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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.

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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.

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

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