Hi Yi,
You should use the FQDN to access any SAP-based web service, including WEBGUI (or Personas).
The FQDN should be set in icm/full_host_name.
For some web applications the IP address is not supported (e.g. Web Dynpro ABAP applications).
Try testing the access directly to the server, not having any network device (reverse proxy, for example) between the server and the web browser.
Kind regards,
Cris