SIP Dedicated Trunk Application for S-Series VoIP PBX


In some cases, client might have a dedicated SIP trunk from the provider. This kind of SIP trunk usually offers a dedicated cable to be connected with which comes from a specific ISP router, and exclusive for voice only without Internet access function. So what's the plan?

Regarding to S-Series VoIP PBX, there are 3 points noted:

  • Network interface should be configured as Dual Mode: One is for the SIP dedicated trunk. The other one is for local network and Internet access
  • Static Routes and Default Network Interface should be configured well. The SIP dedicated trunk data goes through the interface that it connects, and the rest data goes through the other interface.
  • If SIP remote extension solution is involved, the NAT settings should be taken into consideration. This is to avoid one-way problem.


Network Information Gathering

Here we have a sample for dummy use.

Local network IP address:, Gateway:
SIP Trunk SIP trunk IP address & port:; Interface IP address: 110.87.*.*, Gateway IP address:
Public IP IP address: 120.41.*.*


  • The Local network depends on your own planning. It is the local network that the PBX is deployed.
  • SIP Trunk IP address information was offered by the SIP trunk provider. Usually includes the interface IP address & gateway IP address, SIP trunk IP address & port.
  • Public IP is the public IP address that the remote extension registers to.

Simple Topology


Settings on the web interface

1. Network Settings


2. Add Static Route for the SIP trunk


Route table review


3. If remote extension solution is involved, please proceed.



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  • 0

    Try this configuration but defenately not working for me. So the scenario is like this. I have 3 SIP Trunk Account.

    A is from my telecom provider (with private sip trunk)
    B from skype
    C from some other company

    So provider give me a Huawei HG8245H ONT router which configured with 2 WAN Connection. So one for the internet and one for the private sip trunk account. The sip trunk account can only be use by connecting to ethernet port number 2. So ethernet number 1, 3 and 4 is free for internet.

    I have the following WAN information from my router.

    SIP TRUNK: / 5060 (UDP)


    NAT: Enable
    IP Acquisition Mode: DHCP
    IP Address/Subnet Mask:
    DNS Servers:


    NAT: Enable
    IP Acquisition Mode: PPPoE
    IP Address/Subnet Mask:
    DNS Servers:,

    I try the above configuration but defenately not working for me. In the NAT Setting under PBX > General > SIP, I try to configured with EXTERNAL IP ADDRESS and EXTERNAL HOST since I'm using DDNS services, but both of them is not working.

    Now, I have also try this.

    In my Huawei HG8245H ONT router, there is a feature where I can setup a secondary IP address. So now I have 2 set of IP address with different class on my router.

    LAN (The LAN port connect to a Hub which is also connect to the router) /

    WAN (The WAN port is connect to the router ethernet port number 2 which is private for the sip trunk) /
    Gateway: Empty

    In the static route, I have try the following but none of them work.

    Gateway: Empty
    Interface: WAN

    Gateway: Empty
    Interface: WAN

    As for the NAT setting in PBX > General > SIP, I configured as follow.

    NAT Type: External Host
    External Host:
    Refresh Interval: 120s
    Local Network Ideentification: /
    Local Network Ideentification: /
    NAT Mode: Yes

    And with this configuration, I can succesfully access the B and C SIP trunk account. But not the A which coming from my telecom company.

    Any advice?

  • 0

    We've set up both configuration with the Yeastar S-Series.  For the most part, using the single network configuration and rely solely on the LAN interface is the simplest.  

    We recently deployed a S100 on a site that had a Sophos firewall and the Sophos was not co-operating with consistently passing SIP traffic.  As a fix we decided to leave the Sophos in place but get a second static IP from the ISP to dedicate to the WAN port of the S100.  This has worked much better.   The Sophos remains the default gateway/firewall for the network.   We needed to set the default adapter in the S100 to be the WAN port to ensure the traffic routed properly.  We also changed the SIP settings in the S100 to reference the dedicated static IP.

    I've created a YouTube video about connecting a SIP trunk to the Yeastar S-Series Phone System.  I hope it will be of some help. It can be found at:

  • 0
    Local network IP address:, Gateway:  (LAN)
    SIP Trunk

    SIP trunk IP address & port: ,; Interface IP address:, Gateway IP address:  (WAN) 

    wan is no internet access 

    lan is internet access 

    how to route

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