Mvpn Overview; Multicast Routing And Forwarding And Multicast Domains; Multicast Distribution Trees - Cisco 7604 Configuration Manual

Understanding How MVPN Works

MVPN Overview

MVPN is a standards-based feature that transmits IPv4 multicast traffic across an MPLS VPN cloud.
MVPN on Cisco 7600 series routers uses the existing PFC hardware support for IPv4 multicast traffic to
forward multicast traffic over VPNs at wire speeds. MVPN adds support for IPv4 multicast traffic over
Layer 3 IPv4 VPNs to the existing IPv4 unicast support.
MVPN routes and forwards multicast packets for each individual VPN routing and forwarding (VRF)
instance, as well as transmitting the multicast packets through VPN tunnels across the service provider
backbone.
MVPN is an alternative to IP-in-IP generic route encapsulation (GRE) tunnels. GRE tunnels are not a
readily scalable solution and they are limited in the granularity they provide to customers.

Multicast Routing and Forwarding and Multicast Domains

MVPN adds multicast routing information to the VPN routing and forwarding table. When a
provider-edge (PE) router receives multicast data or control packets from a customer-edge (CE) router,
forwarding is performed according to the information in the multicast VRF (MVRF).
Note MVRF is also commonly referred to as multicast over VRF-lite.
Each MVRF maintains the routing and forwarding information that is needed for its particular VRF
instance. An MVRF is created and configured in the same way as existing VRFs, except multicast
routing is also enabled on each MVRF.
A multicast domain constitutes the set of hosts that can send multicast traffic to each other within the
MPLS network. For example, the multicast domain for a customer that wanted to send certain types of
multicast traffic to all global employees would consist of all CE routers associated with that enterprise.

Multicast Distribution Trees

The MVPN feature establishes at least one multicast distribution tree (MDT) for each multicast domain.
The MDT provides the information needed to interconnect the same MVRFs that exist on the different
PE routers.
MVPN supports two MDT types:
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Default MDT—The default MDT is a permanent channel for PIM control messages and
low-bandwidth streams between all PE routers in a particular multicast domain. All multicast traffic
in the default MDT is replicated to every other PE router in the domain. Each PE router is logically
seen as a PIM neighbor (one hop away) from every other PE router in the domain.
Data MDT—Data MDTs are optional. If enabled, they are dynamically created to provide optimal
paths for high-bandwidth transmissions, such as full-motion video, that do not need to be sent to
every PE router. This allows for on-demand forwarding of high-bandwidth traffic between PE
routers, so as to avoid flooding every PE router with every high-bandwidth stream that might be
created.
Chapter 25 Configuring IPv4 Multicast VPN Support
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