DNS

DNS is the system that translates domain names into IP addresses. It stands for Domain Name System, and it is an Internet Engineering Task Force (IETF) standard name service that lets computers register and resolve domain names.

It makes it possible to assign domain names that are independent of the routing of the numerical IP address, because for humans readable names are easier to remember than IP addresses.

DNS resolution is a very important task because without DNS resolution, the internet would be a very “boring” place..

Sometimes you may get a DNS error because the name did not resolve to the proper IP address. This has several causes:

• The DNS server is down.

• IP connectivity gets lost and thus the DNS cannot resolve

• DNS cache poisoning.

• Update and zone issues.

• The DNS server does not have network connectivity to the root servers.

To find out if your system is resolving properly you can use “nslookup” to verify name resolution. This nslookup command can be used to find details relating to a particular DNS (Domain Name System) like IP address, MX records etc.

Type in nslookup host_name server_IP_address in the command prompt, replacing the actual host name that you are trying to resolve for host_name and the IP address of the DNS server for server_IP_address, then press enter.

Nslookup will also display the various types of DNS records, you can ping with the -a switch to also verify if DNS resolution is working fine.

If a dns server provides incorrect data to queries that it successfully answers, then the most likely causes would be:

• Resource records (RRs) were not dynamically updated in a zone.

• An error was made when manually adding or modifying static resource records in the zone.

• Stale resource records in the DNS server database, left from cached lookups or zone records not updated with current information or removed when they are no longer needed.

If the dns server does not resolve names for external networks, then the causes could be:

• The recursive query times out before it can be completed.

• A remote DNS server fails to respond.

• A remote DNS server provides incorrect data.

• DNS server recursion has been disabled.

You can troubleshoot the connectivity to the root servers to verify that the DNS server used in a failed query can ping its root servers by IP address. If a ping attempt to one root server fails, it might indicate that an IP address for that root server has changed.