Check NAT and firewall boundaries before a voice change
Write down whether phones use a hosted system or an on-site PBX, every local NAT device, and the provider’s documented signalling and media requirements.
NAT and firewall boundaries before a voice change
- Save current firewall rules and NAT mappings. Check whether SIP ALG is enabled, but do not change it without confirming provider guidance.
- Plan inbound, outbound and two-way-audio tests on a known endpoint. Identify the person who can restore the old rules and the time allowed for session expiry.
A broad inbound rule is not an acceptable shortcut for a missing port map. Keep source and destination scope as narrow as the provider permits.
Check the wider path
Name the traffic direction for every proposed rule. Provider documentation may require different source restrictions for signalling and media, and some hosted services establish sessions outbound. Confirm the actual arrangement before exposing an inbound port.
Use the NAT and firewall troubleshooting for VoIP to confirm terms and settings before the change.