What came first: the CNAME or the A record?
19 days ago
- #CNAME
- #DNS
- #RFC1034
- A routine update to 1.1.1.1 on January 8, 2026, caused DNS resolution failures due to a change in the order of CNAME records in DNS responses.
- Some DNS clients, like glibc's getaddrinfo and certain Cisco switches, expect CNAME records to appear before other records, leading to failures when the order was altered.
- The issue stemmed from a memory optimization change that inadvertently reordered CNAME records to appear after resolved answers in DNS responses.
- RFC 1034 ambiguously suggests CNAME records should 'possibly preface' answers but does not mandate a strict order, leading to varied client implementations.
- The incident was resolved by reverting the change, and a proposal was drafted to clarify CNAME handling in DNS responses for future standardization.