On Sun, Oct 24, 2010 at 8:34 AM, Brandon Kim <brandon....@brandontek.com> wrote:
>
> Hey guys:
>
> I wanted to open up this question regarding NTP server. I recalled someone 
> had created a posting of this quite awhile back.
> >From a service provider/ISP standpoint,  does anyone think that having a 
> >local NTP server is really necessary?
>
> I've asked some of my fellow engineers at work and many of them gives me the 
> same response, "Can't we just use free ones out on the internet?"

Depends on how much you trust other people.
NTP can potentially be used as a DoS vector by your upstream clocks,
if you're not running your own.

I've seen 50,000 servers panic in the blink of an eye when the NTP source
issued a leap second, and the kernel wasn't patched to handle it properly;
and that's a forward leap second.  Nobody's tested reverse leap seconds
yet; who knows what would happen to your hosts if your upstream NTP
servers decided to issue a reverse leap second towards you?  Granted, if
you choose enough diverse upstream clocks, that becomes more difficult
for someone to exploit; but it's not impossible, and you can't count on
keeping your upstream clock sources secret, given the bidirectional
communication that can take place between NTP servers.

*shrug*  It's cheap enough to run your own clock sources, once you're
above a certain size, and it's one less potential attack vector from the
outside; why wouldn't you want to secure your edge against it?

Matt

Reply via email to