TWC (AS11351) blocking all NTP?

John R. Levine johnl at
Mon Feb 3 20:29:21 UTC 2014

>> It seems thata hosts sending large amounts of NTP traffic over the
>> public Internet can be safely filtered if you don't already know that
>> it's one of the handful that's in the pools or another well
>> known NTP master.
> Speaking as one of the 3841 servers in the pool, I'm happy to be 
> described as a "handful," something my mother used to say, but I do feel 
> obligated to point out that it's a pretty big handful especially if you want 
> to be fiddling ACLs on an hourly basis which is pretty much what it takes.

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 

John Levine, johnl at, Primary Perpetrator of "The Internet for Dummies",
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