• Devices can’t register
• One-way or no audio
• Call drops or failed initiations

• Ensure devices can ping FreePBX
• Verify FreePBX has correct IP, gateway, DNS
• Open ports on firewall:
  • UDP 5060 or 5300(PJSIP)
  • UDP 5160 (Chan_SIP) 5060 on older systems
  • UDP 10000–20000 (RTP)
• Port forwarding enabled on router if behind NAT
• Disable SIP ALG on router/firewall

ping traceroute nmap -sU -p 5060