const val MAX_RESPONSE_SIZE = 64 * 1024

    private fun buildBootstrapClient(builder: Builder): Dns {
      val hosts = builder.bootstrapDnsHosts

      return if (hosts != null) {
        BootstrapDns(builder.url!!.host, hosts)
      } else {
        builder.systemDns
      }
    }

    internal fun isPrivateHost(host: String): Boolean {