Issue: Cisco TelePresence endpoint cannot make H323 point-to-point call to another Cisco TelePresence endpoint. Both endpoints are standalone H323 and no Gatekeeper. Symptom is when calling from either endpoint the call automatically get disconnected after few seconds.
Platform: EX, SX, MX and Integrator C series TelePresence endpoints
Software version: Any version as long it supports H323.
Findings: Checking for any system errors in the logs revealed the issue was caused by the H323 NAT was turned on. Note that H323 NAT is on by default.
Mar 1 15:43:03 (none) main: H323CC: Inc Setup, NAT enabled but H323 NAT address not configured, disconnecting call
To fix the issue, login to administration web page. Go to Configuration > Advanced Configuration > H323 > NAT > Then set the mode to off.