Home > System Configurations > Configuring a 3CX Trunk

Configuring a 3CX Trunk


  • Details in this document are for reference only and are unsupported by the Flowroute support staff.
  • Please use as purely reference material; we make no guarantees that this information is correct, or will not harm your system. Please be careful and always keep a backup of anything before you make changes, or alter settings.

Step 1

  • Click on SIP Trunks
  • Click Add SIP Trunk
  • Select Generic from Country dropdown
  • Select Generic SIP Trunk from Provider dropdown
  • Input your Flowroute phone number in 11 digit format under Main Trunk Number (1NPANXXxxxx)
  • Click OK


Step 2

  • Enter an arbitrary name for the trunk
  • Enter your preferred PoP registration URL (such as us-west-wa.sip.flowroute.com)
You can select your preferred PoP by logging into your Flowroute account and going to Interconnection and then Registration. Once you select your preferred PoP, you will see the signaling URL as well as your username and SIP password on the right-hand side.
  • Set whatever maximum number of simultaneous calls you desire

Step 3

  • Under the Authentication section select Register/Account-based auth.
  • Enter your tech prefix as the username
  • Enter your SIP password for the Auth Password
You can locate your tech prefix and SIP password by logging into your Flowroute account and going to Interconnection and then Registration. 

Step 4

  • Click on the DIDs tab
  • Add any additional Flowroute DIDs you wish to receive calls on. Numbers should always be entered in the 11 digit format (1NPANXXxxxx)
  • If you plan to use some numbers for the built-in 3cx fax server or conferencing server, you will need to enter the numbers you intend to use for those services in full E.164 format. (+1NPANXXxxxx)

Step 5

  • Click on the Caller ID tab
  • Enter your preferred outbound caller ID in 11 digit format (1NPANXXxxxx)
If you need to reformat your inbound or outbound caller ID for any reason, please see this article from 3CX. https://www.3cx.com/docs/cid-reformatting/ If you have any questions related to this process, please contact 3CX or your PBX administrator.


Step 6

  • Click on the Options tab
  • Ensure allow inbound, and outbound calls are selected

  • Ensure that Supports Re-Invite is checked under Advanced

If your PBX is behind NAT, please ensure that the following options are set, and your Public IP is listed in the specified fields. If you are unsure if your PBX is behind NAT, please see your network administrator. If your ISP is providing dynamic IP, you will need to manually update these fields if your IP changes in the future. Failure to update the IP will result in no inbound audio on calls.
  • Put Public IP in SIP VIA Header
  • Select which IP to use in 'Contact' (SIP) and 'Connection'(SDP) fields
    • Use This IP Address

  • Click on the Inbound Parameters tab
  • Set the following fields
    • "CallerNum" caller's number (default: From->user) : P-Asserted Identity: User Part
    • "CalledNum" number that has been dialed (default: To->user) : Request Line URI: User Part
    • "CallerName" caller's name (default: From->display name) : P-Asserted Identity: Display Name