SERVFAIL

SERVFAIL is a DNS response code used to indicate that a server was unable to process a query due to a general problem on the server side. In the DNS protocol, SERVFAIL corresponds to the RCODE value 2 and is defined in the standards that govern domain name system messages. It signifies that the failure is not a simple non-existence (NXDOMAIN) or a refused operation, but rather an unexpected condition that prevented obtaining a valid answer.

In practice, SERVFAIL can be produced by recursive resolvers, authoritative servers, or during interactions between them. It may occur when a server cannot complete the request because of internal errors, misconfigurations, resource exhaustion, or an inability to reach required upstream data. It can also arise from failures related to DNSSEC validation, data integrity checks, or problems encountered while performing zone transfers or contact with authoritative servers.

Common causes include software bugs or crashes, insufficient memory or processing capacity, network connectivity issues to upstream or upstream dependencies, timeouts, misconfigured zone data, missing glue records, and DNSSEC-related validation failures. Because SERVFAIL reflects a server-side problem, it is distinct from cases where the queried name simply does not exist or is not delegated.

Impact and troubleshooting: clients may receive SERVFAIL from recursive resolvers, which can lead to widespread resolution failures until the underlying problem is resolved. Operators should examine server and system logs, verify configuration and zone data, check connectivity to authoritative servers, and test queries directly against authoritative sources. Tools such as dig or drill, with careful inspection of EDNS, DNSSEC status, and trace paths, can help identify where the failure originates.