On Thu, Dec 02, 2010 at 10:16:58AM -0500, Richard Pieri wrote:
> On Dec 2, 2010, at 1:28 AM, Derek Martin wrote:
> To the contrary, running a local cache provides superior lookup
> times for all but the first lookup in all but the most dodgy edge
> cases.

You're missing the point.  Your statement is true, as far as it goes;
but what is an end-user going to notice more?  The average case of a
locally cached DNS lookup taking a few milliseconds less time, or the
edge case of uncached or expired lookups taking 10s longer?  Edge
cases do matter if they happen enough, and perception is reality. 

> The CDN argument falls flat.  If the CDN looks at the ISP's source
> addresses on DNS lookukps then it still isn't going to get you
> something geographically local.  

It doesn't matter if it's geographically local... all that matters is
network topology.  It's rare that an ISP's DNS servers are not
topologically closer to their end users than... well, much of anything
else.  It does happen, but it's an edge case that can be identified
by CDNs and worked around in other ways, once traffic is actually
being served to those IPs.

> The super-short TTL argument falls even flatter.  Suffice it to say
> that DNS roulette is not load balancing.  There have been many
> papers written about why it is bad practice.  

Any technical arguments against it do nothing to change the fact that
its use is widespread.

-- 
Derek D. Martin    http://www.pizzashack.org/   GPG Key ID: 0xDFBEAD02
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