The TCP connection drops after quickly unplugging and replugging the Ethernet cable

Question

The TCP connection drops after quickly unplugging and replugging the Ethernet cable

YS P 0

My PC is running Windows 10, acting as a TCP client that communicates with a controller functioning as the TCP server. After I quickly unplugged and reconnected the Ethernet cable, the TCP connection was already disconnected, and the system could no longer find this connection entry.

Packet capture results show that after the cable was reconnected, the controller sent data packets to the PC, but the PC responded with an RST (reset) packet.

Why does unplugging and replugging the network cable cause the TCP connection to drop? What methods can be used to keep the TCP connection persistently connected?

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Answer 1

Tracy Le 13,690 Independent Advisor

Hello YS P,

What you are seeing is expected TCP behavior. When the Ethernet link is unplugged, Windows detects a physical link loss and the existing TCP session becomes invalid. After the cable is reconnected, the controller may still believe the session exists and continue sending data, but the Windows TCP stack no longer has a matching connection state, so it responds with a TCP RST packet.

In practice, there is no supported way to guarantee that a TCP session survives an actual link-down event caused by unplugging the network cable. The recommended approach is for the client application to detect the disconnection and automatically establish a new TCP connection when network connectivity returns.

If reconnection needs to happen quickly, consider implementing TCP keepalives, application-level heartbeats, or automatic reconnect logic in the client software. Those mechanisms are typically used in industrial control and telemetry applications where temporary network interruptions are expected.

If this helps, please accept the answer.

Tracy Le.

YS P 0 Reputation points

2026-10-14T01:11:45.1533333+00:00

By definition on a layered model as OSI or TCP/IP each layer works independent and not-aware of the lower layers.It doesn't make sense that a short-term physical link loss would cause the TCP connection to drop, right? I found another Windows10 where the TCP connection remains established even after unplugging and replugging the Ethernet cable. However, I couldn't identify any differences in the TCP configuration between the two systems. I want to know what causes this discrepancy.