I often need to move my laptop around the house and have temporary network outages (no wireless). I've noticed that any active TCP connections drop out fairly quickly - some checking with tcpdump shows that there is only 60 seconds between the first transmit attempt and the last re-transmit. This strikes me as excessively short - it's likely to take more time than this for a managed switch or router to reboot.
I've previously (5-6 years ago) done some testing on other commercial Unices and got figures of 8-10 minutes - which seems more reasonable. Having had a look at the code, there are TCP_MAXRXTSHIFT (12) re-transmit attempts with exponential back-off based on the calculated RTT. Whilst this is probably reasonable for a WAN link, I would like to extend the timeout on LAN links. Can anyone see any downsides to either increasing TCP_MAXRXTSHIFT (and associated timer arrays) or changing retransmit timeout to having a minimum value (similar but opposite to the tcp_maxpersistidle test in tcp_timer_persist)? -- Peter Jeremy
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