The DNS (Domain Name System or Service) is an Internet service that translates domain names (which are easier for humans to remember) into IP addresses (which computer use to address each other). Every time you use a domain name, therefore, a DNS service must translate the name into the corresponding IP address. For example, the domain name www.paessler.com might translate to 62.146.51.168.

The DNS sensor sends a request to resolve a specific domain name to an IP address to the server it is associated with. This is useful e.g. to ensure that a company's web server address can be resolved by the outside world or to check a DNS server in a LAN for availability.

Note: The server associated with this sensor has to be a DNS server and not the domain name of the server you want to monitor.

If you only enter the domain name PRTG Network Monitor will only check whether the name is resolved to an IP address at all (which simply means that the DNS server works correctly and the domain name is valid). If you also enter an IP address the resolved IP address will be compared to this and the sensor will show an error when the two addresses are different.

Parameters include:

• Timeout: If the reply takes longer than this value the request is aborted and an error message is triggered
• Port: Define the DNS port
• Domain: Enter the domain name to look up (e.g. www.yourcompany.com)
• IP Address: Optionally enter an IP address to compare the result with
• DNS Server: You can select to use the primary DNS server or specify the IP / DNS name of a specific DNS server to check against