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# Enabling IGMP on an Interface

You must start IGMP on each interface that you want to use the protocol. You can configure IGMP and either PIM or DVMRP on the same interface. If you configure only IGMP on an interface, IGMP owns that interface. If you configure IGMP and either PIM or DVMRP on an interface, PIM or DVMRP owns the interface.

By enabling IGMP, the router processes incoming multicast packets and creates an entry in the multicast routing table. If neither PIM nor DVMRP own the interface (for example, when only IGMP is configured), then the packets are locally routed to other interfaces on the router. PIM or DVMRP must be configured on the interface for packets to be sent to other routers.

For networks that use only IGMPv1, you can configure an interface to operate in IGMPv1 mode. However, IGMPv2 and IGMPv3 interfaces support IGMPv1 hosts. In an IGMPv1 network, you must configure one interface to act as a querier. In an IGMPv2 or IGMPv3 network, the querier is the router with the lowest IP address.

To start IGMP, complete the following steps:

1. Enable IGMP on the interface (IGMPv2 is the default version).
2. (IGMPv1 or IGMPv3) Specify the IGMP version for the interface.
3. (IGMPv1 only) Specify that the interface act as the querier for the network.

ip igmp

- Use to enable IGMP on an interface and to set the IGMP version to IGMPv2. Use the ip igmp version command to specify a different IGMP version.
- Example
  `
  host1:boston(config-if)#ip igmp
  `
- Use the no version to disable IGMP on an interface.
- See ip igmp.

ip igmp querier

- Use to specify that this IGMPv1 interface acts as a querier.

  | Note: This command is valid only for interfaces on which you configured IGMPv1.

- By default, IGMPv1 interfaces act as queriers.
- Example
  `
  host1:boston(config-if)#ip igmp querier
  `
- Use the no version to cause the interface to not act as a querier.
- See ip igmp querier.

ip igmp version

- Use to set the IGMP version (1, 2, or 3) for the interface or specify a passive interface with only multicast-data-forwarding capability (passive).
- Example
  `
  host1:boston(config-if)#ip igmp version 1
  `
- Use the no version to set the version to the default, IGMPv2.
- See ip igmp version.

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