Skip to main content
protocols.pageprotocols.page
4

NotImp

Not Implemented

Core RCODERFC 1035

NotImp (4) means the DNS server does not support the requested query type or opcode. The server received a valid query but cannot process it because the feature is not implemented. This is distinct from REFUSED (5) where the server understands but declines to answer.

RCODE

4

Name

NotImp

Standard

RFC 1035

Description

NOTIMP is returned when a DNS server receives an opcode or query type it does not implement. The most common case is an UPDATE (RFC 2136) request sent to a server that does not support dynamic DNS updates. Another case: an IQUERY (inverse query, obsoleted in RFC 3425) sent to a modern server. NOTIMP is relatively rare with standard DNS queries (A, AAAA, MX, etc.) because all DNS servers implement basic query handling. It appears when clients try extended DNS operations on servers that predate or exclude those features.

Common Causes

  • –DNS UPDATE (RFC 2136) sent to a server without dynamic DNS support
  • –DSO (DNS Stateful Operations) sent to a non-supporting server
  • –Obsolete opcode (IQUERY) sent to modern server
  • –Experimental query type sent to production server
RFC 1035 – DNS RCODE specification →