spf-discuss
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Re: How to built an SPF record that is split in substrings?

2004-04-08 00:40:36

Roger Moser wrote:
tdlc.com. 3600 IN TXT (
  "v=spf1"
  "a"
  "mx"
  "-all"
  )

--wayne <wayne(_at_)midwestcs(_dot_)com> wrote:
However, we are not talking about multiple RRs here, we are talking
about multiple substrings on a single TXT RR.  The last time I
checked, I could find nothing in the RFCs that guarenteed that the
substrings will not be rearranged, but in practice, I know of no cases
where the order is not preserved.


For some reason I read this type of record (which I first saw used in MS-CID) and I assumed that the zone file would be read in by a server such as bind, and would be sent as a single string. I don't think there are really such things as multiple substrings in a TXT record once it is sent over the wire to a requester - I believe it will be folded to a single long string in the response (and probably in the transfer to a secondary also).

As used by MS-CID, they definitely were depending on NOT adding spaces, since their example had the strings broken in the middle of a word (or some xml thing that wouldn't work with spaces) if I remember right.

The implication of this is that breaking up a long string this way doesn't make it more appropriate for sending, if the total is over $(PATHMTU) give or take packet header and other fluff you will still have to fall back to TCP to get it all. But it's a cool format for a file especially if you add/reorder stuff often.

--
Greg Connor <gconnor(_at_)nekodojo(_dot_)org>