GTM iRule to set different TTL for each RR

Hi, ok thanks for the answer.

But what is the iRule function to be used for specifying the results coming from the RTT.

Can somebody help me to write something like that?

when DNS_response {

if {the result from RTT method is there}

  ttl = 60
  else
  {
  answer with DC_first
  ttl == 30
  }
  if (all DCs not available)
  {
  return DC_random
  ttl = 20
  }

}