User guide

Configuring a Multicast Border Router Multicast Border Router Overview
OmniSwitch AOS Release 7 Advanced Routing Configuration Guide March 2015 page 8-3
Multicast Border Router Overview
The multicast border router (MBR) functionality implemented for the OmniSwitch supports interoperabil-
ity between a PIM and DVMRP domain. Interoperability between PIM and other protocols or between
multiple PIM domains is not supported. In addition, PIM support refers only to PIM-DM and PIM-SM
(PIM-SSM is not supported).
Based on the RFC 2715 definition of multicast border router, an OmniSwitch MBR consists of a DVMRP
instance and a PIM instance with one or more active interfaces in each instance. In this role, the OmniS-
witch MBR performs the following primary functions:
• The MBR first pulls down packets generated within the PIM domain and injects them into the DVMRP
domain.
• The MBR then imports packets generated within the DVMRP domain so that they can be delivered to
group members inside the PIM domain, using PIM mechanisms.
• In the case of transit networks, the MBR passes the multicast traffic through the PIM and DVMRP
domains.
Multicast border router functionality is configured and enabled on an OmniSwitch that is located at points
where PIM and DVMRP regions interconnect. When MBR is operationally active, sources and receivers
from a DVMRP domain can communicate with sources and receivers inside a PIM domain.
DVMRP Overview
This section provides a brief overview of the OmniSwitch DVMRP implementation. For more detailed
information about using DVMRP, see Chapter 6, “Configuring DVMRP.”
Distance Vector Multicast Routing Protocol (DVMRP) Version 3 is a multicast routing protocol that
enables routers to efficiently propagate IP multicast traffic through a network. Multicast traffic consists of
a data stream that originates from a single source and is sent to hosts that have subscribed to that stream.
Live video broadcasts, video conferencing, corporate communications, distance learning, and distribution
of software, stock quotes, and news services are examples of multicast traffic. Multicast traffic is distin-
guished from unicast traffic and broadcast traffic as follows:
• Unicast traffic is addressed to a single host.
• Broadcast traffic is transmitted to all hosts.
• Multicast traffic is transmitted to a subset of hosts (the hosts that have subscribed to the multicast data
stream).
DVMRP is a distributed multicast routing protocol that dynamically generates per-source delivery trees
based upon routing exchanges, using a technique called Reverse Path Multicasting. When a multicast
source begins to transmit, the multicast data is flooded down the delivery tree to all points in the network.
DVMRP then prunes (i.e., removes branches from) the delivery tree where the traffic is unwanted.
Pruning continues to occur as group membership changes or routers determine that no group members are
present. This restricts the delivery trees to the minimum branches necessary to reach all group members,
thus optimizing router performance. New branches can also be added to the delivery trees dynamically as
new members join the multicast group. The addition of new branches is referred to as grafting.