ImmutableSet.Builder<String> builder = ImmutableSet.builder();
    Enumeration<NetworkInterface> interfaces = NetworkInterface.getNetworkInterfaces();
    assertTrue(interfaces.hasMoreElements());
    while (interfaces.hasMoreElements()) {
      NetworkInterface i = interfaces.nextElement();
      builder.add(i.getName()).add(String.valueOf(i.getIndex()));
    }
    return builder.build();

      if (interfaceIndex != -1) {
        return Inet6Address.getByAddress(
            v6Address.getHostAddress(), v6Address.getAddress(), interfaceIndex);
      }
      try {
        NetworkInterface asInterface = NetworkInterface.getByName(scope);
        if (asInterface == null) {
          throw formatIllegalArgumentException("No such interface: '%s'", scope);
        }
        return Inet6Address.getByAddress(