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Using IGMP/MLD Proxy to replicate Multicast traffic on devices, such as the edge
boxes, can greatly simplify the design and implementation of these devices. By
not supporting more complicated Multicast routing protocols, such as Protocol
Independent Multicast (PIM) or Distance Vector Multicast Routing Protocol
(DVMRP), it reduces not only the cost of the devices, but also the operational
overhead. Another advantage is that it makes the proxy devices independent of
the Multicast routing protocol used by the core network routers. Hence, proxy
devices can be easily deployed in any Multicast network.
IGMP/MLD Proxy Tree
IGMP/MLD Proxy works in a simple tree topology in which it is not necessary to
run a robust Multicast routing protocol (for example, PIM). It is sufficient to use a
simple IPM Routing protocol based on learning group membership information and
proxy group membership information and forward Multicast packets based upon
that information.
The tree must be manually configured by designating upstream and downstream
interfaces on each proxy device. In addition, the IP addressing scheme applied to
the proxying tree topology should be configured to ensure that a proxy device can
win the IGMP/MLD Querier election to be able to forward Multicast traffic. There
should be no other Multicast routers except the proxy devices within the tree, and
the root of the tree is expected to be connected to a wider Multicast infrastructure.
A proxy device performing IGMP/MLD-based forwarding has a single upstream
interface and one or more downstream interfaces. These designations are
explicitly configured; there is no protocol to determine what type each interface is.
A proxy device performs the router portion of IGMP/MLD on its downstream
interfaces, and the host portion of IGMP/MLD on its upstream interface.
Only one tree is supported.
Forwarding Rules and Querier
The following rules are applied:
• A Multicast packet received on the upstream interface is forwarded on all
downstream interfaces requesting the packet only if the proxy device is the
querier on the interfaces.
• A proxy device drops Multicast packets received on a downstream
interface if it is not the querier on the interface.
• A Multicast packet received on a downstream interface on which the proxy
device is the querier is forwarded on the upstream interface and on all
Cisco 500 Series Managed Switch Administration Guide
Multicast
Multicast Forwarding