The story :
I have successfully installed an e-smith server and gateway
on a spare machine : that was very easy

Few weeks later, I receive a severe warning from my ISP
telling me that the upload traffic of my cable modem
connection was very very high, that I was among the 10% customers that use 90% of the bandwidth, and that I may
be charged for this etc. etc.
I installed netwatch.0.9g (found in sunsite.unc.edu/pub/linux/system/network/monitor)
and watch a ftp dowload :
1) when the ftp is issued from a machine inside the local net
every incoming packet seems to generate an outgoing packet
2) when the ftp is issued from the e-smith server the upload
traffic is normal (1% of the download traffic)
I don't understand ...
Any help will be appreciated.