On Sat, 13 Aug 2005, wayne wrote:
Don't most resolvers deal with this automatically and leave the
application no control over this?
Are you saying that SPF implementations need to bypass standard
resolvers and do special checking?
The socket.h gethostbyaddr() family API follows CNAME for you. However,
SPF implementations can't use that layer anyway, since the gethostbyaddr()
style functions don't let you query TXT (or SPF or MX). Furthermore,
implementations concerned about latency will want to issue multiple queries in
parallel (e.g. query both TXT and SPF and use the first that arrives).
When the resolver API lets you query by name,class,type (e.g. "man resolver" -
resolv.h in Linux), then CNAME is just another query type, and you lookup
the next name yourself as needed if that's what you want.
So, yes SPF implementations need to bypass the simplified
gethostbyaddr() family API, and use the resolver API - in which
CNAME is just another type of record.
Pyspf uses the DNS package which is equivalent to resolv.h, but implemented
in Python (instead of wrapping the C API).
--
Stuart D. Gathman <stuart(_at_)bmsi(_dot_)com>
Business Management Systems Inc. Phone: 703 591-0911 Fax: 703 591-6154
"Confutatis maledictis, flamis acribus addictis" - background song for
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