Hey Jullan,
Thank you for the reply -- my problem isn't how to compose a
multi-part SPF message inside a TXT record.
The problem I see is how PowerDNS (mis-)behaves when trying to serve a
non-compliant record.
PowerDNS returns NOERROR for the status and then returns a malformed message.
I understand the argument of bad data in, bad data out; I would
rather see PowerDNS not return bad data though.
--Augie
On Wed, Mar 24, 2010 at 6:14 PM, Julian Mehnle jul...@mehnle.net wrote:
Augie Schwer wrote:
PowerDNS returns a malformed response when queried for a TXT record
larger than 257 characters.
[...]
PowerDNS returns NOERROR and returns as much data as it can which ends
up creating the corrupt packet.
Admittedly one shouldn't put bad data in (the above record is not RFC
compliant); I was hoping PowerDNS would handle the response better --
any of the response codes could fit and certainly not return a
malformed packet; I'd rather see an empty packet or maybe a truncated
RDATA and a NOERROR return code.
The problem is that while a TXT record can contain multiple strings (the
parts you have to enclose in double quotes in TXT records in both BIND
and PowerDNS), each string can only be 256 bytes long at maximum by design
-- one length octet plus 255 bytes of text (RFC 1035). If you want to
have a longer TXT record, you have to split it into several strings, like
so:
v=spf1 ip4:209.204.164.194 a mx mx:gordonmedical.com,
mx:mailin-02.mx.sonic.net,mx:g.mx.sonic.net, mx:mailin-01.mx.sonic.net,
mx:e.mx.sonic.net mx:a.mx.sonic.net, mx:c.mx.sonic.net,
mx:d.mx.sonic.net, mx:h.mx.sonic.net, mx:f.mx.sonic.net, mx:and
mx:b.mx.
leaving a space between strings like so: string1 string2. The SPF
spec states that multiple strings will be concatenated seamlessly, so
you'd probably have to include another space *in* the strings, either at
the end of string1 or at the start of string2.
Note that this is different from splitting the record into several
*records* (opposed to several strings in a single record). This doesn't
work with SPF since ordering among records is undefined by DNS and SPF
wouldn't know how to concatenate them correctly.
Of course you could just remove the erroneous commas and fix up the SPF
record to get below the 256 characters limit in this particular case.
-Julian
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--
Augie Schwer-au...@schwer.us-http://schwer.us
Key fingerprint = 9815 AE19 AFD1 1FE7 5DEE 2AC3 CB99 2784 27B0 C072
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