Aside from disabling the SIP Helper in the Mikrotik, running multiple (eg 4) SIP Handsets (just doing NAT across a PPoE session) should have no issues?
The setup is a customer with four Polycom handsets to a third-party VoIP provider and the first three handsets to register have no issues, but the fourth handset fails. Reboot the router (or all handsets) and the first three always register fine, and the fourth one always fails to register.
Sorry if this is an old post, I am having the same issue with CCR1036 on 6.27 with Cisco devices. I can only register 1, and even sometimes that does not work.
I have tried with sip helper enabled and disabled with no difference.
In general, I’ve found the most problems happen whenever you try to make NAT pinholes on port 5060, 5061, etc.
If the provider’s server is able to work around NAT then you should be able to just use standard NAT without any special pinholes, port mappings, etc. The provider’s server should note and use whatever src port the NAT finds for mapping the additional phones. (since 5060 is taken by the first phone to register)
If you want, you can try hard-setting the second phone to using 5061, the third to use 5062, etc. as their local ports, but still register to the server on port 5060. That can help if you have stubborn phones / sip provider.