SIP server on a different SUBNET

[Quest4Voice]

Evening experts.

Below is my Challenge.

I have a WAN link that has been provided to me by the SIP service provider. I have been given a /30 IP. ie 192.168.70.2 ( My SIP server) and 192.168.70.1 my gateway on the provider end.
In my network i have a Mikrotik router with 10 ports. A server on which i have loaded the 3CX that has one Ethernet port also.

My challenge with 3CX:

1. The IP provided by the service provider will have to terminate on my Mikrotik gateway meaning I will have to give my 3CX another IP address. My Issue is other deployments with other vendors the SIP servers have a LAN and WAN. On the LAN I will put a subnet like 10.10.10.0/24 IP address range for phones. Whilst on the WAN 192.168.70.2 will be configured. With Other Vendors this works and solves this network challenge.

OUR CASE

1. I have one port on the server how then do i share this port between the WAN and LAN? If were to configure as other vendors do one leg would be on WAN the other on the LAN.
2. I have one IP address assigned to me from the SIP provider they expect to create a SIP trunk between 192.168.70.2 and their SIP peer IP address. How do create the trunk if my SIP server IP is on the Mikrotik and my 3CX server has a LAN IP in a different Subnet.
3. If I put the 3CX on the local LAN so that the phones register how then do i bring up the trunk remember the SIP IP address will be on the Mikrotik router not on the 3CX server? Is there some NAT to be configured?

How do i resolve this night mare am in. If there is need for a network Diagram i can draw one.

I await for you input and suggestions thanks in Advance.

 

[ChrisC_3CX]

To achieve this you'll definitely need two NICs on the 3CX PBX Host. If we're talking about a physical machine you might want to consider switching to a VM to make this even easier by utilizing two virtual interfaces.

One of the two NICs should then have a default gateway(192.168.70.1) and therefore used for all Internet traffic and the other should be used in conjunction with static routes so that you can have Voip traffic use that NIC only. That said, you should terminate the SIP IP on the 2nd (Voip) NIC instead of the mikrotik.

You might want to take a look at the last network configuration mentioned here (Multiple Internet Gateways): https://www.3cx.com/blog/docs/network-configurations-supported-3cx-phone-system/