1.6 - DNS record types

Network+ N10-009 objective 1.6 covers DNS and its record types, which the exam tests directly. An A record maps a hostname to an IPv4 address, and an AAAA record maps a hostname to an IPv6 address. An MX record directs email delivery for a domain to its mail servers. A PTR record builds the reverse (IP-to-name) zone for reverse lookups. An SRV record lets a service such as SIP advertise its host and port. You should also know CNAME (an alias to another name), TXT (used for SPF, DKIM and verification), NS (name servers) and SOA (zone authority). Expect scenario questions that describe what a lookup needs to return - an IPv6 address, mail routing, a reverse name, a service location - and ask which DNS record type provides it.

Memory hook
Name to IPv4 = A; to IPv6 = AAAA. Email routing = MX. Reverse (IP-to-name) = PTR. Service host+port = SRV. Alias to another name = CNAME. SPF/DKIM/verification = TXT.

Practice questions

1. Which DNS record maps a hostname to an IPv6 address?

  • A
  • AAAA (correct answer)
  • CNAME
  • PTR

AAAA (quad-A) records map a name to a 128-bit IPv6 address. A maps to IPv4, CNAME is an alias, PTR does reverse lookups.

2. Which DNS record directs email delivery for a domain?

  • TXT
  • SRV
  • MX (correct answer)
  • NS

MX (Mail Exchanger) records name the mail servers and their priority for a domain. TXT holds text (SPF/DKIM), SRV locates services, NS lists nameservers.

3. Which DNS record type is used to build the reverse (IP-to-name) zone?

  • PTR (correct answer)
  • A
  • SRV
  • TXT

PTR records map an IP back to a hostname in the in-addr.arpa zone (reverse DNS). A maps name to IPv4, SRV locates services, TXT holds text.

4. Which DNS record lets a service like SIP advertise its host and port?

  • A
  • MX
  • CNAME
  • SRV (correct answer)

SRV records publish the host, port, priority and weight for a service (e.g., SIP, LDAP). MX is mail-specific, CNAME is an alias, A maps to IPv4.

5. Which DNS record creates an alias pointing one name to another name?

  • A record
  • PTR record
  • CNAME (correct answer)
  • NS record

A CNAME (canonical name) points one hostname to another name rather than to an IP. A points to IPv4, PTR is reverse, NS delegates a zone.

6. Which DNS record holds SPF, DKIM or domain-verification text?

  • TXT (correct answer)
  • MX
  • SRV
  • AAAA

TXT records store arbitrary text such as SPF, DKIM and domain-ownership tokens. MX routes mail, SRV locates services, AAAA maps IPv6.

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