Re: [DNSOP] DNS cookies and multi-vendor anycast incompatibility

> On 21 Jun 2018, at 12:25 am, Petr Špaček <petr.spacek@nic.cz> wrote:
> 
> On 20.6.2018 16:10, Paul Wouters wrote:
>> On Wed, 20 Jun 2018, Petr Špaček wrote:
>> 
>>> it seems that current specification of DNS cookies in RFC 7873 is not
>>> detailed enough to allow deployment of DNS cookies in multi-vendor
>>> anycast setup, i.e. a setup where one IP address is backed by multiple
>>> DNS servers.
>>> 
>>> The problem is lack of standardized algorithm to generate server
>>> cookie from a shared secret. In practice, even if users manually
>>> configure the same shared secret, Knot DNS and BIND will use diffrent
>>> algorithm to generate server cookie and as consequence these two
>>> cannot reliably back the same IP address and have DNS cookies enabled.
>>> 
>>> One of root server operators told me that they are not going to enable
>>> DNS cookies until it can work with multi-vendor anycast, and I think
>>> this is very reasonable position.
>>> 
>>> So, vendors, would you be willing to standardize on small number of
>>> server cookie algorithms to enable multi-vendor deployments?
>> 
>> I think this is a good idea but there are already two examples in RFC
>> 7873 for cookie generation. Is there a problem with those examples, or
>> is there only a lack of options in the implementation to configure
>> these? If the latter, than no new IETF work would be needed.
> 
> These are mere examples and not specifications with all the details
> necessary for reliable interoperability.
> E.g. when a cookie is "old" according to B.2.?

I really depends on the algorithm being used.

> E.g. are there privacy considerations with plain HMAC vs. encryption?

Not the way AES is being used. 

> Besides this, BIND defaults to AES-based algorithm which is not
> specified in the RFC and Knot DNS has its own because developers
> considered the BIND's approch overkill.

What does it matter what the default algorithm is.  Unless you are
running a anycast cluster IT DOES NOT MATTER.  If you are running
a anycast cluster you just needs to make sure all the server are set
up the same way.

> If we decide to standardize we need to find a reasonable algorihm and
> standardize all its variables to make it work without run-time
> synchronization (posssibly except key rotation but it can be done
> avoided as well).

BIND implemented 3 algorithms.  All three were similar.  The only
difference was how the hash is generated.  The hmac-sha1 and hmac-sha256-8
take identical inputs.  AES is slightly different because it is AES.

> This message is for other DNS vendors to see if there is an interest in
> standardizing something we can all share and operators use in practice.
> 
> -- 
> Petr Špaček  @  CZ.NIC
> 
> _______________________________________________
> DNSOP mailing list
> DNSOP@ietf.org
> https://www.ietf.org/mailman/listinfo/dnsop

-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742              INTERNET: marka@isc.org