Proxy PAC files (redundent Proxy servers?)

Hi ok so i can set up a pac file to choses proxies based on network the Client is on and what site i am trying to get to.

but how do i set it up to sence if a proxy server is down and to use a secondery one??

is there any way to check if a proxy server is down completly (no ping) or is its still alvive (pinging) but not actauly responding to client requests and then set a different proxy?

Thank you

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Aaron StreetInfrastructure ManagerAsked:
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Check the PAC guide from Netscape:

You can specify multiple servers in the PROXY return variable and your browser should iterate through each one in order until it finds one that is up.

In other words, if your return is 'PROXY a; b; c; DIRECT', the browser will first use proxy server 'a', and if it is unable to connect then it will switch to using 'b', then 'c', then a direct connection.

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