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ProtocolCodes
23
DNS

23 BADCOOKIE

Bad or missing server cookie. The DNS COOKIE option in the request is absent, malformed, or does not match the server's expected value.

On this page

When You See This Code

Your resolver sent a query without a valid server cookie, or the cookie has expired. This is part of the DNS COOKIE mechanism to prevent spoofed-source attacks.

How to Fix

Retry the query — most resolvers automatically learn the correct server cookie from the first response. If the error persists, ensure your resolver supports RFC 7873 DNS Cookies.

Specification

View RFC / Specification →

Compare With

0 NOERROR 1 FORMERR 2 SERVFAIL 3 NXDOMAIN 4 NOTIMP 5 REFUSED 6 YXDOMAIN 7 YXRRSET 8 NXRRSET 9 NOTAUTH 10 NOTZONE 11 DSOTYPENI

Guides

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

Glossary

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

Frequently Asked Questions

What is DNS 23 BADCOOKIE?

Bad or missing server cookie. The DNS COOKIE option in the request is absent, malformed, or does not match the server's expected value.

When do you see DNS 23 BADCOOKIE?

Your resolver sent a query without a valid server cookie, or the cookie has expired. This is part of the DNS COOKIE mechanism to prevent spoofed-source attacks.

How to fix DNS 23 BADCOOKIE?

Retry the query — most resolvers automatically learn the correct server cookie from the first response. If the error persists, ensure your resolver supports RFC 7873 DNS Cookies.