Is caching necessary?
Brad Knowles
brad at stop.mail-abuse.org
Sat Apr 30 13:38:08 UTC 2005
At 11:45 PM -0400 2005-04-29, Kevin Darcy wrote:
> The only legitimate reason for forwarding to a central cache, when one
> has the option available to query Internet nameservers directly, is if
> the constellation of local network topology, query patterns, TTL values,
> etc. happen to all align so as to make your average and/or worst-case
> query latency better that way.
No, there's another legitimate reason. When you have a business
need to guarantee that all internal servers see the same answers for
a given question (modulo TTLs), but you can't point all those servers
directly at a single caching/recursive server.
For example, at AOL I had a problem where mail would come in from
a given sender to a given recipient via one particular server, and
everything would work fine. However, mail from the same sender to
the same recipient via a different server would find different
information in the DNS (perhaps the delegation was broken, or there
was a lame server, or somesuch), and we would end up rejecting the
message.
Try doing that with ten million users, handling tens of millions
of messages per day, and even if this kind of thing only has a
one-in-a-thousand chance of happening, that means you have a very
large number of extremely irate customers who are all looking to use
explosive devices in new and creative ways.
Performance is one valid reason where forwarding may be used, but
there are others.
--
Brad Knowles, <brad at stop.mail-abuse.org>
"Those who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety."
-- Benjamin Franklin (1706-1790), reply of the Pennsylvania
Assembly to the Governor, November 11, 1755
SAGE member since 1995. See <http://www.sage.org/> for more info.
More information about the bind-users
mailing list