How to setup Dual Mode for Private SIP Trunk on UCM 6104


Have a perfectly fine running setup with 4 analog trunks. All remote extensions can connect to the PBX and everything works fine. Network is set to Switch Mode where LAN 1 of PBX is connected to a router ( Subnet) with internet uplink.

Now we have got a new Multiline SIP connection from the same ISP. The problem is they have brought in a separate fiber line for this terminated to a ONU , which is further connected to a Tplink router (i think for bridging the VLAN on port 3) as the ISP asked us to connect the IP PBX to LAN 3 of this router.

My question is would it be possible to connect this SIP trunk along with my existing Internet connection using DUAL mode (LAN 1 to existing internet connection & LAN 2 to the new Multi Line SIP connection) and would my remote extensions work in this setup…how should i go about it

Any help will be highly appreciated…


I think yes, but i remember problem on older soft with this.
Also you need make STATIC routing for correct working.


Yes it’s possible, but you may need to bring the remote phones in on the fiber side

Careful of loops.


Hi Istutesman, Many thanks for your reply. The problem is the SIP trunk they have provided is on a private network and they dont provide internet connectivity on this one. For internet services we have another connection


Can you provide more information on this one?

If they are bringing the Trunk in on their own device like an adtran, then you make your own private network between the WAN port and this device and trunk them together.


Any updates? I have the same issue with AT&T IP-Flex BVoIP. It is a private, separate lan connection and no authentication. I have setup a static route using the static IP of LAN2, but the connection still tries to go out on internet LAN1. I never see lines available in the trunk.


How does the IP of the ATT device differ from that of your normal LAN? Normally, you can get ATT to change the IP to one on your LAN so that it looks like nothing more than another device on the LAN and then you can use switch mode on the UCM.


Dual mode
WAN side goes to SBC
LAN side goes to network and internet connection
Gateway is set to the LAN side


It’s very simple. In dual mode, one port (LAN1) goes to your switch/network/internet and the other port (LAN2) to the SIP provider.
Make sure to configure your LAN2 port with static IPs as provided by the provider, under network settings.
You will then create static routes, use the signalling IP as the destination network, subnet you can leave blank but i use and it works fine. Gateway is the next hop private IP of the provider, same as what you put as your gateway when configuring LAN2 network settings. Exit intf in LAN 2.
If you have created the VoIP trunk, it should be reachable by now


I am having to do a similar setup,
can you elaborate a bit more on the solution,
specially on the static route setup.
am not sure what the signalling ip is (would it be our SBC device?),
and the route destination (gateway) ip I am assuming is the our SBC device in my case?



Only the Network side will have a gateway.
SBC will just be static IPs


Hope you were able to get this solved.
From where i come from, the signalling IP, is the DNS IP that the provider will give. It is what will go to the IP field when creating the Peer SIP trunk (your new VoIP trunk)