The DNS Lookup Tool is used for querying DNS name servers. It performs DNS look-ups and displays the answers that are returned from the name server(s) that were queried.

Background

An IP Address (Internet Protocol Address) is the addressing mechanism used to locate computers and other devices on the Internet. An IP address (IP version 4) is made up of four values ranging from 0 to 255 separated by dots (E.g. 127.0.0.1). This is convenient for identifying and locating computers but is not very "human friendly". This is akin to identifying people by their telephone numbers - and only their telephone numbers.

DNS (Domain Name System) was created to act as a sort of "telephone book" to identify the "IP address" of Domain Names which are more easily remembered. (E.g. whitehouse.com is really 173.223.96.110)

E-mail is tightly bound to DNS records, which are used to identify how an e-mail message is to be routed across the Internet. If there are problems with DNS resolution then e-mail delivery is prevented.

Also, DNS records are used to validate the sending domain of an e-mail. Mail servers will reject e-mail originating from domain names that do not exist. Once again, problems with DNS resolution can result in message rejections for domains that cannot be verified by the mail server.

In e-mail diagnostics, first verify that network connectivity exists then check that DNS resolution is functioning correctly.

DNS Lookup Tool

The DNS Lookup Tool can be used to troubleshoot DNS problems. The DNS Lookup Tool options are described, below:

DNS Server - The DNS Server specifies the DNS server you want to query. You can specify a particular DNS server or select from a list of local and publicly available DNS servers. (If DNS servers are experiencing problems they may give incorrect results, so it is best to verify against more than one DNS server.)

Look-up Name - The IP address, domain, or host name to be queried.

Record Type - The DNS record type to look-up. There are a number of record types available, the most popular are listed below:

• A - Address records (IPv4);
• MX - Mail Exchanger Record, used to identify mail servers for e-mail delivery;
• NS - Name Server Record;
• TXT - Text record, used to hold SPF records among other things;
• X - Reverse Look-up, used to easily extract the PTR record of a supplied IP Address;
• Trace - This option traces the delegation path from the root servers for the name being looked up. Iterative queries are made to identify and follow referrals from the root servers, showing the answer from each server that was used to resolve the look-up.