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

Dave Hart davehart at gmail.com
Sun Feb 15 16:49:58 UTC 2009


On Feb 15, 4:13 pm, ma... at ntp.org (Danny Mayer) wrote:
> Dave Hart wrote:
> > On Feb 13, 2:50 am, ma... at ntp.org (Danny Mayer) wrote:
> >> I've had only my list of things to do to use only one refid per system
> >> rather than based on the IP based being used.
>
> > This certainly seems like a winning idea in terms of loop detection.
> > If you do something like this, it would be nice if without extra
> > configuration RFC1918 addresses would tend to not be used as refids
> > (like unless the only unicast IPv4 address available is RFC1918.
>
> I fail to see what RFC1918 addresses have to do with it. There's always
> likely to be a mixture of public/private addresses in an ntp
> configuration and I see no point in preferring one over the other.

RFC1918 addresses are of course not globally unique, so are
particularly ill-suited to a reference ID used for loop detection.

> In
> addition this ignores the IPv6 addresses and it is intended to tackle
> that issue as well. It would be better if these were just a generated
> 32-bit random number created at startup which is kept for the lifetime
> of the server.

Why play roulette if you have a globally unique IPv4 address to use as
a refid?  Since IPv6 addresses are hashed down to 32 bits if used as a
refid, again, IPv4 global addresses if available are better unique
identifiers.

Cheers,
Dave hart




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