What is the behaviour of TCP if ACK is lost for ever. Will retransmission happen for ever or will the connection be reset ?

Lets say A is TCP-server and B is TCP-Client. If the Server, A, fails silently after a while without sending a FIN and without sending a reset, will the client TCP-stack retry indefinitely ? Or is there a timeout after which the connection will reset ?

Note: Assuming the server and client applications doesn't implement any TCP keepalive mechanisms.

2 Answers 2


TCP connection is closed after certain number of unsuccessfull retransmissions. I think this number is 5.

This however only happens if there is actually a packets (segment) to be sent and retransmitted. If there are no outgoing segments, and keepalives are not used, then the socket is opened forever.


In real world, there are timeouts on both modern transport layer and applications. Nothing is retried indefinitely these days.

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