5
DNS
5 REFUSED
Query refused. The name server refuses to perform the requested operation for policy reasons.
Khi bạn thấy mã này
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.
Cách khắc phục
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.
Đặc tả
Các mã tương đương giữa các giao thức
So sánh
So sánh với
Hướng dẫn
HTTP Request Lifecycle: From URL to Response
HTTP Fundamentals
Step-by-Step DNS Troubleshooting with dig and nslookup
Debugging & Troubleshooting
Improving Email Deliverability: SPF, DKIM, and DMARC Setup
Email Delivery
DNS Response Codes (RCODEs) Explained
DNS & Networking
DNS TTL: How to Set TTL Values and Avoid Propagation Delays
DNS & Networking
DNS Propagation: Why Changes Take Time
DNS & Networking
DNSSEC Implementation Guide
DNS & Networking
DNS-Based Failover and High Availability
DNS & Networking
DNS Record Types Explained: A, AAAA, CNAME, MX, TXT, and Beyond
DNS & Networking
DNS over HTTPS (DoH) and DNS over TLS (DoT): Encrypted DNS Explained
DNS & Networking
Essential Network Debugging Tools: ping, traceroute, mtr, and tcpdump
DNS & Networking
Resource Hints: Preload, Prefetch, Preconnect, and DNS-Prefetch
Performance & Optimization
RFC 9114: HTTP/3 Protocol Deep Dive
Protocol Deep Dives
RFC 3261: SIP Protocol Deep Dive
Protocol Deep Dives
QUIC Protocol: The Transport Layer Behind HTTP/3
Protocol Deep Dives
Migrating from TLS 1.2 to TLS 1.3: Configuration and Compatibility
Migration & Upgrades
Secret Management for API Keys, Tokens, and Certificates
Production Infrastructure
Tình huống gỡ lỗi
Đặc tả
Hướng dẫn quyết định
Thuật ngữ
TCP/IP
Port Number
Latency
Timeout
Firewall
DNS over HTTPS (DoH)
IPv6
Subnet (Subnetwork)
MTU (Maximum Transmission Unit)
UDP (User Datagram Protocol)
DNS Lookup
CDN (Content Delivery Network)
Request-Response Model
RFC (Request for Comments)
IANA (Internet Assigned Numbers Authority)
Wire Format
Extension Mechanism
Connectionless
Text vs Binary Protocol
DNS Resolution
DNS Record Types
TTL (Time to Live)
DNSSEC (DNS Security Extensions)
DNS over TLS (DoT)
Anycast
Recursive Resolver
Authoritative Name Server
Glue Record
EDNS(0)
DNS Zone
DNS Propagation
CNAME Record
MX Record
SRV Record
PTR Record
DNS Cache Poisoning
DNS Root Server
Split-Horizon DNS
Wildcard DNS Record
SPF, DKIM, and DMARC
Email Deliverability
MTA (Mail Transfer Agent)
ARC (Authenticated Received Chain)
BIMI (Brand Indicators for Message Identification)
Service Discovery
GSLB (Global Server Load Balancing)
Failover
Active-Passive HA