Administrator Guide

1582 IPv4 and IPv6 Multicast
What Are the Multicast Protocol Roles?
Hosts must have a way to identify their interest in joining any particular
multicast group, and routers must have a way to collect and maintain group
memberships. These functions are handled by the IGMP protocol in IPv4. In
IPv6, multicast routers use the Multicast Listener Discover (MLD) protocol
to maintain group membership information.
Multicast routers must also be able to construct a multicast distribution tree
that enables forwarding multicast datagrams only on the links that are
required to reach a destination group member. Protocols such as DVMRP, and
PIM handle this function.
IGMP and MLD are multicast group discovery protocols that are used
between the clients and the local multicast router. PIM-SM, PIM-DM, and
DVMRP are multicast routing protocols that are used across different
subnets, usually between the local multicast router and remote multicast
router.
When Is L3 Multicast Required on the Switch?
Use the IPv4/IPv6 multicast feature on Dell EMC Networking N-Series
switches to route multicast traffic between VLANs on the switch. If all hosts
connected to the switch are on the same subnet, there is no need to configure
the IP/IPv6 multicast feature. If the switch does not require L3 routing,
IGMP snooping or MLD snooping can be used to manage port-based
multicast group membership. For more information, see "What Is IGMP
Snooping?" on page 927 and "What Is MLD Snooping?" on page 929. If the
local network does not have a multicast router, the switch can be configured
to act as the IGMP querier. For more information, see "IGMP Snooping
Querier" on page 929.
If the switch is configured as an L3 switch and handles inter-VLAN routing
through static routes, OSPF, or RIP, and multicast traffic is transmitted
within the network, enabling and configuring L3 multicast routing on the
switch is recommended.
By default, multicast packets locally routed into a VLAN by the router are
flooded to all ports in the VLAN. Multicast packets ingressing a port that is a
member of a routed VLAN are flooded to all ports in the VLAN other than
the receiving port. Although IGMP/MLD snooping can be used to mitigate
this behavior, it is strongly recommended that multicast routed VLANs only