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I am trying to establish a TCP connection with a server. I added a firewall rule in the server to drop the TCP packets in order to check how the TCP client terminates.

Client retransmits SYN multiple times and will not receive SYN+ACK and finally the client terminates. I could only see SYN retransmissions in the tcpdump and there was no FIN or any indications on how it closed. So, does the client terminate silently without sending out any closure packet in this case?

And how many times a TCP SYN is retransmitted?

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  • Unfortunately, questions about hosts/servers are off-topic here. You could try to ask this question on Server Fault for a business network.
    – Ron Maupin ♦
    Jan 21 at 19:22

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... there was no FIN or any indications on how it closed

A FIN is used to signal to the peer that the connection gets closed. Since the connection was never established in the first place, no FIN is sent to close it.

And how many times a TCP SYN is retransmitted?

This depends on the system and its tuning. For example in Linux there is tcp_syn_retries:

tcp_syn_retries (integer; default: 6; since Linux 2.2)
The maximum number of times initial SYNs for an active TCP connection attempt will be retransmitted. This value should not be higher than 255. The default value is 6, which corresponds to retrying for up to approximately 127 seconds. Before Linux 3.7, the default value was 5, which (in conjunction with calculation based on other kernel parameters) corresponded to approximately 180 seconds.

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