[ntp:questions] Three NTP servers, one strange IP-address in 'refid'

Terje Mathisen terje.mathisen at tmsw.no
Wed Apr 2 12:31:21 UTC 2014

Sander Smeenk wrote:
> Quoting Miroslav Lichvar (mlichvar at redhat.com):
>>>> I guess it could also be a IPv6 ref mangling issue?
>>> That could well be. We use IPv6 where we can.
>> For IPv6 addresses the refid is defined as first 4 bytes of the MD5
>> sum of the address. With 2001:7b8:3:32:213:136:0:252 (tt52.ripe.net)
>> that is 0xac023551, or in the quad-dotted notation.
> Miroslav, you're right. This is it. Thanks.
> I've changed everything over to IPv4 by not using hostnames anywhere.
> The IP is gone.
> I consider this a bug.
You can consider it whatever you like, but when something is working 
both as designed and as documented, it is by definition a feature. :-)

If you want to "solve" this problem then you would have to make a 
non-backwards compatible modification to the ntp network packet format, 
extending the reference field from 32 to 128 or even more bits.

The alternative is to add another optional field at the end of each 
packet, with the client setting it to the maximum acceptable size and 
the server filling it up.


- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"

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