puzzling dnscache behavior
amb-plug at bradfords.org
Mon Jun 23 22:52:52 MDT 2008
Thus said Nicholas Leippe on Mon, 23 Jun 2008 09:31:51 MDT:
> @40000000485fbfb7348a66bc query 50884 7f000001:5f46:f243 1 rss.slashdot.org.
It looks like another query came in just 3 seconds after the one at the
beginning of the log:
> @40000000485fbfba35ae7c2c query 50885 7f000001:7efa:3108 1 rss.slashdot.org.
It also looks like you may not have captured the log at the actual
beginning of the error:
> @40000000485fbfba3814e53c servfail rss.slashdot.org. input/output error
> @40000000485fbfba3814f0f4 sent 50879 34
Where are the logs for query 50879? The logs here start with query 50884.
> @40000000485fbfd91461c40c servfail rss.slashdot.org. input/output error
> @40000000485fbfd91461d3ac sent 50884 34
So it took 34 seconds for the query to eventually time out. Question is
why? It looks like the last query it made for rss.slashdot.org was to
220.127.116.11. It also made queries to 18.104.22.168 which failed. This
log snippet doesn't appear to have any queries made to 22.214.171.124,
their other NS server. The queries to the first two servers appear to
time out after 34 seconds, so basically it looks like a problem with at
least these two servers. Either they are having intermittent problems or
there is a firewall blocking these somewhere.
What happened in the 3 minutes inbetween these two (failure and
successful) logs? When it gets into a failure situation again, attempt
to query their servers directly:
dnsq cname rss.slashdot.org 126.96.36.199
dnsq cname rss.slashdot.org 188.8.131.52
dnsq cname rss.slashdot.org 184.108.40.206
Assuming of course they haven't changed their NS records in that amount
of time (which may actually be a possibility).
See if they respond.
Also, if you can get the relevant parts of the log for the queries prior
to 50884 (like 50879 and possibly others) from the very first time it
fails, we may be able to glean more.
10:52pm up 1:59, 1 user, load average: 1.01, 1.00, 1.00
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