Re: [TICTOC] Mirja Kühlewind's Discuss on draft-ietf-tictoc-multi-path-synchronization-05: (with DISCUSS and COMMENT)

[Stewart Bryant <[e-mail]>]

On 22/09/2016 12:52, Mirja Kuehlewind wrote:
>
> ----------------------------------------------------------------------
> DISCUSS:
> ----------------------------------------------------------------------
>
> "Each NTP clock has a set of N IP addresses. The assumption is that
>        the server information, including its multiple IP addresses is
>        known to the NTP clients."
>
> A protocol specification should not make this assumption but describe a
> mechanism how a client gets to know about these IP addresses.

The base NTP protocol gets the time server addresses by configuration, 
and thus
the assumption seems reasonable.

There is something of a chicken and egg problem here since the IP
address of the time servers needs to be securely known, but to run a 
security
protocol needs knowledge of the time. This observation may well point to a
security issue with the popular use of anycast domain names in NTP
configuration since it is difficult to see how you authenticate DNS without
prior access to time to validate a certificate from the DNS server.

You might encourage the IETF to look at this conundrum, and indeed the IOT
folks would like a solution, but I don't think you can burden this draft 
with
solving the problem.

Regards

Stewart