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# Specifying Multicast Groups

You can use a standard-format or extended-format IP access list to specify the multicast groups that a host can join.

ip igmp access-group

- Use to restrict hosts on this subnetwork to join only multicast groups that appear on the specified IP access list.
- When this feature is configured, the access list is queried whenever the router receives an IGMPv2 report requesting membership of a group, and IGMPv3 ChangeToInclude or IsExclude reports. The request is rejected if the access list query fails.
- The ip igmp access-group command accepts standard or extended-format access lists. Because the extended format enables you to specify both the source address and the destination group address, the source address must be set to any. For example, access-list test permit ip host 224.128.64.32 any.
- Note that in the access list specified when you issue this command, the group is specified before the source.
- Example
  `
  host1:boston(config-if)#ip igmp access-group boston-list
  `
- Use the no version to dissociate the interface from an access list and to enable hosts on the interface to join any multicast group.
- See ip igmp access-group.

ip igmp access-source-group

- Use to restrict hosts on this subnetwork to membership in those (S,G) pairs (also known as channels) included on the specified IP access list.
- When this feature is configured, both source and group addresses query the associated access list whenever the router receives an IGMPv3 report requesting membership of the (S,G) pairs (that is, the router receives an IGMPv3 ChangeToInclude, IsInclude, or AllowNewSource group report). The request is rejected if the access list query fails.
- The ip igmp access-source-group command accepts standard or extended-format access lists. The extended format enables you to specify both the source address and the destination group address; for example, access-list test permit ip host 10.1.1.1 host 224.128.64.32. Typically, you use the extended-format access list. If you instead use the standard-format access list, you explicitly specify the source address to create the access list, but the group address is implicitly assumed to be any,
- Note that in the access list specified when you issue this command, the source is specified before the group.
- Example
  `
  host1:boston(config-if)#ip igmp access-source-group dallas-list
  `
- Use the no version to remove any access list restriction.
- See ip igmp access-source-group.

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