Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/​go/​cfn. An account on Cisco.com is not required.

The Support for Multiple Registrars on SIP trunks feature has the following restrictions:

• Old and new forms of the registrar command are mutually exclusive: the registrar can be configured in either primary/secondary mode or multiple registrar mode--not both.

• Dynamic Host Configuration Protocol (DHCP) support is not available with multiple registrars (available for primary/secondary mode only).

• Only one authentication configuration per username can be configured at any one time.

• A maximum of six registrars can be configured at any given time.

• A maximum of 12 different realms can be configured for each endpoint.

• You cannot restrict the registration of specific endpoints with specific registrars--once a new registrar is configured, all endpoints will begin registering to the new registrar.

• You cannot remove multiple configurations of credentials simultaneously--only one credential can be removed at a time.

For information about the Support for Multiple Registrars on SIP Trunks feature and for detailed procedures for enabling this feature, see the "Configuring Multiple Registrars on SIP Trunks" chapter of the Cisco IOS SIP Configuration Guide.