Using Multiple iRule s for Client Selection

Since it's specific to the internal pool, why not just combine the logic:

when HTTP_REQUEST {
   switch [string tolower [HTTP::host]] {
      out.abc.com { pool out_abc_com }
      out2.abc.com { pool out2_abc_com }
      out3.abc.com { pool out3_abc_com  }
      internal.abc.com {
         if { [class match [IP::client_addr] equals allowedAddresses] } {
            pool internal_abc_com
         } else {
            discard
         } 
  }
      default { pool default_i2cinc_com}
   }
}

By the way, assuming you're not still on a 9.x box, matchclass is now deprecated and you don't need the "$::" syntax to address data groups.