Multicast Distribution Trees; Source Trees - Cisco Nexus 7000 Series Configuration Manual

Multicast Distribution Trees

Note For a complete list of RFCs related to multicast, see
The routers in the network listen for receivers to advertise their interest in receiving multicast data from
selected groups. The routers then replicate and forward the data from sources to the interested receivers.
Multicast data for a group is transmitted only to those LAN segments with receivers that requested it.
This figure shows one source transmitting multicast data that is delivered to two receivers. In the figure,
because the center host is on a LAN segment where no receiver requested multicast data, no data is delivered
to that receiver.
Figure 1: Multicast Traffic from One Source to Two Receivers
Multicast Distribution Trees
A multicast distribution tree represents the path that multicast data takes between the routers that connect
sources and receivers. The multicast software builds different types of trees to support different multicast
methods.

Source Trees

A source tree represents the shortest path that the multicast traffic takes through the network from the sources
that transmit to a particular multicast group to receivers that requested traffic from that same group. Because
of the shortest path characteristic of a source tree, this tree is often referred to as a shortest path tree (SPT).
This figure shows a source tree for group 224.1.1.1 that begins at host A and connects to hosts B and C.
Cisco Nexus 7000 Series NX-OS Multicast Routing Configuration Guide
4
Appendix A, "IETF RFCs for IP Multicast."
Overview