How does the DNS resolution work on the ProxySG?
If the ProxySG receives a negative DNS response (a response with an error code set to Name Error), it caches that negative response. You can configure the ProxySGs negative response time-to-live value. (A value of zero disables negative caching.) If the dns negative-cache-ttl-override is not configured (this is the default ProxySG setting), the ProxySG caches the negative response and uses the TTL value from the DNS response to determine how long it should be cached. Please see the Command Line Interface (CLI) Reference for further information regarding the “dns negative-cache-ttl-override” setting. The CLI reference can be downloaded from https://bto.bluecoat.com/documentation/pubs/ProxySG/ .