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
