How to find packet type

Question

I am implementing a vpn client in android using toyvpn sample. I want check details of packets send and receive by tunnel. I am using jpcap library to read packets but I'm not really know packets are in what protocol. my question is how to find type of packets.

        // Packets to be sent are queued in this input stream.
        FileInputStream in = new FileInputStream(mInterface.getFileDescriptor());

        // Packets received need to be written to this output stream.
        FileOutputStream out = new FileOutputStream(mInterface.getFileDescriptor());

        // Allocate the buffer for a single packet.
        ByteBuffer packet = ByteBuffer.allocate(32767);
        // Read the outgoing packet from the input stream.
        int length = in.read(packet.array());
        if (length > 0) {
                // Write the outgoing packet to the tunnel.
                packet.limit(length);
                tunnel.write(packet);

                // i use ip packet of jpcap but i think it is wrong
                IPPacket ipPacket = new IPPacket(length,packet.array());
        }

Answer 1

Ok I found answer. any packet received in vpn tunnel is internet layer packet. in this case we receive ip packets and then we can extract tcp or udp packet from that.