SIP Trunk Port Handling & SRV Record Behavior

Introduction

This document explains how Port configuration and DNS SRV resolution work when configuring a SIP Trunk.

SIP Trunk Ports

Port Field Rules

• Port is mandatory
• Valid range: 0 – 65535

Port Behavior Logic


Case 1: Port = 0 (SRV Mode)

• Proxy saved without port (e.g. callcentric.com)
• System performs DNS SRV lookup



Case 2: Port > 0


• Proxy saved with port (e.g. callcentric.com:5060)

• No SRV lookup

Loading Existing SIP Trunks


• If proxy has port → extract port

• If no port → default to 0

New SIP Trunk


• Default port = 0 if not provided

DNS SRV Explanation


• Query example: _sip._udp.domain.com

• Returns target server, port, priority

Fallback


• If no SRV found → fallback to port 5060

Best Practice


• Use Port = 0 unless provider requires fixed port