Redundant DSL Questions?!

Re: Redundant DSL Questions?!

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At 8:54 AM -0400 4/21/00, andrew kagan wrote:
><snip>
>> this can be mitigated by setting the
>> TTL's of the A records for the web server to low values - 300 seconds
>> (5 minutes) or less.
>
>Wouldn't this create an enormous increase in DNS querying?

I don't think so. When you think about it, how many different
visitors do you get that use the same resolver? Besides, how much of
your traffic is DNS queries? Even if you increase the amount of DNS
traffic by an order of magnitude, is it a large percentage of the
total?

One resolver may be able to handle as much as a few thousand actual
users requesting recursive resolution at any given time. Now try to
imagine what percentage of the total Internet community actually
visits your site in a given day. Even if you just consider the
Internet users of your own country, you'll probably get a pretty low
percentage. Multiply that rough percentage by the number of users any
given name resolver can service, and you get a rough idea of how
useful caching really is.

For really popular sites, like Apple, Yahoo, Ebay, etc., caching will
be useful. However, some of the most popular sites are setting their
TTL's very low - Amazon.com and Barnes & Noble both have the TTL's of
the A records for their web servers set to 0, for load balancing
purposes. Yahoo has theirs set to 300 (5 minutes), again for load
balancing purposes.

For any given user, once they've found your site, they won't send
more queries. Browsers don't respect TTL's.

For your mail servers, leave the TTL's at the default setting
(usually 1 day), but put in two MX records (one for each address).
Mail service is designed around fault tolerance.

--

Please bear in mind that these are my own thoughts and opinions, and
do not represent official opinions of Men & Mice. If anybody would
like to discuss (or dispute) my theories, please do so - especially
if you have hard data to back you up. I frankly don't have any real
data of my own.

Has anybody using our load balancing and fault tolerance mechanism
noticed a large increase in DNS traffic? After all, it defaults to a
TTL of 300 for a load balance record.
____________________________________________________________________
Chris Buxton cbuxton@menandmice.com
Men & Mice http://www.menandmice.com
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