networking protocol_error ai_generated true

DNS: CNAME resolution loop detected for www.example.com (max depth 16 exceeded)

ID: networking/dns-dangling-cname

Also available as: JSON · Markdown · 中文
95%Fix Rate
90%Confidence
1Evidence
2024-01-10First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
BIND 9.18.12 active — — —
Unbound 1.17.0 active — — —
PowerDNS Authoritative Server 4.8.0 active — — —

Root Cause

A DNS zone contains a chain of CNAME records that ultimately points back to itself, creating an infinite loop that exceeds the resolver's maximum query depth (typically 16) and causes a resolution failure.

generic

中文

DNS区域中包含一条CNAME记录链，最终指向自身，形成无限循环，超过解析器的最大查询深度（通常为16），导致解析失败。

Official Documentation

https://www.rfc-editor.org/rfc/rfc1034#section-5.2.2

Workarounds

  1. 95% success Identify and break the CNAME loop by inspecting the zone file: dig www.example.com CNAME +trace; then remove or correct the circular reference in the DNS provider's control panel. 
    Identify and break the CNAME loop by inspecting the zone file: dig www.example.com CNAME +trace; then remove or correct the circular reference in the DNS provider's control panel.
  2. 90% success Temporarily replace the CNAME record with an A record pointing to the correct IP address to restore service while investigating the loop. 
    Temporarily replace the CNAME record with an A record pointing to the correct IP address to restore service while investigating the loop.
  3. 88% success Use a DNS debugging tool like dnstracer to visualize the CNAME chain: dnstracer www.example.com -s . -r 20 
    Use a DNS debugging tool like dnstracer to visualize the CNAME chain: dnstracer www.example.com -s . -r 20

中文步骤

  1. Identify and break the CNAME loop by inspecting the zone file: dig www.example.com CNAME +trace; then remove or correct the circular reference in the DNS provider's control panel.
  2. Temporarily replace the CNAME record with an A record pointing to the correct IP address to restore service while investigating the loop.
  3. Use a DNS debugging tool like dnstracer to visualize the CNAME chain: dnstracer www.example.com -s . -r 20

Dead Ends

Common approaches that don't work:

  1. 98% fail

    The loop is in the authoritative DNS zone, not in the client cache; flushing will just re-fetch the same broken records.

  2. 85% fail

    This only delays the failure; the loop will eventually hit the new limit and still fail. It also increases resource usage for legitimate queries.

  3. 70% fail

    This is too aggressive; the loop is caused by a specific CNAME chain, not all records. Removing everything may break other services.