Watching performance on a DHCP Server

David W. Hankins David_Hankins at
Mon Feb 11 16:39:40 UTC 2008

On Fri, Feb 08, 2008 at 05:44:39PM -0600, Blake Hudson wrote:
> The pros of async are that I can spend much less on server hardware, the 
> cons being that I might lose 5 seconds (default commit time for ext3) of 
> leases (single digits?) if my server were to freeze (again making the 
> same assumptions about hardware failure).

It's impossible to say what will go on in those 5 seconds; it could
have been only one client, it could have been _all of them_.  These
days if an ethernet switch gets power cycled, all the clients will
renew early as soon as they get link back.  It's impossible to say
what events will "coincidentally" lead up to a failure.

Once beyond the failure, you get into all sorts of client behaviour
resonance; clients start DECLINEing leases that are already in use,
if they are capable of that, and once a lease is DECLINEd it is never
used again unless reset by the operator or no other leases are

> I'd love to see this available as an option left up to the server 
> administrator. I'll take a gander at the source next week and see 
> exactly what it might take. Any changes I make will probably not be as 
> useful as I'd prefer to stick with the src rpm provided by my 
> distribution (Fedora), which is currently 3.0.x based.

I don't think the sources in question have changed much at all between
3.0.x and 4.1.x, but if you could draw your diff against 4.1.0a1, that
would be appreciated.

Ash bugud-gul durbatuluk agh burzum-ishi krimpatul.
Why settle for the lesser evil?
David W. Hankins	"If you don't do it right the first time,
Software Engineer		     you'll just have to do it again."
Internet Systems Consortium, Inc.		-- Jack T. Hankins

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