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How to Configure 3CX in IP-to-IP Mode (No Registration Required)

This guide explains how to set up 3CX to connect directly with another SIP system (such as a gateway, another PBX, or SBC) using IP-based routing without authentication. This is often referred to as an IP-to-IP or peer-to-peer SIP trunk.

Step 1: Create a Generic SIP Trunk

  1. Log in to the 3CX Management Console
  2. Go to SIP Trunks → Add SIP Trunk
  3. Set the following options:
    • Country: Generic
    • Provider: Generic SIP Trunk
    • Main Trunk Number: Enter a dummy number (e.g., 10000)
  5. Click OK

Step 2: Configure the Trunk Settings

General Tab

  • Registrar/Server/Gateway Hostname or IP:
    Enter the public or private IP address of the remote SIP device (e.g., another PBX or gateway)
  • Outbound Proxy: Leave blank (unless needed)
  • Authentication Type:
    Select Do not require - IP Based
  • Number of Channels: Set the number of allowed concurrent calls (e.g., 10)

DIDs Tab

  • Optionally add any DID numbers (if used in routing logic)

Inbound Parameters Tab

  • Make sure the SIP Field containing DID is set to:
    Request Line URI: User Part — This is typical for IP-based peer trunks

Outbound Parameters Tab

  • Optionally configure the From: Display Name and From: User Part to control caller ID presentation

Step 3: Configure Inbound and Outbound Rules

Inbound Rules

  1. Go to Inbound Rules
  2. Click Add DID Rule
  3. Set the destination for incoming calls — for example, an extension, ring group, or digital receptionist

Outbound Rules

  1. Go to Outbound Rules
  2. Click Add
  3. Define a dialing pattern (e.g., X. to match all numbers)
  4. Select the SIP trunk created earlier as the route

🔒 Firewall and IP Trust Settings

  • Ensure that the remote IP address is allowed in 3CX:
    • Go to Settings → Security → IP Blacklist → Add
    • Add the IP of the remote SIP system and mark it as trusted
  • If NAT is used, make sure that SIP and RTP ports are properly forwarded
  • Both sides must accept calls without registration or authentication

✅ Example Use Cases

  • Direct interconnection between two PBX systems
  • SIP trunk between 3CX and a VoIP gateway
  • Secure SIP trunking in closed environments (e.g., LAN or VPN)

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