Ascend Archive
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Re: (ASCEND) Pool handling strategies (was: IP Addresses needed for 4048)
Keepalives were invented by application writers who decided they did not
like the way TCP connections worked and figured that they knew better than
the original designers.
At 03:58 PM 4/1/98 -0500, Phillip Vandry wrote:
>> No. Host Unreachable is a temporary condition which could be repaired at
>> any time. It just means there's a break in the path to the host at the
>> moment. Remember that TCP is intended to survive nuclear war and in such an
>> event it's not unreasonable that there might be temporary outages in the
>> network. :-) Host Unreachable is a valid reason to fail at opening a
>> connection, but it's not a valid reason to close an established one.
>> Session close should only be done by end to end agreement (or disagreement
>> e.g. if one party had rebooted and lost the connection state).
>
>One last question, and then we'll call this off topic :-)
>
>But then are are TCP keepalives for? Aren't they used to detect failed
>connections and close them?
>
>> I'm told that in the early days of TCP development at BBN a telnet session
>> happened to be left open between two machines when some piece of the
>> network between them was taken down for other experiments. A month later
>> when the two hosts were again connected by a working network the telnet
>> session was still alive.
>
>Good anecdote!
>
>In my experience this works UNLESS one of the sides tries to send data
>to the other side. If that happens then it will usually time out and close
>itself within a few hours. Maybe that's newer stuff that wasn't around in
>the BBN day?
>
>-Phil
>
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