• All devices on the IGMP UDL have the same subnet address. If all devices on the UDL cannot have the same subnet address, the upstream device must be configured with secondary addresses to match all of the subnets to which the downstream devices are attached.

• IP multicast is enabled and the PIM interfaces are configured.

  Note

  Use the following guidelines when configuring PIM interfaces for IGMP proxy: Use PIM sparse mode (PIM-SM) when the interface is operating in a sparse-mode region and you are running static RP, bootstrap (BSR), or Auto-RP with the Auto-RP listener capability. Use PIM sparse-dense mode when the interface is running in a sparse-dense mode region and you are running Auto-RP without the Auto-RP listener capability. Use PIM dense mode (PIM-DM) when the interface is operating in dense mode and is, thus, participating in a dense-mode region. Use PIM-DM with the proxy-register capability when the interface is receiving source traffic from a dense-mode region that needs to reach receivers that are in a sparse-mode region.

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.

5. Router A creates and maintains a forwarding entry on the unidirectional link (UDL).

In an enterprise network, it is desirable to be able to receive IP multicast traffic via satellite and forward the traffic throughout the network. With unidirectional link routing (UDLR) alone, scenario 2 would not be possible because receiving hosts must be directly connected to the downstream device, Router B. The IGMP proxy mechanism overcomes this limitation by creating an IGMP report for (*, G) entries in the multicast forwarding table. To make this scenario functional, therefore, you must enable IGMP report forwarding of proxied (*, G) multicast static route (mroute) entries (using the ip igmp mroute-proxy command) and enable the mroute proxy service (using the ip igmp proxy-service command) on interfaces leading to PIM-enabled networks with potential members.

Note	Because PIM messages are not forwarded upstream, each downstream network and the upstream network have a separate domain.

Perform this task to configure the upstream UDL device for IGMP UDLR.

Perform this task to configure the downstream UDL device for IGMP UDLR with IGMP proxy support.

The following example shows how to configure the upstream UDL device for IGMP UDLR and the downstream UDL device for IGMP UDLR with IGMP proxy support.

Upstream Device Configuration

interface gigabitethernet 0/0/0 
ip address 10.1.1.1 255.255.255.0 
ip pim dense-mode 
! 
interface gigabitethernet 1/0/0 
ip address 10.2.1.1 255.255.255.0 
ip pim dense-mode 
ip igmp unidirectional-link 
! 
interface gigabitethernet 2/0/0 
ip address 10.3.1.1 255.255.255.0 

Downstream Device Configuration

ip pim rp-address 10.5.1.1 5 
access-list 5 permit 239.0.0.0 0.255.255.255 
! 
interface loopback 0 
ip address 10.7.1.1 255.255.255.0 
ip pim dense-mode 
ip igmp helper-address udl ethernet 0 
ip igmp proxy-service 
! 
interface gigabitethernet 0/0/0 
ip address 10.2.1.2 255.255.255.0 
ip pim dense-mode 
ip igmp unidirectional-link 
! 
interface gigabitethernet 1/0/0 
ip address 10.5.1.1 255.255.255.0 
ip pim sparse-mode 
ip igmp mroute-proxy loopback 0 
! 
interface gigabitethernet 2/0/0 
ip address 10.6.1.1 255.255.255.0 

The following sections provide references related to customizing IGMP.

Related Documents

Standards and RFCs

MIBs

Technical Assistance