[80078] in North American Network Operators' Group
Re: Slashdot: Providers Ignoring DNS TTL?
daemon@ATHENA.MIT.EDU (Stephen J. Wilcox)
Sat Apr 23 05:22:36 2005
Date: Sat, 23 Apr 2005 10:22:03 +0100 (BST)
From: "Stephen J. Wilcox" <steve@telecomplete.co.uk>
To: Dean Anderson <dean@av8.com>
Cc: sthaug@nethelp.no, <nanog@merit.edu>
In-Reply-To: <Pine.LNX.4.44.0504222325260.6185-100000@cirrus.av8.net>
Errors-To: owner-nanog@merit.edu
On Fri, 22 Apr 2005, Dean Anderson wrote:
> On Thu, 21 Apr 2005, Stephen J. Wilcox wrote:
>
> > On Wed, 20 Apr 2005, Dean Anderson wrote:
> >
> > > On Wed, 20 Apr 2005 sthaug@nethelp.no wrote:
> > >
> > > > > I'd rather expect this sort of behavior with anycasted servers...
> > > >
> > > > Where do you see any connection between anycast and ignoring DNS TTL? Or is
> > > > this just part of your usual rant against anycast DNS service?
> > >
> > > The data he showed isn't necessarilly "ignoring ttl". If there are multiple
> > > anycasted caching servers behind a specific IP address, then those several
> > > cache's will each have a different state. Since, [as I
> >
> > I fail to see the correlation still.. anycasted caches should all be operating
> > independently getting their DNS data from authoritative sources.
> >
> > If at any point one of them uses a TTL that it has not received from the
> > authoritative source it is ignoring the ttl, where does anycast get involved
> > with this particular problem?
>
> The queries produce different data, but none of the data is inconsistent
> if there are different caches responding on the same address. Here is the
> original description: (slightly reformated with roman numerals)
>
> (I) I ran a query for a name in a zone I control that has a five minute
> TTL on 204.127.198.4. The first query came up with 5 minutes.
> (II) I quickly made a change to the zone.
> (III) Thirty seconds after the initial query, I try
> again...err... and come up with the change. Hmm... Not caching at all?
> (IV) Another 30 seconds and I get the change, with 5m TTL.
> (V) Thirty seconds later, I get the original response with appropriately
> decremented TTL.
> (VI) Another thirty seconds, I get the change, with 4m TTL.
>
> Here is the detailed anycast explanation:
> (I) Cache 1 gets answer to query X? = Y
> (II) Authority changes X? to Z
> (III) Cache 2 gets answer to query X? = Z
> (IV) Cache 3 gets answer to query X? = Z
> (V) Cache 1 responds
> (VI) Cache 3 responds
>
> No TTLs were ignored.
Ok gotcha, and you point seems valid except aiui the previous post was
concerning providers who are actually overriding the TTL eg your zone has a 5m
ttl, the provider caches it but sets TTL to 10 days.
i think this thread forked quite early :)
Steve
