Null response from GTM

Hi,

I'm trying to create GTM iRule that will respond with NX-DOMAIN when all pool members are down. I found the following example on devcentral but don't know what should be the replacement for cname line. Have tried drop and reject but they both don't send the response at all causing timeout on the client side. Would appreciate any suggestion.

when DNS_REQUEST {
  if { [active_members pool_name] == 0} {
   cname "test.com"
  }
}

Thanks.

Best regards,

-Boris