[LEAPSECS] Leap seconds ain't broken

[Martin Burnicki]

Michael Shields via LEAPSECS wrote:
> On Wed, Jan 4, 2017 at 1:46 AM, Martin Burnicki
> <martin.burnicki at burnicki.net> wrote:
>> I agree it would be good to implement this in an extension field, but
>> generally care should be taken not to break compatibility. I mean, how
>> do existing clients act if they receive a packet with unknown extension
>> field? Do they just ignore it, or do they just drop and ignore the whole
>> packet?
> 
> Another problem is that many ISPs are now filtering port 123 to
> packets with a specific, limited range of packet sizes.  Adding any
> extension fields can cause the NTP replies to be blocked entirely.

Ouch. Never heard about that.

But this may also mean that today's NTP service wouldn't work correctly
if you tried to use authentication. So this sounds like a broken
configuration at the ISP side.

Martin