Refresh, Expiry and Default TTL

[Brad Knowles]

At 4:34 PM +0100 5/11/01, Matthew Thompson wrote:

>  But I can't decide what the times chould be - does anyone have any
>  suggestions?

	What's your minimum pain threshold?  How long are you willing to 
be "down" before your machines are resolvable again?  If you set the 
TTL too low, can your nameservers take the load?

	These are the kinds of questions you'll need to answer for 
yourself, and once you do, it should become fairly obvious what the 
minimum TTL should be changed to.


	In my experience, if all you're worried about is mail, then one 
hour should probably be fine -- most mail servers kick off a queue 
runner every hour, and if you miss a single queue run on a set of 
machines, you should still be okay.  After you make the change, 
within an hour everyone should see the new addresses.

	If you've got a high-traffic web site, you may want to set the 
TTL down a bit lower, but nothing below five minutes makes sense 
(there are still far too many old nameservers out there that will 
change any numbers lower than five minutes to be exactly five 
minutes, before they store the data).

	Of course, you can change the TTLs on different records to have 
different values, depending on your particular needs.

-- 
Brad Knowles, <brad.knowles at skynet.be>

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