Cisco 350 Series Administration Manual page 347

Multicast
Multicast Forwarding Overview
Cisco 350, 350X and 550X Series Managed Switches, Firmware Release 2.4, ver 0.4
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 the upstream interface
- 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 downstream interfaces
requesting the packet only if the proxy device is the querier on the interfaces.
Downstream Interface Protection
By default, IP Multicast traffic arriving on an interface of the IGMP/MLD tree is forwarded.
You can disable of IP Multicast traffic forwarding arriving on downstream interfaces. It can be
done globally and on a given downstream interface.
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