code: func routeDefaultIPv4() (net.IP, error) {
  	out, err := ipRunAFOutput(seesaw.IPv4, "route show default")
  	if err != nil {
  		return nil, err
  	}
  	if dr := routeDefaultIPv4Regexp.FindStringSubmatch(out); dr != nil {
  		return net.ParseIP(dr[1]).To4(), nil
  	}
  	return nil, fmt.Errorf("Default route not found")
  }
docs: // routeDefaultIPv4 returns the default route for IPv4 traffic.