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rsync opening and closing local ports


I am noticing that when I rsync data between two machines I see a constant stream of ports, at least 20 per second, being opened and closed on localhost.

I'm using the following rsync command:

rsync --blocking-io --compress --verbose --recursive --partial --times --rsh=ssh mylargefile

I see the localhost ports being opened and closed both via "netstat -an" and via my firewall (Agnitum Outpost).

This seems to be very inefficient and certainly causes problems with ZoneAlarm Pro firewall and possibly some with the logging subsystems of other firewalls.

Obviously it's not rsync's fault if the firewall has problems coping with high traffic loads, however in this case it does seem that rsync is causing an unnecessarily high load opening and closing ports to localhost.

I tried to capture the localhost connections in Commview but failed to get it to recognise any localhost connections - perhaps that's due to my lack of knowledge of Commview, and there doesn't appear to be a cygwin tcpdump. I was planning on trying Ethereal at some point but don't currently have it installed.

Enough rambling. Sorry.

Has anyone witnessed the localhost port opens/closes that I'm mentioning?
Can anyone explain what rsync is doing?


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