[dns-operations] Opinions sought .... have I come to the right place?
gwiley at verisign.com
Thu Nov 7 15:18:17 UTC 2013
Be careful about conclusions you may draw from your data.
It may be helpful to remember that many large recursive implementations are comprised of a non-trivial footprint of hosts who may not share a cache across the network. In this case where you may find a TTL respected by a single host behind that recursive server VIP or even across multiple nodes at a single site behind the VIP it is possible that multiple successive queries land on dieffrent nodes with different caches.
The Hive, Verisign, Inc.
From: Edward Lewis <ed.lewis at neustar.biz<mailto:ed.lewis at neustar.biz>>
Date: Thursday, November 7, 2013 9:52 AM
To: DNS Operations <dns-operations at mail.dns-oarc.net<mailto:dns-operations at mail.dns-oarc.net>>
Cc: Edward Lewis <ed.lewis at neustar.biz<mailto:ed.lewis at neustar.biz>>
Subject: [dns-operations] Opinions sought .... have I come to the right place?
I've been studying TTL settings off and on for a few weeks, trying to decide what are appropriate numbers.
In the past we taught the trade-off as - longer TTLs will reduce queries while shorter TTLs will enable agility.
In looking at a set of data with a long TTL - 6 days - over a period of time I noticed that 0.005% of all queriers respected the TTL setting I had. I don't want to fork over details, so you can even say "0.005% +/- 5%" and in any case, it's small. I'll admit by number here might be a little bit of an undercount, still, it's little.
In experimenting with some recursive servers (and by no means an exhaustive set), some code bases did adhere to the "rules" and some code bases seem to ignore the "rules." I say this to the extent that the collective set of deployed tools out there pretty much are eating into the "longer TTLs will reduce queries" part of the above trade-off.
I see that in the IETF there are drafts to pre-fetch expiring data sets - which one can't argue with - but it makes, for an authoritative server operator - even more uncertainty in planning TTLs.
And I'll throw in another factoid from history. During DNSSEC workshops eons ago, we found that is the TTLs got too low, DNSSEC had problems. (Presumably because it took longer to fetch the chain than the TTL of the queried data.) Has anyone found a TTL to be too low for DNSSEC?
So, I'm turning to this list...what is a good range for TTLs?
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