Does a caching-nameserver usually cache the negative DNS response SERVFAIL

Question

Does a caching-nameserver usually cache the negative DNS response SERVFAIL?

EDIT: To clarify the question, I can see the caching nameserver caching negative responses NXDOMAIN, NODATA. But it does not do this for SERVFAIL responses. Is this intentional?

Answer 1

SERVFAIL is covered by §7.1 of RFC2308:

Server failures fall into two major classes. The first is where a server can determine that it has been misconfigured for a zone. This may be where it has been listed as a server, but not configured to be a server for the zone, or where it has been configured to be a server for the zone, but cannot obtain the zone data for some reason. This can occur either because the zone file does not exist or contains errors, or because another server from which the zone should have been available either did not respond or was unable or unwilling to supply the zone.

The second class is where the server needs to obtain an answer from elsewhere, but is unable to do so, due to network failures, other servers that don't reply, or return server failure errors, or similar.

In either case a resolver MAY cache a server failure response. If it does so it MUST NOT cache it for longer than five (5) minutes, and it MUST be cached against the specific query tuple <query name, type, class, server IP address>.

So basically, it's dependent on the implementation of your name server.

Answer 2

RFC 1034 describes how to cache negative responses but did not define a mechanism for returning those cache results to peer resolvers. RFC 2308 defines these attributes.

Negative caching was an optional part of the DNS Specifications...