code: func newIAAddr(ia *dhcp6opts.IANA, ip net.IP, w dhcp6server.ResponseSender, r *dhcp6server.Request) error {
  	// Send IPv6 address with 60 second preferred lifetime,
  	// 90 second valid lifetime, no extra options
  	iaaddr, err := dhcp6opts.NewIAAddr(ip, 60*time.Second, 90*time.Second, nil)
  	if err != nil {
  		return err
  	}
  
  	// Add IAAddr inside IANA, add IANA to options
  	_ = ia.Options.Add(dhcp6.OptionIAAddr, iaaddr)
  	_ = w.Options().Add(dhcp6.OptionIANA, ia)
  
  	// Advertise address to soliciting clients
  	log.Printf("advertising IP: %s", ip)
  	_, err = w.Send(dhcp6.MessageTypeAdvertise)
  	return err
  }
docs: // newIAAddr creates a IAAddr for a IANA using the specified IPv6 address,
  // and advertises it to a client.