What came first: the CNAME or the A record?

On January 8, 2026, a routine update to the 1.1.1.1 DNS service aimed at reducing memory usage inadvertently caused widespread DNS resolution failures due to a change in the order of CNAME records in DNS responses. This incident highlighted a longstanding ambiguity in DNS protocol specifications, particularly regarding the sequence in which CNAME records should appear relative to other records, an issue rooted in the language of RFC 1034 from 1987. While most modern software is unaffected by the order of DNS records, some implementations, such as Linux's glibc and certain Cisco switches, rely on CNAMEs preceding other records, leading to failures when this order was altered. The incident prompted a reversion of the change and inspired a proposal for a new Internet-Draft aimed at clarifying DNS behavior, which, if accepted, would lead to a formal RFC to eliminate such ambiguities in the future.

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