[ksk-change] How to tell which trust anchors are present at a DNS resolver.

[Wessels, Duane]

> On Mar 24, 2015, at 4:03 PM, Michael StJohns <msj at nthpermutation.com> wrote:
> 
> One of the discussions we've been having about 5011 roll overs is that there's no way to tell whether or not they are "taking" because there's no way to check the resolvers externally.
> 
> I was looking at various possibilities including locally significant RRs that could be queried to , but nothing clicked.
> 
> After a beer with Scott Rose - we came up with the following convention:
> 
> Querying a server with QNAME="." and QTYPE="DS" and with no recursion, gets you a set of DS records that represent the trust anchors for that server for the root.
> 
> This would have to be implemented, but given that I think it may take 2 years to get the rollover done, that may not be a problem.
> 
> 
> Comments on this approach?  (Note comments of "this won't work because its too late" are understood and ignored).  What we;re looking for are comments on whether the convention has bad side effects or would be difficult to implement correctly.


I think its reasonable enough to discuss.  Negative side effects that I can think of:

- Special case in recursive resolver code for this name/type

- I'd expect to see "IN/./DS" queries become used in DDoS attacks

- Some (incorrect) implementations would almost certainly forward these to the roots.

- Doesn't work for stubs.

I'm not sure it solves the problem of being able to check resolvers externally.  You would rely on them to have an open resolver path or use some other tricks.

Perhaps worth considering alternative proposals such as some kind of CHAOS TXT query?

Or an EDNS extension whereby a client can transmit its trust anchor/DS keytag(s) along with a DNSKEY query?  This could work for all zones, not just
root, but I suppose it assumes the validator knows the DS before it makes the DNSKEY query (top-down vs bottom-up).

DW