CCNA Network Services and Security Practice Question
Which TWO DNS record types are most commonly used together to verify both forward and reverse DNS mappings for an IPv6 address?
⚠ Common exam trap
Cisco often tests the misconception that an A record can be used for IPv6 addresses, but the A record is strictly for IPv4 (RFC 1035), while the AAAA record is the correct type for IPv6 (RFC 3596).
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
AAAA record
The AAAA record (Quad-A record) maps a domain name to an IPv6 address, making it the standard type for forward IPv6 lookups. The PTR record performs the reverse mapping—from an IPv6 address back to a domain name. Administrators routinely check both records with tools like nslookup or dig to ensure forward and reverse DNS consistency, which is critical for services such as email and security logging. The other options (A, CNAME, MX) do not directly provide a domain-to-IPv6 mapping or its reverse verification.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
A record
Why it's wrong here
An A record maps a fully qualified domain name to an IPv4 address, providing forward resolution. It cannot hold an IPv6 address, and it does not perform reverse lookups. The question requires a record type that maps an IPv6 address back to a domain name, so an A record is incorrect.
- ✓
AAAA record
Why this is correct
An AAAA record is the forward-DNS record that maps a hostname to a 128-bit IPv6 address, analogous to an A record for IPv4. It is commonly used for hostname-to-address resolution, not for address-to-hostname resolution. Since the question requires reverse mapping from an IPv6 address back to a name, an AAAA record does not fulfill that purpose.
- ✗
CNAME record
Why it's wrong here
A CNAME record creates an alias by pointing one hostname to another canonical hostname, which ultimately resolves via A or AAAA records. It cannot directly map an IP address to a domain name, and RFC 1034 prohibits its use in reverse-map zones. Thus, it is not the right record type for this reverse IPv6 lookup scenario.
- ✓
PTR record
Why this is correct
A PTR record is the DNS resource record type used exclusively for reverse lookups, translating an IP address (IPv4 or IPv6) back to a canonical hostname. For IPv6, these records reside in the ip6.arpa zone and are essential for verifying reverse mappings of addresses. This is exactly what the scenario asks for, making it the correct answer.
- ✗
MX record
Why it's wrong here
An MX record identifies the mail exchange server responsible for accepting email on behalf of a domain, along with a priority value. It has nothing to do with mapping IP addresses to hostnames, and it is not involved in reverse DNS lookups. Therefore, it is completely irrelevant for verifying an IPv6 reverse mapping.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓AAAA recordCorrect answer▾
Why this is correct
An AAAA record is the forward-DNS record that maps a hostname to a 128-bit IPv6 address, analogous to an A record for IPv4. It is commonly used for hostname-to-address resolution, not for address-to-hostname resolution. Since the question requires reverse mapping from an IPv6 address back to a name, an AAAA record does not fulfill that purpose.
✗A recordWrong answer — click to see why▾
Why this is wrong here
An A record maps a hostname to an IPv4 address, not an IPv6 address. Since the question specifically asks about IPv6, this record type is incorrect.
Why candidates choose this
Students often confuse A and AAAA records because both are used for forward DNS resolution. The similar naming and purpose (mapping names to IPs) make A records a common distractor.
✗CNAME recordWrong answer — click to see why▾
Why this is wrong here
A CNAME record creates an alias from one domain name to another, not a direct mapping to an IP address. It does not provide the IP address itself, so it cannot verify the mapping to an IPv6 address.
Why candidates choose this
CNAME records are commonly used and can indirectly point to an IPv6 address via the target domain's AAAA record. Students may think that querying a CNAME will reveal the IPv6 address, but it only returns the canonical name.
✗MX recordWrong answer — click to see why▾
Why this is wrong here
MX records specify mail exchange servers for a domain and are used for email routing, not for mapping domain names to IP addresses. They do not provide IPv6 address mappings.
Why candidates choose this
MX records are a well-known DNS record type, and students might think they are used for general IP mapping due to their importance in email delivery. However, they are unrelated to IPv6 address verification.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Visual reference
Quick reference
Common DNS Record Types
| Record | Purpose | Example |
|---|---|---|
| A | IPv4 address mapping | example.com → 93.184.216.34 |
| AAAA | IPv6 address mapping | example.com → 2606:2800::1 |
| CNAME | Alias to another hostname | www → example.com |
| MX | Mail server for domain | example.com → mail.example.com (priority 10) |
| TXT | Text data (SPF, DKIM, verification) | v=spf1 include:_spf.example.com ~all |
| NS | Authoritative name servers | example.com NS ns1.example.com |
| PTR | Reverse DNS (IP → hostname) | 34.216.184.93.in-addr.arpa → example.com |
| SOA | Zone authority record | Primary NS, admin email, serial, TTL defaults |
Go deeper
Related to this question
Learn chapter
RA Guard — IPv6 First-Hop Security
Key term
IPv6 address
An IPv6 address is a 128-bit numeric label used to identify a device on an Internet Protocol network, designed to replace IPv4 due to the exhaustion of available addresses.
Key term
Fully Qualified Domain Name
A Fully Qualified Domain Name is the complete and unambiguous website or server name that includes the host, domain, and top-level domain, leaving no room for guesswork.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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