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Re: DNS contamination

  • From: Alex.Bligh
  • Date: Fri Jan 24 07:35:29 1997

> > Ignoring additional records works pretty well for me.
> This is harder than it looks.  Sometimes the glue A RRs are the only ones
> you can get -- you need them in order to ask questions in the domain they
> are in, so without them you have infinite regress.

This might be naive but: AFAIK the only time you *need* glue A RRs rather
than normal A RRs is when you are looking for a namserver whose name
is within the zone,

i.e. within .com

foo		NS	A
foo		NS	A
foo		NS

the top two are correct glues, and the bottom one doesn't need one.

The danger is that the A record is incorrect, or that someone has
stuck it in unnecessarilly, like (in .com)

foo		NS	A

So, why not tag such glue records when the go in the cache as
suspect. Then when you first refer to them, query them for their
own A record. IE in the top example above, when the A RR for is just about to be pulled out the cache, it is has
some marking as "suspect", so a direct query for an A RR for is made. This first tries (which we think
is We do this with norecurse set. If the glue
record is right, it returns and it goes into the cache
OK. If the glue record is wrong, the query fails and we try
the secondaries. This one might be wrong too, in which case
we continue until we get a correct one (here

I spent a few (fruitless) hours trying to work out why 1/2 the
internet had incorrect A records for and in the end
concluded (as I say, perhaps niavely) that something like
the above would solve the problem.

Alex Bligh
Xara Networks

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