Cisco Cisco Web Security Appliance S170 Guía Del Usuario
D N S A L E R T
C H A P T E R 2 2 : C O N F I G U R I N G N E T W O R K S E T T I N G S
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For example, four DNS servers with two configured at priority 0, one at priority 1, and one at
priority 2:
priority 2:
AsyncOS randomly chooses between the two servers at priority 0. If one of the priority 0
servers is down, the other is used. If both priority 0 servers are down, the priority 1 server
(1.2.3.6) is used, and finally, the priority 2 (1.2.3.7) server.
servers is down, the other is used. If both priority 0 servers are down, the priority 1 server
(1.2.3.6) is used, and finally, the priority 2 (1.2.3.7) server.
The timeout period is the same for both priority 0 servers, longer for the priority 1 server, and
longer still for the priority 2 server.
longer still for the priority 2 server.
DNS Alert
If an alert with the message “Failed to bootstrap the DNS cache” is generated when an
appliance is rebooted, it means that the system was unable to contact its primary DNS
servers. This 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.
appliance is rebooted, it means that the system was unable to contact its primary DNS
servers. This 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.
Clearing the DNS Cache
You can use the Clear DNS Cache button on Network > DNS page, or the
dnsflush
command to clear all information in the DNS cache when changes have been made to your
local DNS system. Using this command might cause a temporary performance degradation
while the cache is repopulated.
local DNS system. Using this command might cause a temporary performance degradation
while the cache is repopulated.
Configuring DNS
To edit DNS Settings:
1. Navigate to the Network > DNS page.
2. Click Edit Settings. The Edit DNS page appears.
Table 22-5 Example of DNS Servers, Priorities, and Timeout Intervals
Priority
Server(s)
Timeout (seconds)
0
1.2.3.4, 1.2.3.5
5, 5
1
1.2.3.6
10
2
1.2.3.7
45