DNS 5 REFUSED vs 21 BADALG
Both DNS 5 (REFUSED) and 21 (BADALG) belong to the DNS Response Codes (RCODEs) category. 5 indicates that query refused. The name server refuses to perform the requested operation for policy reasons. Meanwhile, 21 means that algorithm not supported. The cryptographic algorithm specified in the TKEY or SIG record is not supported by the server.
描述
Query refused. The name server refuses to perform the requested operation for policy reasons.
何时出现
The server rejected your query due to access control — for example, a recursive resolver that only serves its own network, or a zone transfer blocked by ACL.
如何修复
Check the server's allow-query, allow-recursion, or allow-transfer ACLs. If you are not authorized to use this resolver, switch to a public DNS service.
描述
Algorithm not supported. The cryptographic algorithm specified in the TKEY or SIG record is not supported by the server.
何时出现
Your TKEY negotiation or DNSSEC operation requested an algorithm (e.g., HMAC-SHA512) that the server has not been compiled with or configured to accept.
如何修复
Use a mutually supported algorithm. HMAC-SHA256 is widely supported for TSIG; for DNSSEC, check the server's supported algorithm list with its documentation.
主要区别
DNS 5: Query refused. The name server refuses to perform the requested operation for policy reasons.
DNS 21: Algorithm not supported. The cryptographic algorithm specified in the TKEY or SIG record is not supported by the server.
You encounter 5 when the server rejected your query due to access control — for example, a recursive resolver that only serves its own network, or a zone transfer blocked by ACL.
You encounter 21 when your TKEY negotiation or DNSSEC operation requested an algorithm (e.g., HMAC-SHA512) that the server has not been compiled with or configured to accept.
何时使用哪个
For 5 (REFUSED): Check the server's allow-query, allow-recursion, or allow-transfer ACLs. If you are not authorized to use this resolver, switch to a public DNS service. For 21 (BADALG): Use a mutually supported algorithm. HMAC-SHA256 is widely supported for TSIG; for DNSSEC, check the server's supported algorithm list with its documentation.