Intelligent DNS???? anyone!!!

[Kevin Darcy]

hallian at hotmail.com wrote:

> hi all,
>
> I was wondering are there any DNS servers out there which are
> intelligent enough to direct every 10th request to a bunch of servers.
>
> for example: 10th 20th 30th 40th request go to serverA otherwise all
> the other request goto serverB.

BIND doesn't support this directly. You could approximate it somewhat by
assigning 9 times as many different addresses to serverB -- through
"virtual" interfaces, or via some form of NAT -- than you do to serverA.
This would result in serverB getting approximately 90% of the hits and
serverA getting 10%, however, because of the random element (even the
default "cyclic" sort order is not true round-robin, despite what the
BIND documentation would lead you to believe), you may occasionally see
"spikes" of higher-than-usual activity on one server or the other. So
it's far from a "perfect" solution.

Even if, theoretically, true round-robin were resurrected in BIND, you'd
still have to deal with all of the intermediate caching servers out there
which will answer from their cached data using "cyclic" or some other
randomness-tainted sort order. The all-too-common way of dealing with the
effects of caching servers is to reduce the TTLs on the relevant records,
but this wastes DNS resources and is generally bad for the Internet.


- Kevin