Re: [dnsext] RETRY and EXPIRE clarification

[Edward Lewis <[e-mail]>]

At 10:18 +0200 10/5/11, Lubos Slovak wrote:
>Hi,
>
>I find the definition of RETRY and EXPIRE intervals in RFC 1035 
>quite vague and did not find any other RFC clarifying it.

First lesson in reading RFC 1034/1035 - don't take them that 
literally.  They were descriptions of the system, not specifications. 
This was explained to me by one of the folks involved in writing them.

>1) Should the RETRY interval start when the REFRESH event occurred (this
>is a bit more deterministic) or when it is clear that the transfer failed,
>i.e. on timeout or error during transfer (this is maybe closer to the
>definition of RETRY in RFC 1035, part 3.3.13)?

Doesn't really matter, I mean, how long does it take to fail a 
transfer?  Let's say it's 90 seconds - if the retry is 43200 (12 
hours), whether you try 1/2 a day later or 1/2 day plus 90 seconds 
later isn't going to change things.  It looks cooler in the logs if 
the retries happen at the stroke of 1/2 day intervals, but it doesn't 
matter in the long run.

>2) What should happen if the EXPIRE interval elapses before the transfer is
>finished (assume large zone, transfer lasts for several minutes and EXPIRE is
>set too low - i.e. 1 minute)? Should the server cease to serve the zone? If
>yes, should it serve the zone again after the transfer is finished?

Could and yeah.  I suspect that while you are transferring the zone 
you can suspend checking the timer if you want and no one would 
complain.

EXPIRE shouldn't be that low though.  DNS wasn't built to be real 
time, when you have a server-cache-client architecture you can expect 
it to be that fast.

(There's nothing wrong in trying to make DNS be real time.  But 
you'll have to realize it takes some work as that wasn't the design 
goal.  Kind of like trying to drag race pickup trucks.  You can do 
it, but it isn't as easy or efficient as drag racing speedsters.)
-- 
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Edward Lewis
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