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

Martin Burnicki martin.burnicki at meinberg.de
Fri Apr 4 07:51:57 UTC 2014

Rob wrote:
> Harlan Stenn <stenn at ntp.org> wrote:
>> Martin Burnicki writes:
>>> Harlan Stenn schrieb:
>>>> Sander Smeenk writes:
>>>>> Quoting Miroslav Lichvar (mlichvar at redhat.com):
>>>>>> 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 consider this a bug.
>>>> As do we all.  And we can fix it as soon as a decent solution appears.
>>> Maybe just print the refid as hex bytes instead of dotted quads unless
>>> it's interpreted as string?
>> Printing 32 bits of information in dotted-quad format takes 15
>> characters.
>> Printing 128 bits of information in base64 takes 22 characters.

I didn't mean to break the protocol by extending a 32 bit field to 128 bit.

I just meant to print the 32 bit refid field from the NTP packets in hex 
instead of dotted quads, unless they are interpreted as ASCII 
characters, e.g. "AC100E19" instead of "".

This would prevent many people from interpreting this as an IPv4 
address. ;-)

Of course a better solution would be to be able to distinguish it the 32 
bit number is a full IPv4 address, or only a 4 byte hash of an IPv6 
address, and display an IPv4 address as dotted quad, and a hash as hex 
number. I don't know if a tool like ntpq can determine what the refid 
actually represents.

> The problem is not the printing!
> Before 128 bits of information can be printed at all, the protocol
> has to be modified to transfer the bits in the datagrams.
> The use of a 32-bit field for the refid is as hardwired in the protocol
> as 32-bit addresses are in IPv4.
> It is not realistic to change this.  What could be changed is the use
> of the 32 bits when IPv6 is in use (as I proposed), and the printing
> of the 32 bits in that case.

Sorry, I don't remember your proposal. Do you have a pointer to it?

Martin Burnicki

Meinberg Funkuhren
Bad Pyrmont

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