Re: [Ntp] Comments on draft-langer-ntp-nts-for-ptp

On 8 Mar 2021, at 12:14, Miroslav Lichvar wrote:

> On Mon, Mar 08, 2021 at 11:43:29AM +0100, Heiko Gerstung wrote:
>> As far as I can see, up until this point the mechanism can be very 
>> similar to NTS4NTP. We most probably need a different cookie format, 
>> but the rest should be OK. Once we did 1 + 2, the unicast master will 
>> start the PTP packet transmission to the authenticated (via the 
>> cookie) PTP client. The client will also start sending Delay Req 
>> packets and requires the GM to respond with unicast delay responses.
>>
>> During this packet transmission phase I propose to use the S2C to 
>> secure the packets from the GM to the client (ANNOUNCE, SYNC, 
>> DELAY_RESP) and the C2S key to secure the packets from the NTS/PTP 
>> client to the GM (i.e. DELAY_REQ).
>
> I don't think it makes sense to use NTS cookies in PTP, even if you
> limit the NTS support to the unicast mode. The main point of the
> cookies is to avoid having client-specific state on the server. That's
> not possible in PTP as announce and sync messages are not responses to
> requests. They are sent at their own interval, which can be different
> from the delay request interval.
>
> In PTP there has to be some client-specific state and the clients need
> to be authenticated. Very different from NTS-for-NTP.

I agree with Miroslav. There is already state information defined in the 
IEEE 1588-2019 version in the context of the Authentication TLV. It 
should be possible to use them also for this purpose. This would make 
things easier compared to offload state information via cookies to the 
slaves and would minimize computational for the master.

>
> -- 
> Miroslav Lichvar
>
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