[dns-operations] Who Ignores TTLs ?

Paul Vixie vixie at isc.org
Tue Feb 22 01:19:49 UTC 2011

> From: Warren Kumari <warren at kumari.net>
> Date: Mon, 21 Feb 2011 19:29:09 -0500
> > i think you could get that benefit at the http layer, and that doing it
> > in dns isn't nec'ily called for by this particular application.
> Yes, but this would require at least one more http round trip, yes?
> Not (necessarily) an issue for something like a mirror, ...

i was speaking specifically in the context of a distro mirror, but...

> ...but for folk who have lots of short lived connections this adds up
> *real* quick. It also requires a single (or small number) of central
> locations that need to a: be really really reliable and b: able to
> perform a huge number of redirects, doesn't it?

...no.  if a web site's internal links are relative, then the first
redirect will affect all the other fetches as wel.  furthermore,
http/1.1 means you'll tend to fetch a lot of objects over each tcp/80
session.  so even if a browser opens multiple tcp/80 sessions to the
"web server" in order to parallelize, the number of redirects will
be much lower than the number of objects.

noting that tcpct (RFC 6013) offers the possibility of additional
savings in the important "time to first eyeball" metric, even greater
than the best possible results from any conceivable non-tcpct cdn
technology.  i hope this means our grandchildren will have a cleaner
design to work with.

More information about the dns-operations mailing list