[ntp:questions] Compensating for asymmetric delay on a per-peer/server basis?

detha detha at foad.co.za
Fri Sep 12 06:58:54 UTC 2014

On Thu, 11 Sep 2014 21:09:46 +0000, Rob wrote:

> Paul <tik-tok at bodosom.net> wrote:
>> On Thu, Sep 11, 2014 at 2:29 PM, William Unruh <unruh at invalid.ca> wrote:
>>> I doubt that NAT would add much assymetry
>> NAT is symmetric.  Otherwise it wouldn't work.  But I don't see how
>> that's part of anything at hand.
> I never claimed it is part of the asymmetry, I only mentioned it because
> usually you use a private IP range on a LAN, so when you are both on a LAN
> and on Internet you either have two different IP addresses (as I do) or
> you have NAT between an external address and your LAN range. The NAT is
> not causing asymmetry but it makes it more difficult to separate the
> internal from the external traffic.

That is, if you run ntpd on a directly internet-facing machine. In most
scenarios involving NAT, the NAT happens in a router/firewall/modem
appliance, not on the ntpd server itself.

Also, if/when IPv6 becomes more prevalent, all machines on the LAN will
hopefully have a public address.

You could specify a different offset based on /source/ address of the
query, or on incoming interface, but I am afraid that will open yet
another can of worms.


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