Cisco Catalyst 3850 series Configuration Manual page 127

Configuring IGMP Proxy
Scenario 1--Traditional UDLR Scenario (UDL Device with Directly Connected Receivers)
For scenario 1, no IGMP proxy mechanism is needed. In this scenario, the following sequence of events
occurs:
1 User 2 sends an IGMP membership report requesting interest in group G.
2 Router B receives the IGMP membership report, adds a forwarding entry for group G on LAN B, and
proxies the IGMP report to Router A, which is the UDLR upstream device.
3 The IGMP report is then proxied across the Internet link.
4 Router A receives the IGMP proxy and maintains a forwarding entry on the unidirectional link.
Scenario 2--IGMP Proxy Scenario (UDL Device without Directly Connected Receivers)
For scenario 2, the IGMP proxy mechanism is needed to enable hosts that are not directly connected to a
downstream device to join a multicast group sourced from an upstream network. In this scenario, the following
sequence of events occurs:
1 User 1 sends an IGMP membership report requesting interest in group G.
2 Router C sends a PIM Join message hop-by-hop to the RP (Router B).
3 Router B receives the PIM Join message and adds a forwarding entry for group G on LAN B.
4 Router B periodically checks its mroute table and proxies the IGMP membership report to its upstream
UDL device across the Internet link.
OL-32598-01
IP Multicast Routing Configuration Guide, Cisco IOS XE Release 3.6E (Catalyst 3850 Switches)
IGMP Proxy
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