[ntp:questions] Bad NTP servers jeopardizing the pool.ntp.org initiative

Danny Mayer mayer at ntp.isc.org
Mon Apr 2 03:14:37 UTC 2007

Harlan Stenn wrote:
>>>> In article <460FAE61.40804 at ntp.isc.org>, mayer at ntp.isc.org (Danny Mayer) writes:
> P>  As you might have seen elsewhere I do agree that this is only a good
> P> idea under well defined circumstances, and I would now add that it is
> P> difficult to ascertain up-front whether these conditions are met (i.e.
> P> whether it would be desirable for a particular NTP server on a dynamic IP
> P> address to be admitted to the pool).
> Danny> There are *no* circumstances where this is a good idea. You *cannot*
> Danny> make use of a server that is constantly moving IP address. Even fixed
> Danny> IP addresses can be problematic in this environment since the clients
> Danny> don't requery for addresses after they come up and if someone decides
> Danny> to move the server elsewhere, they will never know about it.
> Danny, while you are right that one cannot expect to get useful NTP service
> from a moving IP address you are flat out wrong that all DHCP-assigned
> addresses fall in to this category.

To clarify one thing, an IP address that is fixed for a given server is
fixed even if it's assigned by DHCP. How it gets assigned is a detail.
Whether or not that server keeps the same address is crucial.

> I think you have tunnel-vision in this case, and are being blind to some
> cases where obvious/known counter-examples exist.

I don't think so. Please provide counter-examples.

> P> Please remember that I started this suggestion in the context of a
> P> discussion of code being added to ntpd that re-resolves server addresses
> P> in case of non-reachability. Such code, _if deployed on a critical mass
> P> of clients_ (i.e. optimistically, not for a good few years) would address
> P> your concern (while not completely removing it).
> Danny> We are not the only provider of NTP Clients or for that matter
> Danny> servers and unless they also make changes to also do this and have
> Danny> everyone upgrade the problem will remain. For most people/admins this
> Danny> is a set and forget item when they set up a system.
> Danny, from my POV you didn't even address Per's point, and his point seems
> perfectly valid to me.

Which point would that be? Having NTP servers with varying addresses is
a good idea? Even when the above mentioned code change happens, and that
will take quite a lot of work and will cause me to make a lot of changes
to the code and even longer to get it just right, it still won't deal
with the issues I've raised including the fact that there are a lot of
other NTP clients out there. We already have cases of people hardcoding
IP addresses of NTP servers without unauthorization of the owner of the
NTP server.


More information about the questions mailing list