var (
		err        error
		host, port string
		portnum    int
	)
	switch net {
	case "tcp", "tcp4", "tcp6", "udp", "udp4", "udp6":
		if addr != "" {
			if host, port, err = SplitHostPort(addr); err != nil {
				return nil, err
			}
			if portnum, err = r.LookupPort(ctx, net, port); err != nil {
				return nil, err
			}
		}
	case "ip", "ip4", "ip6":