A social networking company operates globally. Some users from Brazil and Argentina are reporting the following error: website address was not found. Which of the following is the most likely cause of this outage?

Because only users located in Brazil and Argentina are unable to resolve the site while the service remains reachable elsewhere, the failure scope matches the public-resolver infrastructure that serves that geographic region. A regional DNS provider (for example, the recursive resolver network of a large telco or anycast node set that answers queries in South America) being offline or mis-routing traffic would return NXDOMAIN/timeout to every client behind it, producing the “website address was not found” message. An authoritative-side or global-propagation problem would affect all users worldwide, and individual client misconfiguration would not simultaneously impact many unrelated users.

A. Client DNS misconfiguration – Would be isolated to single hosts or small groups, not thousands of users across two countries.
C. DNS server (authoritative) misconfiguration – Would break name resolution for every region, not just South America.
D. DNS propagation issues – New/updated records propagate within TTL globally; unresolved records would appear inconsistently worldwide, not strictly limited to one geographic area.

1. RIPE NCC

“DNS for Operators – Causes of Regional Resolver Failure

” ripe-714

§3.2 (pp. 8-9).

2. Google Cloud Documentation

“Designing resilient Cloud DNS architectures

” High-Availability Design > Regional resolver outages (2022)

para. 4.

3. Moura

G. C. M. et al.

“Anycast vs. DDoS: Evaluating Regional DNS Resilience

” ACM SIGCOMM CCR 47(3)

2017

pp. 14-18. DOI:10.1145/3131345.3131350

4. MIT OpenCourseWare

6.033 “Computer Systems Engineering

” Lecture 9 notes

slide 15: ‘Failure domains in DNS (local resolvers vs. authoritative)’.

5. IETF RFC 8499

“DNS Terminology

” §2.1

explains differing failure scopes of recursive resolvers vs. authoritative servers.