The answer is the AAAA record and the PTR record, which are the two DNS record types most commonly used together to verify both forward and reverse DNS mappings for an IPv6 address. The AAAA record, often called a Quad-A record, maps a domain name to a 128-bit IPv6 address, enabling forward lookups, while the PTR record performs the reverse mapping by translating an IPv6 address back to a hostname. On the CCNA 200-301 v2 exam, this concept tests your understanding of DNS resolution in dual-stack environments, where verifying consistency between forward and reverse records is critical for services like email delivery and security logging. A common trap is confusing the AAAA record with the older A record, which only supports IPv4, or assuming a CNAME or MX record could handle reverse verification. To remember this, think of the double A in AAAA as standing for “Address for IPv6,” and pair it with PTR as “Pointer to Reverse”—together they ensure your IPv6 mappings are fully validated.
CCNA Network Services and Security Practice Question
This 200-301 practice question tests your understanding of network services and security. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Which TWO DNS record types are most commonly used together to verify both forward and reverse DNS mappings for an IPv6 address?
Why wrong: An A record maps a hostname to an IPv4 address, not an IPv6 address.
B
AAAA record
The AAAA record is the standard record type for mapping a domain name to an IPv6 address.
C
CNAME record
Why wrong: A CNAME record is an alias that points one domain name to another, not directly to an IP address.
D
PTR record
A PTR record performs reverse DNS lookup, mapping an IP address (including IPv6) back to a domain name. It is used to verify the reverse mapping for an IPv6 address.
E
MX record
Why wrong: MX records specify mail exchange servers for a domain, not IP address mappings.
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.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 hostname to an IPv4 address, not an IPv6 address.
✓
AAAA record
Why this is correct
The AAAA record is the standard record type for mapping a domain name to an IPv6 address.
Related concept
Read the scenario before looking for a memorised answer.
✗
CNAME record
Why it's wrong here
A CNAME record is an alias that points one domain name to another, not directly to an IP address.
✓
PTR record
Why this is correct
A PTR record performs reverse DNS lookup, mapping an IP address (including IPv6) back to a domain name. It is used to verify the reverse mapping for an IPv6 address.
Related concept
Read the scenario before looking for a memorised answer.
✗
MX record
Why it's wrong here
MX records specify mail exchange servers for a domain, not IP address mappings.
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
The AAAA record is the standard record type for mapping a domain name to an IPv6 address.
✗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?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
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).
Detailed technical explanation
How to think about this question
When using dig to query for an IPv6 address, the command 'dig domain.com AAAA' queries the DNS for the Quad-A record, which returns a 128-bit IPv6 address in the answer section. For reverse DNS verification, the PTR record is stored in the ip6.arpa zone, where the IPv6 address is nibble-swapped into a reverse lookup name; tools like dig -x <IPv6-address> automate this process. In real-world scenarios, mismatched forward (AAAA) and reverse (PTR) records can cause email delivery failures or authentication issues in protocols like SMTP and SSH.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A junior network technician can log in to a core router but cannot reach the enable prompt or configuration mode. The AAA server is authenticating the login — but the authorisation policy only grants privilege level 1, not 15. Authentication (who you are) is working; authorisation (what you can do) is not.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 question in full detail.
Network Services and Security — This question tests Network Services and Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: 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.
What should I do if I get this 200-301 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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