Benjamin Smith wrote:
>I've been exploring high-uptime availability solutions for our own,
>database-driven ASP. We have two sites, much as original poster describes,
>and 5-minute DNS, but many larger providers (EG: SBC, AOL) have DNS servers
>that seem to ignore TTL.
>
It is important to use TTLs for the various services within a specified
range. Too short will get you ignored, at least after a while. Too
long.. same thing. I've never had a problem with setting the TTLs low
for a few days before a transfer or some such, but then set them back up
into acceptable ranges after the move.
Good help on the proper ranges can be found on http://dnsreport.com
Five minutes will more than likely get you ignored after a few days or
weeks. Imagine if everyone set their TTL to five minutes.. the root
nameservers would be looking up every record on the net once every five
minutes... a pretty arduous task for 13 servers. And if you want to find
out what happens if you don't use cached DNS, try turning it off at the
router level sometime for fun.... s--------l----------o----------w!!!!
Heck, 1200bps dialups act like T-1s compared to no caching.
A side point, I think some have mentioned DNS on Windows boxes. There is
caching of DNS on windows machines as well. This is not a function of
MSIE nor Outlook or whatever application you use, but instead is in some
way central to the network on the system, to which MSIE/etc. makes calls
for DNS. Botched DNS (corruption) will at least take a reboot of the
system.. or a cache flush from the command line. I've seen some things
get cached that requires an edit of a file on the system.. but I don't
remember the location or the name of that file.
Best,
John Hinton
