Fortinet 377 FortiWeb 5.0 Patch 6 Administration Guide
When the external DNS name www.example.com appears in the client’s request’s HTTP Host:
header, it should be rewritten to www-internal.example.com.
In the server’s response traffic, when the internal DNS name www-internal.example.com
appears in the Location: header, or in hyperlinks in the document body, it must be rewritten.