How not to set up your DNS (part 17)

August 16, 2007

Here is an interesting one that caused me to go digging into the moderate depths of DNS arcana:

; sdig ns
; dig mx
;; [...] status: SERVFAIL, [...]

This isn't for any simple reason, such as the servers refusing to answer us or not being authoritative or whatnot. Instead, they have managed to get the 'no such record' reply wrong; instead of returning a SOA record for, they return what looks like a lame delegation response (pointing at themselves), except that it has the aa bit set.

What may be going on is that seems to be running a very peculiar nameserver that has the moral equivalent of a wildcard CNAME record for, but only for A record queries; if you ask directly for a CNAME for, you get a normal 'no such data' reply, but if you ask for the A record for that you get back a reply with a CNAME plus an A record. Presumably as a result of this, almost all queries for MX records of names inside the zone get these lame delegation replies.

(Not all MX queries; MXes to, and will return an MX record for that.)

Written on 16 August 2007.
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Last modified: Thu Aug 16 12:23:50 2007
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