DNS Records

Question 1

A / AAAA records

Answer 1

Address records are how the DNS database keeps track of the names of individual systems on a network. Each individual A record associates one name with an IPv4 address, and each AAAA record associates one name with an IPv6 address. If you need to associate a human-friendly name like “accounting” with the accounting department’s file server, you’ll create an A or AAAA record.

Question 2

MX records

Answer 2

MX records enable the servers that handle outgoing e-mail to figure out where e-mail for each domain should go. I let Microsoft 365 handle my e-mail, so the MX record for totalsem.com points to the domain that Microsoft 365 uses for incoming mail. If you shoot me an e-mail at mike@totalsem.com, your outgoing mail server will look up the MX record and know to send the mail on to Microsoft’s server.

MX officially stands for mail exchange, though the CompTIA A+ 1101 objectives use the term mail exchanger.

Question 3

TXT records

Answer 3

Text (TXT) records are the junk drawer of the DNS database. People use these free-form records to hold all kinds of things—but the CompTIA A+ 1101 objectives only want you to know the role they play in spam management. For decades e-mail administrators waged a battle with scammers who send mountains of unwanted e-mail—spam—24 hours a day. To that end, TXT records have three anti-spam purposes:

• DomainKeys Identified Mail (DKIM) records Enable receiving servers to verify that the messages they receive were signed by the sending server and have not been altered by intermediate servers.
• Sender Policy Framework (SPF) records List the IP or DNS addresses allowed to send e-mail for a domain, enabling receiving servers to discard or flag messages sent by illegitimate servers.
• Domain-based Message Authentication, Reporting, and Conformance (DMARC) records Enable domain owners to indicate what receiving servers should do with e-mail that fails the DKIM or SPF checks. They also enable domain owners to receive reports from large e-mail providers about the origin of the mail they received from the domain.