[dns-operations] forward compression pointers?
roy at dnss.ec
Wed Sep 2 10:00:08 UTC 2009
On Aug 30, 2009, at 10:59 PM, Robert Edmonds wrote:
> are there any DNS responders that generate forward compression
> or DNS initiators that reject them?
I haven't seen one in the wild that create them. I have build a test-
server thinghy that responds with forward pointers to see how
resolvers behave. There are resolvers that reject them, and that
follow them., and that go completely bezerk.
> i note RFC 5625 section 6.3 which could be construed to imply that
> pointers may be dropped, since forward pointers "might cause a
> parsing loop":
> Examples of malformed packets that MAY be dropped include:
> o invalid compression pointers (i.e., those that point outside of
> the current packet or that might cause a parsing loop)
I can't construe from that sentence alone that forward pointers may be
dropped, for instance, a pointer to the exact location of that pointer
is not a forward pointer, but can still cause loops.
> but 5625 is BCP, not standards track. c.f.,
> Idea #3: DNS Name Compression Standards
> A draft mandating the DNS name compression only be done in one
> direction. Virtually all (or perhaps even actually all)
> implementations have DNS compression pointers only pointing to
> earlier in the message. This draft would propose that
> forward-pointing compression pointers should be treated as format
> errors. This would accomplish two things:
> 1. Simplify what implementers need to support when parsing
> messages, and
> 2. outlaw any possibility of having to deal with a compression
> pointer loop.
> And, in the process, effectively codify standard practice.
IMHO, this BCP does not violate any [proposed] STD.
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