VNC and Zonealarm

Seb Wills saw27 "at"
Fri, 28 Sep 2001 16:14:00 +0000

I use VNC between two machines on a LAN (the client being a Win98
machine). Normally, VNC is highly responsive, and can do a full screen
refresh in less than a second.

If I enable ZoneAlarm (a free personal firewall which seems to be
generally fairly highly regarded) on the client machine, VNC becomes
unusably slow - it can barely keep up with moving the cursor around, and a
full refresh takes 10s of seconds.

Initially I assumed ZoneAlarm must just slow down all traffic a heck of a
lot. But if I FTP a 5Mb file between two local machines, ZoneAlarm makes
negligible difference to the transfer rate (433k/s instead of 466k/s).

Can anyone suggest why ZoneAlarm is particularly affecting VNC performance
and how to get round this (other than turning off ZoneAlarm when I use


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