# Configuring SSM Mapping

Source-specific multicast (SSM) mapping enables the router to determine one or more source addresses for group G. The mapping effectively translates IGMPv1 or IGMPv2 membership reports to an IGMPv3 report, enabling the router to continue as if it had initially received an IGMPv3 report. After the router is joined to these groups, it sends out PIM join messages and continues to enable joining from these groups, as long as it continues to receive IGMPv1 and IGMPv2 membership reports and no change occurs to the SSM mapping for the group.

When you statically configure SSM mapping, the router can discover source addresses from a statically configured table.

The following conditions apply when you configure SSM mapping:

- When SSM mapping is enabled, and either you have not configured a static SSM map or the router cannot find any matching access lists, the router continues to accept (*,G) groups. The PIM SSM range must deny any unacceptable SSM group addresses.
- When you issue the no ip igmp ssm-map enable command, the router removes all SSM map (S,G) states and establishes a (*,G) state.
- You can enter multiple ssm-map static commands for different access lists. Also, you can enter multiple ssm-map static commands for the same access list, as long as the access list uses different source addresses.
- SSM maps do not process statically configured groups.

ip igmp ssm-map enable

- Use to enable SSM mapping on the router. SSM mapping statically assigns sources to IGMPv1 and IGMPv2 groups. You must use SSM mapping for IGMPv1 and IGMPv2 hosts to interoperate with PIM SSM. SSM mapping enables the router to use a statically configured list to translate (*,G) memberships to (S,G) memberships.
- Example
  host1:boston(config)#ip igmp ssm-map enable
- Use the no version to disable SSM mapping on the router.
- See ip igmp ssm-map enable.

ip igmp ssm-map static

- Use to specify an access list and source address for use in SSM mapping. SSM mapping statically assigns sources to IGMPv1 and IGMPv2 groups. You must use SSM mapping for IGMPv1 and IGMPv2 hosts to interoperate with PIM SSM. SSM mapping enables the router to use a statically configured list to translate (*,G) memberships to (S,G) memberships.
- Example
  host1:boston(config)#ip igmp ssm-map static boston-list 51.0.0.1
- Use the no version to remove the SSM map association.
- See ip igmp ssm-map static.