code: func IsLAN(ip net.IP) bool {
  	if ip.IsLoopback() {
  		return true
  	}
  	if v4 := ip.To4(); v4 != nil {
  		return lan4.Contains(v4)
  	}
  	return lan6.Contains(ip)
  }
docs: // IsLAN reports whether an IP is a local network address.