[ntp:questions] ntp server with two default routes misbehaving after upgrade

Jochen Bern Jochen.Bern at LINworks.de
Tue Apr 22 10:42:58 UTC 2014

On 22.04.2014 11:45, questions-request at lists.ntp.org digested:
> From: Caecilius <nospam at spamless.invalid>
> 1. tcpdump shows that the packet-level behaviour is the same for ntp
> 4.2.4p4 and 4.2.6p2. Namely packets to a given peer switch from one
> source IP to the other approximately every 10 minutes.
> So the packet-level behaviour hasn't changed between NTP versions, but
> what has changed is that 4.2.4p4 didn't seem to care wheras 4.2.6p2
> resets the peer when this happens.


a) Different OSes have different default behaviors when there are
several fully equivalent source IPs (including the routes marking them
as suitable for the target IP in question) to use. It's been a while,
but IIRC Linux is *not* prone to switching them under your feet. (More
precisely, what I remember is: SunOS uses the first to have been set up,
Linux the last, and *BSD round-robins.) Your machine flip-flopping
instead *might* indicate some problem that the newer ntpd merely made
more visible.

b) Assuming that both the flip-flopping and ntpd choking on it have good
reasons you cannot or should not ignore, you might want to do what EBGP
peers do - set up host routes that nail down which ISP connection (and,
supposedly, which source IP) will be used for which peer. (Of course,
EBGP and other EGPs do that because they need the peering to work
*before* they receive information from the peers and populate the local
routing tables with it.)

								J. Bern
*NEU* - NEC IT-Infrastruktur-Produkte im <http://www.linworks-shop.de/>:
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Jochen Bern, Systemingenieur --- LINworks GmbH <http://www.LINworks.de/>
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