Load balancing? problem...

Re: Load balancing? problem...

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At 11:59 AM -0600 11/18/01, <listaccount@starionline.com> wrote:
>Did I read on this list somewhere that when DNS is queried, the server that
>responds fastest will be the response that is used? For example, our
>primary DNS is on a machine that is slower than the secondary. Which would
>explain why the secondary sees a lot more "traffic"....is that theory right?

That is sometimes the case, but not always. Here are three examples
of how a DNS server might find information in your zones:

- Server receives the delegation records pointing to your servers. It
knows nothing about the current state of your servers, so it queries
them all and takes the first response it gets.

- Server receives the delegation records pointing to your servers. It
knows nothing about the current state of your servers, so it picks
one at random (the first listed in the delegation, which actually may
not be so random) and queries it. If that server doesn't respond
before some timeout limit (often 5 seconds or less, depending on
implementation), it queries the other server. (If you have more than
one other, it may query them all, or it may pick another at random.)

- Server receives the delegation records pointing to your servers. It
has recent data about the responsiveness of your servers; it has a
rating system for each server. It queries the best-rated server from
your list. If your server responds, its rating is dropped by one step
- this is so that the resolving server will at some point try your
other servers again. If the server queried does not respond, its
rating is dropped significantly; the other server(s) is/are queried,
as described in the previous example.

Which method(s) is/are used depends entirely on the implementation.
For all I know, there may be other methods, too.
____________________________________________________________________
Chris Buxton Men & Mice
support@menandmice.com Making DNS Easy

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