PAC file hosting

[essam1982]

Hi experts,

how efficient is using DNS A record with multiple IP addresses (DNS round robin) for hosting PAC files?

I understand that the user machine will cache the DNS, however will it cache all IP addresses returned and try them one by one till one responds, or will it just try the last IP address used before?

I am considering hosting the PAC file on two S370 appliances, and use common DNS name for both of them to locate the PAC file for the client machines if suitable. any better alternatives?

thank you.

[essam1982]

By the way, this is meant for PAC file hosting high availability, in case one of the hosting S370 fails the other one should serve clients seeking the PAC file.

[Christian Rahl]

It is possible and has worked for many customers.  The other day I just had a customer that had 12 IP's in the round robin a record list. They have never had any issues with it. 

The one item they kept mentioning was the fact of tracking which boxes had been updated and which ones had not when they made pac file changes.

Christian Rahl

Customer Support Engineer

Cisco Web Content Security Appliance

Cisco Technical Assistance Center RTP

[essam1982]

Thank you for taking time to answer my question Christian.

so I can safely assume that browsers will skip the first IP returned in the DNS query to the next one if the first did not respond to the request?