My client and server are both internal machines. tcpdump on both client and server show all three parts of handshake are communicated, however netstat on server shows SYN_RECV, and on client shows ESTABLISHED. The server keeps sending a syn-ack as though it never received the client's ack.

Below is a link showing:

  • Server tcpdump (jbod-bubbles)
  • Server netstat showing SYN_RECV
  • Client tcpdump (mrnobody)
  • Client netstat showing ESTABLISHED


  • Interesting, do you have iptables running ? Did you make sure none of the IPs are mounted twice and that there's no duplicate mac address ? – Xavier Lucas Nov 4 '14 at 19:49
  • 2
    Misconfigured firewall on server (only allowing syn but not other packets) – Dan Feb 1 '15 at 14:40

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