dhcp server IP pool monitoring

Joseph Bernard JHB at clemson.edu
Fri Mar 14 20:15:11 UTC 2014

We use OMAPI to read the lease information in memory since there's a delay with what's in the lease file and what's current.  We use an old version (3.0.5), so that might have been fixed since then.

Joseph B.

On Mar 14, 2014, at 3:27 PM, John Wobus <jw354 at cornell.edu>

> If you refer to the delay-commit function, it is
> the responses to the client that are delayed so
> that committing disk writes can be batched,
> so the disk is still up to date by the
> time the client gets the lease info,
> i.e., according to the spec.
> There wouldn't be any few-second delay.
> I trust Linux a bit less though:
> interactively, I've closed a file with vi, then
> ran a program that appeared to miss the change.
> Would vi(m) manage to exit without any synch
> happening?  (I've never noticed anything
> equivalent with dhcpd lease file handling.)
> We do parse the lease file and compare with
> an external description of our pools to monitor.
> The "pool-label" idea is very interesting, but
> not enough for me to re-implement right now.
> A "check-leasefile" program that could efficiently
> output current leases in trivial-to-parse format
> would be a neat addition to the isc dhcp bundle.
> If it could read the config and do all the pool
> assembly/monitoring work, that would be neat
> as well.
> John Wobus
> Cornell University IT
> On Mar 13, 2014, at 5:54 AM, Simon Hobson wrote:
>> "Capriccio, Peter" <peter.capriccio at hp.com> wrote:
>>> All of the solutions that parse the lease file can never be 100% accurate because the real "stuff" is taking place in memory, is it not?
>> No, for any RFC compliant package, the leases file (or equivalent) on disk will accurately reflect any leases before they are offered to the client. This is certainly the case with the ISC DHCP server - all lease information is written to the leases file and synced to disk before the lease is offered to the client*
>> Worst case is that the lease file lags in-memory information by a few seconds.
>> * Though I believe the current version has a config option to delay this a little for performance ?
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