[ntp:questions] NTP over redundant peer links, undetected loops

Danny Mayer mayer at ntp.org
Mon Feb 16 03:48:20 UTC 2009

Ryan Malayter wrote:
> On Sun, Feb 15, 2009 at 12:23 PM, Danny Mayer <mayer at ntp.org> wrote:
>> Because I want to get away from the notion that these are meant to be IP
>> addresses. In addition in an IPv6-only environment that wouldn't work
>> either. Why create work when it's unnecessary just to find a valid IP
>> address? In addition with anycast addresses are not globally unique. The
>> chances that you will create a non-unique random number within a network
>> is extremely low.
> It depends on the size of the network. The chances of a duplicate
> 32-bit number on a network including 65000 hosts is about 40%. The NTP
> Pool network, which comprises at least 10^6 hosts, for example, would
> have collision probability very close to 1.

You need to understand what loop prevention is. In any case I very much
doubt that there are a million hosts in the pool. Loop prevention won't
be affected by choosing no more than say 10 hosts in the pool. That's
the maximum number that the pool configuration option selects. In a
network of 65000 hosts you will not have more than three or four
selected at the same stratum level.  If they are not at the same level
then you don't have to worry about loop detection. You are reading far
too much into the statistics of something where they don't really apply.


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