Siebel thick Client URL Issue - FQDN

Siebel thick Client URL Issue:

Whenever, we open siebel thick client(local) it takes URL automatically as

http://(machine name)/start.swe

but when we move from local network to Client network by using VPN or whenever we change port or IP. Siebel thick client disconnected and we get message 'Page not found' and need to restart thick client again.This can be avoided by using following two parameters of cfg file under section [Siebel]

EnableFQDN = TRUE
FQDN = localhost