Cisco Cisco Email Security Appliance C170 Guia Do Utilizador

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 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.

Select Network > DNS.

Click Edit Settings. 

Select whether to use the Internet’s root DNS servers or your own internal DNS server or the Internet’s 
root DNS servers and specify alternate DNS servers. 

If you want to use your own DNS server(s) enter the server ID and click Add Row. Repeat this for each 
server. When entering your own DNS servers, specify a priority as well. For more information, see 

.

If you want to specify alternate DNS servers for certain domains, enter the domain and the alternate DNS 
server IP address. Click Add Row to add additional domains.

You can enter multiple domains for a single DNS server by using commas to separate domain 
names. You can also enter multiple DNS servers by using commas to separate IP addresses.

Choose an interface for DNS traffic.

Enter the number of seconds to wait before cancelling a reverse DNS lookup.

You can also clear the DNS cache by clicking Clear Cache.

Submit and commit your changes.

Some network environments require the use of traffic routes other than the standard default gateway. You 
can manage static routes via the GUI through the Routing page on the Network tab, or the CLI, via the 

routeconfig

 command.