[80003] in North American Network Operators' Group
Re: Slashdot: Providers Ignoring DNS TTL?
daemon@ATHENA.MIT.EDU (Dean Anderson)
Wed Apr 20 14:01:04 2005
Date: Wed, 20 Apr 2005 14:00:00 -0400 (EDT)
From: Dean Anderson <dean@av8.com>
To: sthaug@nethelp.no
Cc: nanog@merit.edu
In-Reply-To: <10886.1113989651@bizet.nethelp.no>
Errors-To: owner-nanog@merit.edu
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
explained, and was supposed by the poster], there is "some kind of load
balancing going on", and also since implementors of anycast caches have
posted questions and explained their purposes [which could be seen as
"load balancing"], this is a likely explanation. It may not be the only
explanation: e.g. they could be restarting their nameservers every thirty
seconds. But "anycast loadbalancing" of a caching server is probably the
most likely.
But since you post on DNSOP, I assume that you read DNSOP [indeed, I may
assume too much here], and so you have read the recent questions posed
there on just how to implement just this sort of configuration. So, in
light of that, I take your message to be your "usual [and fact-free] rant
against anyone who explains the harms of anycast"
> We use anycast for our caching (recursive) DNS servers. It works well
> for us, and we certainly intend to continue to use it. The actual DNS
> software used is Nominum CNS and BIND 9.3.1, both of which honor the
> DNS TTL.
"worked once for me" doesn't cut it, now. Does it? Probably you didn't
notice that the cache states of different caching servers must be
different. "load balancing" [of nearly any sort] and anycast does not
work so well.
> Steinar Haug, Nethelp consulting, sthaug@nethelp.no
>
>
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