X-Forwarded-For through proxy and F5

The below code will check for X-Forwarded-For header. If id does not exist it will grab the client address and insert X-Forwarded-For Header in the request.

i.e if proxy already inserted X-Forwarded-For no need to worry as it will have the client IP. If not coming through proxy, insert XFF header with the client IP. Will this help ? Bit modified from Soda's iRule.

when HTTP_REQUEST {     
        if {not ([HTTP::header exists "X-Forwarded-For"])} {
          set XFF [IP::remote_addr]
          HTTP::header insert "X-Forwarded-For" $XFF
        }
 }