Which DNS record maps a hostname to an IPv4 address?
A record: maps a name to a 32-bit IPv4 address. The AAAA record does the same for IPv6 (128-bit) addresses.
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What does a CNAME record do?
CNAME: a canonical name record creates an alias so one domain points to another name, which is then resolved. You cannot place a CNAME at the zone apex alongside other records per RFC.
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What is the role of the TTL on a DNS record?
TTL (time to live): the duration in seconds that a resolver may cache the record before re-querying. Lower TTLs speed propagation of changes but increase query load.
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Which record type is used by email delivery to find a domain's mail servers?
MX record: specifies mail exchange servers and a preference value; lower preference numbers are tried first. SPF/DKIM/DMARC policies live in TXT records.
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What does an authoritative nameserver provide?
Authoritative nameserver: holds the original zone data and gives definitive answers for those domains. A recursive resolver, by contrast, queries others and caches results on behalf of clients.