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Editorial Team
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Asked: 2026-05-31T13:12:14+00:00

I have a C++ application which accepts TCP connections and then reads the traffic

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I have a C++ application which accepts TCP connections and then reads the traffic sent to it. It has worked very well until I moved it to a new machine. It seems like winsock never accepts the inbound tcp connection. In my code it never returns from the select statement. I can see using netstat/tcpview that the application is listening on port 14005.

I can connect to this port if I just telnet in locally. However, when someone tries to connect in via an outside IP address the TCP 3 way handshake never finishes. I can see the inbound SYN packet in wireshark. It is going to the correct port, 14005. However my system never sends the SYN-ACK back. This is just something that winsock is suppose to handle right? The machine does have multiple NIC cards, but I’m binding with INADDR_ANY so this shouldn’t matter. Is there some way I can dig deeper to see why this handshake never takes place?

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1 Answer

  1. Editorial Team

    per ways to dig deeper: nothing more than wireshark / tshark (which you already use, however if you want to play with packets, look at scapy)

    what happens if you reduce headache – only use one nic and network, put the client on the same network (ie, no router or smart switch between), (last resort) disable unneeded network services.

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