By DNS protocol specification (RFC 1034 and RFC 2181), CNAME records should only point to domain names, not IP addresses. The correct record type for IP resolution is an A record (or AAAA for IPv6). When you attempt to create a CNAME pointing to an IP like xxx.xxx.xxx.xx1, you're technically violating RFC standards.

; Non-compliant but sometimes functional CNAME example
subdomain.example.com. IN CNAME 192.168.1.1.

Some DNS resolvers exhibit lenient behavior due to:

• Recursive resolver forgiveness: Services like Google's 8.8.8.8 may attempt to "fix" malformed records
• Caching weirdness: Stale cache entries from previous A record resolutions
• Local network overrides: Corporate DNS may have internal rewrite rules

Your diagnostic output reveals the critical evidence:

;; ANSWER SECTION:
somesubdomain.somedomain.com. 67 IN CNAME xxx.xxx.xxx.xx1.

;; AUTHORITY SECTION:
. 1800 IN SOA a.root-servers.net...

The NXDOMAIN response indicates the root servers ultimately reject this configuration, despite temporary local resolution.

For reliable subdomain resolution:

; Correct implementation
subdomain IN A 192.168.1.1
; OR for aliasing
subdomain IN CNAME canonical.example.com.

Modern DNS validation tools will flag IP CNAMEs:

# Using dnsvalidator
$ dnsvalidate --zonefile example.com.db
ERROR: CNAME at subdomain points to IP (192.168.1.1)

When debugging intermittent resolution:

1. Check multiple resolvers (8.8.8.8, 1.1.1.1, local ISP)
2. Inspect TTL values and wait for cache expiration
3. Verify with dig +trace for full resolution path

• ❌ Never use CNAME for IP addresses
• ✅ Use A/AAAA records for direct IP resolution
• ✅ Use CNAME only for domain aliasing
• ✅ Implement DNSSEC to prevent cache poisoning

While RFC standards explicitly state that CNAME records should point to domain names (not IP addresses), there are documented cases where CNAME-to-IP configurations appear to work temporarily. This occurs due to:

// Example of invalid but sometimes functional DNS record
somesubdomain IN CNAME 192.0.2.1

The intermittent functionality stems from how different DNS resolvers handle non-compliant records:

• Lenient Resolvers: Some public DNS servers (like older BIND versions) would attempt to "help" by treating the IP as a hostname
• TTL Caching: The record might have worked during the TTL window before stricter resolvers refreshed their cache
• Corporate DNS Middleware: Some enterprise firewall/DNS systems automatically rewrite malformed records

Current implementations (like dig 9.16+) strictly enforce RFC compliance:

// Expected error in modern systems
$ dig @8.8.8.8 badcname.example.com
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 12345
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1

For reliable DNS configuration:

// Correct implementation options
// Option 1: Standard A record
subdomain IN A 192.0.2.1

// Option 2: CNAME to properly configured hostname
subdomain IN CNAME realhost.example.com.
realhost IN A 192.0.2.1

Major DNS providers now actively prevent CNAME-to-IP configurations through validation checks during record creation.

When investigating DNS anomalies:

1. Check multiple resolvers (8.8.8.8, 1.1.1.1, local ISP)
2. Test with different tools (dig, host, nslookup)
3. Examine full DNS response headers

# Diagnostic command sequence
dig +trace +additional somesubdomain.example.com
dig +short TXT debug.dns.example.com