redirect wwwX.domain.com to www.domain.com

Here's something that might work for you. I'm not sure what you want to do if the client either doesn't set a host header value or uses an IP address, so I've just left a comment in the default switch case.

when HTTP_REQUEST {

    Check requested host set to lowercase
   switch -glob [string tolower [HTTP::host]] {
      "www.*" {
          Host starts with www. so exit this event in this iRule
 return
      }
      "*[a-z]*" {
          Host isn't an IP and didn't start with www., so send permanent redirect
         HTTP::respond 301 Location "http://www.[domain [HTTP::host] 2][HTTP::uri]"
      }
      default {
          Host is either blank or an IP address, do something?
      }
   }
}

Aaron