DNS 1 FORMERR vs 4 NOTIMP
Both DNS 1 (FORMERR) and 4 (NOTIMP) belong to the DNS Response Codes (RCODEs) category. 1 indicates that format error. The name server was unable to interpret the query due to a malformed DNS message. Meanwhile, 4 means that not Implemented. The name server does not support the requested query type or operation.
Description
Format error. The name server was unable to interpret the query due to a malformed DNS message.
When You See It
Your DNS client or library sent a query the server could not parse, often caused by a buggy resolver, corrupted packet, or unsupported EDNS options.
How to Fix
Check your DNS client or library version for known bugs. Capture the raw query with dig or Wireshark and verify it conforms to the DNS wire format.
Description
Not Implemented. The name server does not support the requested query type or operation.
When You See It
You sent a query type (e.g., IXFR, dynamic update) that the server does not support or has disabled.
How to Fix
Verify the server supports the query type you are using. If you need zone transfers or dynamic updates, enable them in the server configuration.
Key Differences
DNS 1: Format error. The name server was unable to interpret the query due to a malformed DNS message.
DNS 4: Not Implemented. The name server does not support the requested query type or operation.
You encounter 1 when your DNS client or library sent a query the server could not parse, often caused by a buggy resolver, corrupted packet, or unsupported EDNS options.
You encounter 4 when you sent a query type (e.g., IXFR, dynamic update) that the server does not support or has disabled.
When to Use Which
For 1 (FORMERR): Check your DNS client or library version for known bugs. Capture the raw query with dig or Wireshark and verify it conforms to the DNS wire format. For 4 (NOTIMP): Verify the server supports the query type you are using. If you need zone transfers or dynamic updates, enable them in the server configuration.