From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <7c9801f9d6e8edb0f49c8becdd4dc02e@coraid.com>
From: erik quanstrom <quanstro@coraid.com>
Date: Tue,  3 Jul 2007 16:54:31 -0400
To: 9fans@cse.psu.edu
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Subject: [9fans] dns
Topicbox-Message-UUID: 8ff8ec3c-ead2-11e9-9d60-3106f5b1d025

i realize this is apolitical and offtopic.  i apologize in advance.

geoff's improvements in dns are really quite nice.  dns appears do a good
job in the face of well-behaved servers, but there are some ill behaved ones
for popular sites that give me occasional fits.

for example, www.apple.com decided to disappear last evening.  i looked
into the problem and nserver*.apple.com were not reachable.  and the
reason the local nameserver didn't have www.apple.com cached is that
the ttl of www.apple.com is 60 seconds.

interestingly, a dsl modem we have here continued to resolve www.apple.com
during this time, though it also couldn't reach the nameserver.
it seems that the dsl modem's resolver or upstream cache was just
serving up a stale rr.

this is a common problem around here (esp.) for akadns-served sites
with very low ttls.  i'm thinking it would make sense to either
(in order of increasing preference andimplementation difficulty )

a)  ignore very short, but nonzero, ttls and make them at least 3600s.

b)  serve up stale rrs if a fresh answer isn't available up to some multiple
of the real ttl.

c) activly refresh the "most active" cache entries starting at 1/2 the ttl
and increasing in frequency until some mutiple of ttl has expired.

- erik