Cisco NX-OS supports multicasting with Protocol
Independent Multicast (PIM) sparse mode. PIM is IP routing protocol independent
and can leverage whichever unicast routing protocols are used to populate the
unicast routing table. In PIM sparse mode, multicast traffic is sent only to
locations of the network that specifically request it. PIM dense mode is not
In this publication, the term
“PIM” is used for PIM sparse mode version 2.
To access multicast commands,
you must enable the PIM feature.
Multicast is enabled only after you enable PIM on an interface
of each router in a domain. You can configure PIM for an IPv4 network. By default, IGMP is running on the system.
PIM, which is used between
multicast-capable routers, advertises group membership across a routing domain
by constructing multicast distribution trees. PIM builds shared distribution
trees, on which packets from multiple sources are forwarded, as well as source
distribution trees, on which packets from a single source are forwarded.
The distribution trees change
automatically to reflect the topology changes due to link or router failures.
PIM dynamically tracks both multicast-capable sources and receivers.
The router uses the unicast
routing table and RPF routes for multicast to create multicast routing
In this publication, “PIM for
IPv4” refers to the
Cisco NX-OS implementation of PIM sparse mode.
This figure shows two PIM
domains in an IPv4 network.
Figure 5. PIM Domains in
an IPv4 Network
The lines with
arrows show the path of the multicast data through the network. The multicast
data originates from the sources at hosts A and D.
The dashed line
connects routers B and F, which are Multicast Source Discovery Protocol (MSDP)
peers. MSDP supports the discovery of multicast sources in other PIM domains.
Hosts B and C
receive multicast data by using Internet Group Management Protocol (IGMP) to
advertise requests to join a multicast group.
Routers A, C, and
D are designated routers (DRs). When more than one router is connected to a LAN
segment, such as C and E, the PIM software chooses one router to be the DR so
that only one router is responsible for putting multicast data on the segment.
Router B is the
rendezvous point (RP) for one PIM domain, and router F is the RP for the other
PIM domain. The RP provides a common point for connecting sources and receivers
within a PIM domain.
PIM supports these
multicast modes for connecting sources and receivers:
You can also define RPF routes for multicast.