This implies that the only thing to do is actually to run the DHCP server.
Automatic configuration of scopes By default, the DHCP server works in the mode of automatic configuration of scopes.
In general Kerio Control is known to work correctly and can be used as a gateway in front of a 3CX Phone System to connect Vo IP Providers, Direct Remote Extensions (STUN) and 3CX Tunnel connections.
However the Firewall features SIP and HTTP inspection where the functionality could not be determined.
For details, see above, section Automatic configuration of scopes.
NOTE You can use Add Use Interface Template, where parameters are already predefined in accordance with the particular firewall's interface.
The initial inbound stream causes the firewall to block data from and to the 3CX Phone System media server (RTP ip:port) for all connections, not even allowing the internal phones to send data to the 3CX Phone System.
Therefore, NAT rules must be configured for each IP Phone. The DHCP server assigns clients IP addresses within a predefined scope for a certain period (lease time).
Reservations can be set in both scope configuration modes, manual and automatic.
NOTE If possible, define the scope larger than it would be defined for the real number of users within the subnet.
NOTE DHCP protocol enables adding several optional parameters, such as: 015: Domain name — local Internet domain (not to be used for specification of Windows NT domain name).
This is mainly due to the behavior of the firewall expecting audio/data to be send before it allows receiving on dynamically created NATs.
Based on the timing, it could happen that the 3CX Phone System sends audio to the remote IP Phone’s IP: RTPport address, before the STUNed IP Phone has send data to the 3CX Phone System.
These addresses will not be assigned by the DHCP server.