[dns-operations] Too Open (Was: OpenDNS makes your Internet work better

Paul Vixie paul at vix.com
Wed Jul 19 17:12:59 UTC 2006

> >> They cease to be sent. 8-) AFAIK, most DNS resolvers keep track which
> >> servers are down (or are lame) and query them only occasionally, to see
> >> if the problem still persists.  Some of them even store the RTT.
> >
> > As far as I know this is *not* true for many stub resolvers (e.g. your
> > typical Unix libresolv).

BIND's res_send() has had logic like this inside it since 4.9 or so.  Not
the RTT sorting thing, just the don't-keep-retrying-dead-servers thing.

> Ah, good point.  I had authoritative name servers on my mind, despite
> the subject of the thread.  Resolvers face very different issues.

Authoritative name servers don't send queries, so I think what you mean is
"caching recursive nameservers" (which RFC 1034 calls "full resolvers") as
opposed to "BIND's resolver library" (which RFC 1034 calls a "stub resolver.")

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