[LEAPSECS] Leap seconds ain't broken

[Michael Shields]

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.