Cisco Cisco Web Security Appliance S360 문제 해결 가이드

Contributed by Madhura Kumar and Siddharth Rajpathak, Cisco TAC
Engineers.

Oct 14, 2014

Question
Unable to Resolve the Upgrade Server DNS (Possibly Negative Cache Entries)
     Example

When attempting to upgrade, why do I get the following error:

Failure downloading upgrade list. (Error performing upgrade: I/O error).

Errors when trying to upgrade. Failure downloading upgrade list.

(Error performing upgrade: I/O error opening URL '<download URL>')?

There are a few reasons why this error may occur:

Unable to resolve the upgrade server hostname via DNS (possibly negative cache entries)

• 

The interface being used for upgrades cannot communicate to the upgrades server.

• 

See the solutions for each scenario below.

 To verify if a bad DNS is causing the issue, run the following CLI commands:

WSA.CLI > nslookup downloads.ironport.com

If there are no associated IP addresses returned, run the dnsflush command. This will force the WSA to
re−request DNS for the upgrade server.

Is 'nslookup' of the domain "downloads.ironport.com" successful on the WSA?

−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−

If No, then WSA is unable to resolve the hostname.

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