TWC (AS11351) blocking all NTP?

Joe Greco jgreco at
Mon Feb 3 17:29:21 UTC 2014

> >> I was thinking that the servers on any particular network are a small set of exceptions to a general rule to rate limit outgoing NTP traffic.
> >
> > allows any NTP operator to opt-in to receive NTP traffic should their clock be available and accurate.
> I believe you, but I don't believe that the set of servers changes 
> so rapidly that it is beyond the ability of network operators to handle 
> the ones on their own networks as a special case.

There's a bootstrap issue here.  I'm guessing that you may be picturing
a scenario where a network operator simply queries to obtain the list of servers and special-cases their own.  However, I believe that
the system won't add NTP servers that appear to be nonresponsive to the
list (bootstrap paradox), and in any case the list of returned servers 
is quite large and a response basically picks a few random servers, so 
it is quite difficult to know what servers are on your network in an 
automated fashion.

... JG
Joe Greco - Network Services - Milwaukee, WI -
"We call it the 'one bite at the apple' rule. Give me one chance [and] then I
won't contact you again." - Direct Marketing Ass'n position on e-mail spam(CNN)
With 24 million small businesses in the US alone, that's way too many apples.

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