[dns-operations] forward compression pointers?

Roy Arends roy at dnss.ec
Wed Sep 2 18:21:19 UTC 2009

On Sep 2, 2009, at 12:37 PM, Ray.Bellis at nominet.org.uk wrote:

> > >   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.
> Indeed, but as Mark points out this _example_ in 5625 was based on  
> the text from 1035 which says that a compression pointer may only  
> point to a _prior_ occurrence of the same name.
> That clearly (IMHO) prohibits a pointer that points to itself.


Parsing loops may not solely be caused by a forward pointer, hence  
Robert Edmonds note that "RFC 5625 section 6.3 which could be  
construed to imply that forward pointers may be dropped" is not  
correct, or at least incomplete, as 5625 does not mention forward  
pointers, just examples of packets that do not do proper compression.

Kind regards,


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