DHCP Failover - initial Configuration

Philippe Maechler plcmaechler at gmail.com
Thu Aug 9 06:15:25 UTC 2018

Hello Simon, hello list

On Wed, 8 Aug 2018 at 19:24, Simon Hobson <dhcp1 at thehobsons.co.uk> wrote:

> > Server restarts
> > Currently we restart the service every 5minutes if something changed.
> When we go for failover, we should reload server one and if it synced to
> his partner, we can reload the server two. How does server two know, that
> the server one is up to date and everything is synced?
> After a restart it will take time for the servers to resync. You'll need
> to adapt your management system to hold off on restarts. Hopefully someone
> more familiar with failover will be along soon with more details, but from
> things said on here, there are some cases where the servers can take a
> while before they get back to fully normal operation.

Yes, I'm already testing a way for checking the server state before a
reload. The current idea is, that our reload script first checks via omapi
the failover-state from the other server. If the server is in ready and in
sync, we do the reload. otherwise we wait another few minutes. Since we
already rely on omapi for other things, this shouldn't be much magic :)

Something else you mentioned, mlct. On of our access system is doing
something like dhcp-snooping/dhcp-aging. When a client successfuly logs on
with a DORA sequence, the clients mac address is allowed to communicate for
a given time. unfortunately this time is hardcoded in the access system and
not learnt from the DORA sequence. If we have a lease time of 7200s but an
mlct of 3600, clients would first get a lease time of 1h and on a
Request/Ackownlede a lease time of 2h. Would that work if we set
mlct==lease-time? What are the benedits and drawbacks from such a
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