[DNSOP] Re: Working Group Last Call for draft-ietf-dnsop-cds-consistency

[Ondřej Caletka <[e-mail]>]

Hello,

sorry for chiming in a bit late but I find part of this proposal a bit 
harmful:

 > …the Parental Agent, knowing both the Child zone name and its NS 
hostnames, MUST ascertain that queries are made against all (reachable) 
nameservers listed in the Child's delegation from the Parent…

You cannot send queries to hostnames, you have to query an IP address. 
So you have to somehow convert each NS hostname into a set of IP addresses.

Normally people do this by asking the local recursive resolver. But with 
the spirit of this draft this does not seems to be reasonable thing to 
do because in a multi-signer scenario, each party can resolve the same 
hostname to a completely different set of IP addresses. Using local 
recursive resolver might thus bring completely random results based on 
which authoritative server will it query.

In fact, every single branch of the DNS tree can lead to resolving a 
hostname to a completely different set of IP addresses, including the 
possible inconsistency between the 13 hostnames of the root servers. 
Properly resolving a hostname into a set of all possible IP addresses 
would therefore require reimplementing a recursive resolver to make it 
follow not only one path but all the possible paths through the DNS 
tree. This would be extremely hard to implement and such a resolver 
would be extremely resource intensive to operate.

Then, suppose you get multiple IP addresses for a host name. Is it 
enough to ask one randomly selected address or does one have to query 
every single IP address the hostname resolves to? Again I see no 
guidance for this in the draft.

I think these are crucial questions influencing interoperability of 
implementations following this draft. I find it therefore harmful to 
just specify that you MUST query each NS hostname, without describing 
the details of how to do such a thing in a consistent and useful way.

Since Oli Schacher claims to have this draft already implemented, I 
wonder, what decisions did you take when implementing this? How exactly 
does your implementation works for hostname that resolve to inconsistent 
sets of IP addresses?

Also, appendix A1 describes an impossible failure scenario, considering 
that Section 6.2 of RFC 7344 says that:

 >  The Parental Agent MUST ensure that previous versions of the CDS/
 >  CDNSKEY RRset do not overwrite more recent versions.

--
Best regards,

Ondřej Caletka
RIPE NCC