Subject: Re: [TICTOC] IPv6 Router Advertisement Option for NTP Server Configuration

From: Dave Hart <[email-masked]>
Date: Fri, 23 Dec 2011 05:57:59 +0000

I have feedback that is generic to both autoconfiguration approaches
to distributing NTP configuration information -- RA as well as DHCPv6.
 Regardless of means, I'm suspicious of standardizing a way to
distribute multicast NTP server addresses without also standardizing
distribution of NTP symmetric authentication parameters needed to
secure broadcast/multicast NTP.  If providing such authentication
parameters (key number/id, digest algorithm, and shared secret) is
deemed too cumbersome, I suggest removing support for distributing
multicast NTP server information is preferable to providing means
which enable only ill-advised configurations that blindly accept
unauthenticated multicast NTP service.

Similarly, I would prefer to see broader support for other NTP
configurations.  If NTP symmetric authentication parameters are
provided for, NTP's manycast mode should be configurable as well.
Clients solicit manycast servers via authenticated multicast NTP mode
3 (client) requests destined to a multicast group address.  Manycast
servers respond via unicast mode 4 (server) responses, which triggers
manycast clients to spin authenticated unicast associations.  The
prime advantage over multicast service is the unicast operation with
discovered servers, which allows ongoing round-trip delay measurement
as compared to one-time multicast delay calibration at ntpd startup.
In short, manycast operation provides the automatic server discovery
benefit of multicast NTP without the degraded quality of time service
inherent in a one-to-many multicast/broadcast NTP configuration.

Cheers,
Dave Hart