21143 updates, and Re: large number of TX packets on ftp

[Peter Stein]

>> ifconfig is reporting no errors or overruns on ftp of a large file (67 Meg),
>> but is showing a large number of TX packets. The number always hovers around 
>> 38% of RX, so for 49000 RX packets ifconfig reports about 18000 TX packets.
>> 
>> What's going on? Am I not taking into account how the ftp implementation works
>> or is there something seriously wrong here? Shouldn't the receiving end of a
>> ftp session only attempt to send something if a problem occurs?

>It's normal.
>TCP streams work by acknowledging the received data and telling the sender
>"you can send this much more".  This happens about every other packet, with
>ACKs occuring more often if you get out of order data.

I actually pulled out the Stevens books (I haven't looked at TCP/IP innards
in a long time) and verified this. Sorry to have bothered you with this
question before checking.

It appears that on my small network the slow machine is a bottleneck for
everything. Doing the same ftp from the slow machine to the fast is more
than twice as fast! The numbers still aren't very good, but are probably
affected by the rate at which the slow machine can make the data available.
For this direction the TX packets are only 12% of RX as opposed to 38% in
the other direction. This seems pretty conclusive that the slow machine is
having trouble keeping up.

I still have some doubts about the driver performance the above conclusion
notwithstanding. Some additional experiments might be useful, like taking
disk I/O out of the equation (it appears /dev/null is not diskless). 

Peter Stein
nbi@xnet.com