Cisco Cisco Email Security Appliance C160 Mode D'Emploi

A record does not exist, the system only uses the IP address to match entries in 
the Host Access Table (HAT).] This particular timeout period applies only to this 
lookup and is not related to the general DNS timeout discussed in 

.

The default value is 20 seconds. You can disable the reverse DNS lookup timeout 
globally across all listeners by entering ‘0’ as the number of seconds. If the value 
is set to 0 seconds, the reverse DNS lookup is not attempted, and instead the 
standard timeout response is returned immediately.

Occasionally, an alert may be generated with the message “Failed to bootstrap the 
DNS cache” when an appliance is rebooted. The messages means that the system 
was unable to contact its primary DNS servers, which can happen at boot time if 
the DNS subsystem comes online before network connectivity is established. If 
this message appears at other times, it could indicate network issues or that the 
DNS configuration is not pointing to a valid server.

The Clear Cache button from the GUI, or the d

nsflush

 command (for more 

information about the 

dnsflush

 command, see the Cisco IronPort AsyncOS CLI 

Reference Guide), clears all information in the DNS cache. You may choose to use 
this feature when changes have been made to your local DNS system. The 
command takes place immediately and may cause a temporary performance 
degradation while the cache is repopulated.

Log in to the Graphical User Interface (GUI) and click the DNS link on the 
Network tab.