puzzling dnscache behavior

Nicholas Leippe nick at leippe.com
Wed Jun 18 16:13:19 MDT 2008


I use dnscache on my workstation.

Everything worked fine until recently. I don't know exactly when the behavior 
changed.

The behavior is thus:

If I query for rss.slashdot.org:

# dnsqr a rss.slashdot.org

It times out, and the dnscache log shows the typical "servfail 
rss.slashdot.org. input/output error" which isn't very meaningful.

However, if I first do:

# dnsqr cname rss.slashdot.org
5 rss.slashdot.org:
68 bytes, 1+1+0+0 records, response, noerror
query: 5 rss.slashdot.org
answer: rss.slashdot.org 3453 CNAME feeds.feedburner.com

then it works:

# dnsqr a rss.slashdot.org
1 rss.slashdot.org:
84 bytes, 1+2+0+0 records, response, noerror
query: 1 rss.slashdot.org
answer: rss.slashdot.org 3450 CNAME feeds.feedburner.com
answer: feeds.feedburner.com 153 A 66.150.96.119

It continues to work for a while, before it reverts. (Most likely a 
timeout/ttl is occurring.)

I have env/FORWARDONLY set to 0 (to make it recur) and root/servers/@ is 
simply the list of root servers.

Any ideas?





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