On 24-May-06 Ewan Leith wrote:
Telnet (and tcp applications in general) sends a keepalive pack every 75 seconds, if you had been lucky enough to resync without clashing with one of these 75 second intervals, your link would have continued.
more specifically, i think the message your telnet client sends to the server is "ack 31" and it expects in reply "ack 4". if the server doesn't receive an ack 31 within it's window, it will end the connection, and the client will end the link without an ack 4 in response.
if you're using a UDP application instead of TCP, it'll implement its own similar keepalive system independantly of any other applications.
if you regularly have these problems, you can look into a gpl application called screen - you use it as part of your login session setup and it will let you run multiple telnet sessions over one link, and more usefully for you, reconnect to a session which had been lost
Ewan
Thanks, Ewan, that makes sense! (And shows that I did manage to explain my question). And the tip about 'screen' looks useful (I used to use screen quite a lot in the old SLIP days, between machines connected with a serial cable, but I haven't touched it for years now).
But your comment raises another question: If the hiatus in the "ACK 31"/"ACK 4" exchange causes the link to be ended by one side or the other as you explain, how can 'screen' reconnect to it?
Thanks again! Ted.
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