DNS кеширане

DNS кеширанетo повишава производителността на DNS системата в една организацията, като намалява времето, необходимо да предостави DNS заявки. Когато един DNS сървър реши успешно дадено име го добавя в своята памет и така с течение на времето изгражда записи на имена и домейни и свързаните с тях адреси за най-общи домейни, които организацията използва или подстъпва.

По подразбиране времето за кеширане на данните в DNS-а е един час. Това може да се
конфигурира за определените DNS зони.

Клиентския DNS кеш е този, който се запазва на локалния компютър. За да видите този кеш можете да използвате командата ipconfig/displaydns в cmd.
Ако искате да изчистите този кеш може да използвате командата ipconfig /flushdns

 Също можете да използвате следните Windows PowerShell cmdlets:

• clear-DnsClientCache to delete the DNS resolver cache

  

• get-DnsClientCache to view the resolver cache

 

Мониториране на DNS чрез DNS Event Log

 

DNS сървъра има своя категория  логове в Event Viewer, който трябва да се наблюдава периодично.

В таблицата по-долу може да видите най-честите DNS събития.

 

Event ID	Description
2	The DNS server has started. This message generally appears at startup when either the server computer or the DNS server service is started.
3	The DNS server has shut down. This message generally appears when either the server computer is shut down or the DNS server service is stopped manually.
408	The DNS server could not open socket for address [IPaddress]. Verify that this is a valid IP address for the server computer. To correct the problem, you can do the following: 1. If the specified IP address is not valid, remove it from the list of restricted interfaces for the server and restart the server. 2. If the specified IP address is no longer valid and was the only address enabled for the DNS server to use, the server might not have started because of this configuration error. To correct this problem, delete the following value from the registry and restart the DNS server: HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\DNS\Parameters\ListenAdd

3. If the IP address for the server computer is valid, verify that no other application that would attempt to use the same DNS server port, such as another DNS server application, is running. By default, DNS uses TCP port 53.

Event ID	Description
413	• The DNS server sends requests to other DNS servers on a port other than its default port, TCP port 53. • This DNS server is multihomed and has been configured to restrict DNS server service to only some of its configured IP addresses. For this reason, there is no assurance that DNS queries made by this server to other remote DNS servers will be sent by using one of the IP addresses that was enabled for the DNS server. • Using a port other than port 53 might prevent query answer responses that these servers return from being received on the different DNS port that the server is configured to use. To avoid this problem, the DNS server sends queries to other DNS servers using an arbitrary non-DNS port, and the response is received regardless of the IP address used. • If you want to limit the DNS server to using only its configured DNS port for sending queries to other DNS servers, use the DNS console to perform one of the following changes to the server properties configuration on the Interfaces tab: • Select All IP addresses to enable the DNS server to listen on all configured server IP addresses. • Select Only the following IP addresses to limit the IP address list to a single server IP address.
414	The server computer currently has no primary DNS suffix configured. Its DNS name currently is a single label host name. For example, its configured name is host rather than host.example.microsoft.com or another FQDN. Although the DNS server has only a single label name, default resource records created for its configured zones use only this single label name when mapping the host name for this DNS server. This can lead to incorrect and failed referrals when clients and other DNS servers use these records to locate this server by name. In general, you should reconfigure the DNS server with a full DNS computer name that is appropriate for its domain or workgroup use on your network.
708	The DNS server did not detect any zones of either primary or secondary type. It will run as a caching-only server, but will not be authoritative for any zones.
3150	The DNS server wrote a new version of zone [zonename] to file [filename]. You can view the new version number by clicking the Record Data tab. This event should appear only if you configure the DNS server to operate as a root server.
6527	Zone [zonename] expired before it could obtain a successful zone transfer or update from a master server that is acting as its source for the zone. The zone has been shut down. This event ID might appear when you configure the DNS server to host a secondary copy of the zone from another DNS server that is acting as its source or master server. Verify that this server has network connectivity to its configured master server. If the problem continues, consider one or more of the following options: 1. Delete the zone and recreate it, specifying either a different master server or an updated and corrected IP address for the same master server. 2. If zone expiration continues, consider adjusting the expiration interval