upstream proxy server not available

[nfigaro]

Hi All,

I have regularly such messages in the event viewer :

The Web Proxy filter detected that the upstream proxy server 'xxx.xxx.xxx.xxx' is not available.

then less than 1 sec after :
The Web Proxy service detected that the upstream proxy server 'xxx.xxx.xxx.xxx' is now available.

but sometimes, there is more than 1 minute between the first and second message.

During this period, I can still ping the upstream proxy,
and another ISA server doesn't have any trouble to reach the same upstream proxy.

has anyone ever seen this behaviour ?

what are the workaround ?

could anyone explain how the connectivity to the upstream server is tested ?

thanks