D-Link NetDefendOS User Manual page 152

gw-world:/> dns -cache
An example of output from this command is shown below:
gw-world:/> dns -cache
Name
---------------------------------- ---------- ------ --------------------
my_fqdn_address1
my_fqdn_address2
The status of a particular FQDN in the cache can be examined with the following command:
gw-world:/> dns -cache <FQDN>
Where <FQDN> is the logical configuration name of the address object in the address book.
Below is a example of output from this command:
gw-world:/> dns -cache my_fqdn_address1
Address : my_fqdn_address1
Status : Resolved
IP address
--------------------------------------------------
203.0.113.3
This information about the DNS cache can also be accessed in the Web Interface by going to
Status > Run-time Information > DNS Cache.
The Cache is Automatically Updated
When the DNS server returns IP addresses for an FQDN Address object, it also returns a Time To
Live (TTL) value. This value is stored with the entry for the FQDN Address object in the DNS cache.
When the TTL expires, NetDefendOS will refresh the cache entry by issuing a new DNS query.
The TTL returned from the DNS server could be very low or even zero. For this reason,
NetDefendOS provides a global DNS setting called Minimum TTL. If the TTL returned from a DNS
server is less than the value of Minimum TTL, the TTL is reset to be the Minimum TTL value.
There is also a second global DNS setting called Minimum Cache Time. This value becomes the
TTL if it greater than the TTL from the DNS server. However, the TTL value from the DNS server is
used if it is greater than the Minimum Cache Time setting.
Associated Log Messages
NetDefendOS can generate the following log messages associated with FQDN Address objects:
• ipv4_max_addresses - The 128 IPv4 address limit is exceeded and addresses from the DNS
server have been dropped.
• ipv6_max_addresses - The 128 IPv6 address limit is exceeded and addresses from the DNS
server have been dropped.
• dns_no_record - The DNS server does not have a record for the FQDN and it cannot be
resolved.
• dns_timeout - The DNS server has timed out during the FQDN lookup.
• dns_error - An unspecified error occurred during DNS lookup.
Status IP Cnt Address
Resolved
Unused
152
Chapter 3: Fundamentals
1 server1.example.com
0
LifeTime
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299