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Configuring Unidirectional Link Routing
IGMP UDLR Configuration Task List
IPC-510
Cisco IOS IP Configuration Guide
IGMP UDLR Configuration Task List
To configure IGMP UDLR, perform the tasks described in the following sections. The tasks in the first
section are required; the tasks in the remaining sections are optional.
• Configuring the IGMP UDL (Required)
• Changing the Distance for the Default RPF Interface (Optional)
• Monitoring IGMP UDLR (Optional)
Prerequisites
Before configuring IGMP UDLR, ensure that the following conditions exist:
• All routers on the UDL have the same subnet address. If all routers on the UDL cannot have the same
subnet address, the upstream router must be configured with secondary addresses to match all the
subnets that the downstream routers are attached to.
• Multicast receivers are directly connected to the downstream routers.
Configuring the IGMP UDL
To configure an IGMP UDL, you must configure both the upstream and downstream routers to meet the
following conditions:
• You need not specify whether the direction is sending or receiving; IGMP learns the direction by the
nature of the physical connection.
• When the downstream router receives an IGMP report from a host, the router helpers the report to
the IGMP querier associated with the UDL interface identified in the ip igmp helper-address
interface configuration command.
To configure the IGMP UDL on the upstream router, use the following command in interface
configuration mode:
To configure the IGMP UDL on the downstream router, use the following commands in interface
configuration mode:
Command Purpose
Router(config-if)# ip igmp unidirectional-link
Configures IGMP on the interface to be unidirectional.
Command Purpose
Step 1
Router(config-if)# ip igmp
unidirectional-link
Configures IGMP on the interface to be unidirectional.
Step 2
Router(config-if)# ip igmp
helper-address udl type number
Configures the interface to be an IGMP helper. Use this command
on every downstream router, on every interface to a potential
multicast receiver. Specify the type and number values that identify
the UDL interface.