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At 7:40 AM -0400 9/24/01, andrew kagan wrote:
Re: weird dns error resolving "www"
From: Men & Mice Support
Date: Monday, September 24, 2001
Time: 7:05:08 am
>that sound's really lame...the whole point of having multiple NS is so that
>if one goes down, queries for the domain will still resolve. What you're
>telling me is if an NS goes down, other NS's won't query the working NS and
>will just timeout...so what's the point of the redundancy?
No, that's not right. If a server goes down, at worst, there should
be no more than a 1 second delay before a query is considered "late".
The resolving server will still wait longer for it to respond, but it
will also query the other listed servers.
And after that first query, the resolving server should have in cache
the fact that a given server doesn't respond.
When I try to look up the records in question, there is a delay for
the first query that a given resolving server is asked. The
subsequent, different query is returned only a couple of hundred
milliseconds more slowly than a repeated query (i.e. cached data). I
repeated this test with several resolving servers, including a few
that had to cross oceans.
That first-query delay could easily be the result of:
- Asking the gTLD servers where to find the authoritative servers
(often takes more than a second, as the gTLD servers don't always
respond).
- Randomly choosing to query the down server first (or the lame server).
>Again, my lack of knowledge about DNS is showing...is is something like if
>one NS gets an authoritative answer from another NS, it will continue to tr=
y
>that NS AND ONLY that NS until domain's TTL expires? Is that what's
>happening here?
No, it's supposed to be more fault-tolerant than that.
Are you still experiencing this problem?
____________________________________________________________________
Chris Buxton Men & Mice
cbuxton@menandmice.com We Make DNS Easy!
>I'm really trying to understand what's going on here. Thanks for your help
>to this point.
>
>Andrew
>
>
>----- Original Message -----
>From: "Len Conrad" <LenConrad@MenAndMice.com>
>To: "QuickDNS Talk" <quickdns-talk@lists.menandmice.com>
>Sent: Monday, September 24, 2001 6:42 AM
>Subject: Re: weird dns error resolving "www"
>
>
> >
> > >"something" is needed to explain the huge discrepancy in the www respo=
nse
> > >above.
> >
> > And I think I know what that something is. In my first query, my NS
> > 212.73.210.69 probably got the answer from your two responding NS's. I=
n
> > the second query, it probably used ns2 first, timed out since that box =
is
> > dead, and then queried one of the responding NS's.
> >
> > If you cannot get ns2 back on-line quickly, I suggest you change the
>domain
> > registration to exclude ns2. Some NS's and resolvers and broswers
>time-out
> > on ns2 and perhaps are falling over to using alternative NS=B4s.
> >
> > Len
> >
> > ___________________________________________________________________
> >
> > Men & Mice: QuickDNS - DNS Expert - DNS Training - DNS Consulting
> > DNS Classes: Newark Sep 27-28, Toronto Oct 18-19, Frankfurt Nov 21-23=
,
> > London Nov. 26-28, Maidenhead Oct 31-Nov 2
> > http://MenAndMice.com/DNS-training
> >
> >
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