iRule for URL rewriting

Maybe something like this:

when HTTP_REQUEST {
   set val1 [getfield [HTTP::uri] "/" 1]
   set val2 [getfield [HTTP::uri] "/" 2]
   set my_location "$val1.internalurl.com/$val2"
   HTTP::Respond 301 Location "$my_location"
   log local0. "Redirecting to $my_location"
}

Cheers.