[dns-operations] Opinions sought .... have I come to the right place? (Recommended TTL)

Bob Harold rharolde at umich.edu
Thu Nov 7 16:01:06 UTC 2013

Disclaimer: I don't officially speak for the university.

Both here and in a previous job at a multi-national company, we tried to
standardize on 30 minutes.  The reason is that when a server has problems
and someone comes running to us to get a DNS change to get the users
working again, a half hour seems like a long time to be down, especially
with manufacturing plants losing money at ridiculous rates for any
downtime.  I don't want to have to tell the user it will take hours or days
for a DNS change, or ask him to find everyone around the world that happens
to be trying to reach his service to tell them to reboot their PC or clear
their DNS cache - that is generally impossible.

I realize that 30 minutes might increase the load on my DNS servers, but
with modern servers I am generally buying the smallest server I can find
for local DNS resolvers, and it is still bigger than I really need.
(Although recent attacks have changed that.)

Some users want faster updates, so some records are set to 5 minutes.  And
sites that do load balancing or sharing by changing DNS records use 0, 1,
or 5 seconds.  I try to avoid zero because I expect that some software
won't handle that.

We do not use DNSSEC yet, so I have no experience with that.

Bob Harold
DNS and DHCP, University of Michigan

Date: Thu, 7 Nov 2013 09:52:57 -0500

> From: Edward Lewis <ed.lewis at neustar.biz>
> To: DNS Operations <dns-operations at lists.dns-oarc.net>
> Cc: Edward Lewis <ed.lewis at neustar.biz>
> Subject: [dns-operations] Opinions sought .... have I come to the
>         right   place?
> Message-ID: <0C72B731-82F9-4898-837F-3657EF0B6AAC at neustar.biz>
> Content-Type: text/plain; charset="us-ascii"
> I've been studying TTL settings off and on for a few weeks, trying to
> decide what are appropriate numbers.
> ...

> So, I'm turning to this list...what is a good range for TTLs?
> -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
> Edward Lewis
> NeuStar                    You can leave a voice message at
> +1-571-434-5468
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