovers which multicast addresses are of interest to its
neighboring nodes and provides this information to the active multicast
routing protocol that makes decisions on the flow of multicast data packets.
MLD is automatically enabled whenever IPv6 PIM is enabled on IPv6
interfaces via the CLI.
The Multicast router sends General Queries periodically to request multicast
address listeners information from systems on an attached network. These
queries are used to build and refresh the multicast address listener state on
attached networks. Multicast listeners respond to these queries by reporting
their multicast addresses listener state and their desired set of sources with
Current-State Multicast address Records in the MLD2 Membership Reports.
The Multicast router also processes unsolicited Filter-Mode-Change records
and Source-List-Change Records from systems that want to indicate interest
in receiving or not receiving traffic from particular sources.
The Dell EMC Networking implementation of MLD v2 supports the
multicast router portion of the protocol (i.e., not the listener portion). It is
backward-compatible with MLD v1.
What Is PIM?
The Protocol Independent Multicast protocol is a simple, protocol-
independent multicast routing protocol. PIM uses an existing unicast routing
table and a Join/Prune/Graft mechanism to build a tree. Dell EMC
Networking N-Series switches support two types of PIM: sparse mode (PIM-
SM) and dense mode (PIM-DM).
PIM-SM is most effective in networks with a sparse population of multicast
receivers. In contrast, PIM-DM is most effective in networks with densely
populated multicast receivers. In other words, PIM-DM can be used if the
majority of network hosts request to receive a multicast stream, while PIM-
SM might be a better choice in networks in which a small percentage of
network hosts, located throughout the network, wish to receive the multicast
stream.