iRule to extract XFF IP address in HTTP Packet

Take at look at the following code snippet XFF Universal Persistence iRule.

It is for persistence but you can change from persist to log or anything else you want to do with the XFF header data.

when HTTP_REQUEST {
   log local0.  "X-Forwarded-For: [HTTP::header X-Forwarded-For]"
}

There is an iRule to extract client IP address.

    when HTTP_REQUEST {
         HTTP::header insert X-Forwarded-For [IP::remote_addr]
          }

Go through f5 article K4816

Hope it will help you..