History:

I am using ethtool to change the link rate of my NIC between 10Mb/s and
100Mb/s and everything works fine. When timing the delay for the change
on my switch there was a 1 second delay between the 10Mb and 100Mb
lights changing. However when timing downloads and verified with
ethereal/wireshark traces the actual delay is 4-6 seconds. I
originally thought this was an ethtool problem (either reseting the NIC
or reloading the driver, etc).

Current:

To determine if it was ethtool or not I repeated the same download but
this time physically unplugged the server from the switch for 1 second
(to simulate the 1 second light change delay noted above). I observed
the same delay of 4-6 seconds in the timing and ethereal/wireshark
traces. This leads me to believe it is not a ethtool issue but a TCP
issue in reestablishing the connection.

I think it is TCP because although the TCP packets took over 4 seconds
to show back up in the trace other protocols are logged by
ethereal/wireshark just fine. Spanning Tree, ARPs, CGMP, CUPS, etc..

Information:
-The connection is not broken. There is no SYN, SYN-ACK, ACK after the
interruption.
-Same port on the client is used before and after the interruption.
-There is another delay of the exact same type/description 4-5 seconds
after the TCP connection is re-established. Almost as if I did the
unplug/ethtool event twice. But I didnt.

Does anyone know what the cause of this delay is? I have not had any
luck finding this information.

Thank you,

-Matt

One possibly related bit...

Each time TCP had to retransmit, the timeout for the next
retransmission of that same segment (packet) was doubled. So, if the
link is down for a little over a second or so, it could have had its
RTO back-off enough to get close to 4 or more seconds. Depends in
part on what the initial RTO was relative to the actual length of the
link's "downness."

rick jones
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