DHCP Failover - initial Configuration

Philippe Maechler plcmaechler at gmail.com
Fri Aug 10 05:12:08 UTC 2018

On Thu, 9 Aug 2018 at 18:32, Simon Hobson <dhcp1 at thehobsons.co.uk> wrote:

> perl-list <perl-list at network1.net> wrote:
> > Even that doesn't guarantee anything.  Clients can and do still suggest
> and receive a different lease length.  Its really not often, but I have
> seen it.  For example, some versions of windows will initially request an
> hour lease followed by a full lease length (ie: what you have configured in
> your directives) at renewal time.  This would be when you have longer than
> an hour lease lengths configured.
Yes, client cant and do ask for shorter or longer lease times, but the
server declines that and hands out only leases with a lengt of 1h. The only
exception is for leases wo fall into the dhcp-cache-threshold option. They
get a "shorter" lease time offered.

> The server should never offer a lease shorter than min-lease-time, or
> longer than max-lease-time - except when failover is/has happened and MCLT
> is in effect. A client could choose to not use the full lease length, but
> it cannot (unless broken) use the address for longer than the lease time
> offered.

We once had a broken client who refused the lease offered. The client did
the DORA sequence, declined the lease and startet again with a DORA
sequence and so on. Except from that we never faced an issue with default-,
min- and max-lease time set to 3600s
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