IP to FQDN

Okay, so the iRule is looking for a request which contains the host header of 1.1.1.1. If the VIP is 2.2.2.2, then you can change the rule to check for 2.2.2.2. Or if you just want to rewrite the host header for all requests, you can remove the if check:

 
 when HTTP_REQUEST { 
     Replace the host header with www.example.com 
    HTTP::header replace Host "www.example.com" 
 } 
 

Aaron