DNS name pointer
Barry Margolin
barmar at alum.mit.edu
Wed Apr 26 05:11:36 UTC 2006
In article <e2m8t1$2fkg$1 at sf1.isc.org>,
Kevin Darcy <kcd at daimlerchrysler.com> wrote:
> Rohit Tandon wrote:
>
> >Hi All,
> >
> >I was wondering if the NAME pointers that are used during compression
> >of a DNS packet can actually point to another pointer within the DNS
> >message. Is there any restriction that pointers should point to only
> >NAME or part of a NAME?
> >
> Offhand, I don't see any explicit restriction on that in the RFCs, but
> what would be the value of adding the extra level(s) of indirection? I
> see only risks, since probably most DNS implementations wouldn't expect
> it and might handle it badly, and no benefits.
You're right that there's not much point to pointing directly to another
pointer. However, a variant case is certainly possible where a pointer
points to a name that contains another pointer. E.g. you could have the
following names in a packet:
foo.com.
bar.foo.com.
x.bar.foo.com.
These could be encoded as
foo.com.
bar.<pointer to foo.com>
x.<pointer to bar.foo.com>
The code necessary to handle this would *probably* handle the OP's case
properly, since expansion should be a simple recursive process.
--
Barry Margolin, barmar at alum.mit.edu
Arlington, MA
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