DNS & Domain Management Flashcards

What is the function of the DNS SOA (Start of Authority) record's 'Refresh' field?

Answer: How often secondary nameservers check for zone updates

The Refresh field tells secondary nameservers how frequently to poll the primary for zone changes.

A CDN customer wants to use their own branded domain (white-label) for the CDN edge URL. Which DNS record type enables this without changing the apex domain?

Answer: CNAME

A CNAME aliases a subdomain (e.g., cdn.example.com) to the CDN's edge hostname, enabling white-label delivery.

Why can't a CNAME record be placed at the zone apex (root domain) in standard DNS?

Answer: RFC 1034 prohibits CNAME coexistence with other record types such as SOA and NS at the same node

RFC 1034 states a CNAME cannot share a node with other records; since the apex needs SOA/NS, a CNAME there is invalid.

What technology do many CDNs offer to work around the CNAME-at-apex limitation?

Answer: ANAME / ALIAS records (flattened CNAME)

ANAME/ALIAS records resolve the CNAME target server-side and return its IPs as an A record, bypassing the apex restriction.

Which DNS query type asks the resolver to return all available record types for a given name?

Answer: ANY (QTYPE=255)

A DNS query with QTYPE=255 (ANY) requests all record types, though many resolvers now limit responses due to amplification abuse.

In the context of CDN DNS management, what is 'split-horizon' (split-brain) DNS?

Answer: Returning different DNS responses to internal vs. external clients for the same hostname

Split-horizon DNS serves different records based on the requester's network, commonly used to route internal traffic off the CDN.

What does a high TTL on a CDN CNAME record negatively impact during a CDN provider migration?

Answer: DNS propagation speed — old IPs stay cached longer across the internet

High TTLs mean resolvers cache the old CNAME target longer, delaying traffic migration to the new CDN provider.