Answer by Jaap for I'm trying to build a transparent proxy in Java with the ability to record data that passed through to be viewed later in wireshark.I was able to get the proxy working correctly with this snippet private static final int BUFFER_SIZE = 8192; ... public void run() { PcapHandle handle = null; PcapDumper dumper; try { InetAddress addr = InetAddress.getByName("localhost"); PcapNetworkInterface nif = Pcaps.getDevByAddress(addr); int snapLen = 65536; PcapNetworkInterface.PromiscuousMode mode = PcapNetworkInterface.PromiscuousMode.PROMISCUOUS; int timeout = 10; handle = nif.openLive(snapLen, mode, timeout); dumper = handle.dumpOpen("cap.pcap"); byte[] buffer = new byte[BUFFER_SIZE]; try { while (true) { int bytesRead = mInputStream.read(buffer); if (bytesRead == -1) break; // End of stream is reached --> exit mOutputStream.write(buffer, 0, bytesRead); dumper.dumpRaw(Arrays.copyOfRange(buffer, 0, bytesRead)); mOutputStream.flush(); } } catch (IOException e) { // Read/write failed --> connection is broken } dumper.close(); } catch (PcapNativeException e) { e.printStackTrace(); } catch (UnknownHostException e) { e.printStackTrace(); } catch (NotOpenException e) { e.printStackTrace(); } } As you may notice I'm using Pcap4J to store raw bytes into a pcap file. The saving of the bytes works well but when I try to open it on wireshark it shows this message:ErrorAnd every packet shows as malformed. Ideally I would be seeing TCP and CQL (Cassandra) packets.Can anyone tell me what I'm doing wrong here?

You are reading raw packet data through the use of Pcap4J, but are not writing [PCAP](https://wiki.wireshark.org/Development/LibpcapFileFormat) format files. You simply dump the raw packet data into a file. You need to add the file format structures are well.