How to configure multiple SIP Registrar

I want to configure the FreeSBC to register multiple SIP registrar for 1 domain. I see there is an option to create SIP Registrar in the same domain. What's the maximum number of SIP registrar supported? How would the SIP register message passthrough to these Registrar (round robin? send to all?)

Hi Bronze,

At the moment, we are supporting Active/Standby mode of Registrar redundancy, meaning the active and the priority Registrar will take the registration request first. If active fails, standby one will take over. Although, we tested more than 2 Registrars, you could stick with 2 Registrars for normal use.

Best regards,
William

Thank you William! That's very helpful! 2 registrar with active/standby is good enough for deployment.

Additional questions about the multiple SIP registrar

During switchover, what would be the expected behavior for existing calls and registered users?
- Shall we expect the users will be registered to the secondary Registrar automatically?
- Would existing calls remain connected or dropped?
- Apart from the SIP registrar configuraiton, what would be the necessary routes in the routing table to make sure the service continue after the switchover?

Please check our answers below;

- Shall we expect the users will be registered to the secondary Registrar automatically?
 
If SBC has a problem communicating with the primary registrar, SBC will send new incoming registration messages automatically to
  secondary registrar. In normal conditions, users IPPHones send registration renewing at certain intervals that new registration will go to secondary registrar.

- Would existing calls remain connected or dropped?

Existing calls will be dropped.

- Apart from the SIP registrar configuration, what would be the necessary routes in the routing table to make sure the service continues after the switchover?

2 different routes must be created for the primary and secondary servers. As explained in the following link;
https://docs.telcobridges.com/tbwiki/FreeSBC:Hosted_PBX:Configuration_A#Call_Route