ISC DHCP server failover

sthaug at nethelp.no sthaug at nethelp.no
Sat Mar 20 03:43:41 CDT 2010


> With all due respect and acknowledgment of the tremendous contributions 
> of ISC and you yourself Mr. Hankins, I have to comment that failover in 
> isc-dhcp is broken by design because it requires the amount of 
> handholding and operator thinking in the event of a failure that you 
> explained to us at length is required. Failure needs to be handled 
> automatically and without any intervention at all, otherwise you might 
> as well not have it and I think most network operators would agree.

Note that this method of handling failover is inherent in the original
DHCP failover design. See

     http://tools.ietf.org/id/draft-ietf-dhc-failover-12.txt

Specifically, quoting from the above draft,

"While this technique works in some domains, having the only server to
which a DHCP client can communicate voluntarily shut itself down seems
like something worth avoiding.

The failover protocol will operate correctly while both servers are
unable to communicate, whether they are both running or not.  At some
point there may be resource contention, and if one of the servers is
actually down, then the operator can inform the operational server and
the operational server will be able to use all of the failed server's
resources."

I certainly cannot speak for "most network operators". However, I will
note that I have been aware of this behavior of the IDC DHCP server
as long as I have been running it in failover mode.

> I am certainly not prepared to develop proof of concept code or go the 
> full route of developing such a server myself, however, I belive firmly 
> that a failover implementation in dhcp could be designed as a 
> counterpoint to the current implementation that is reliable, simple, 
> scalable and requiring no special procedures once a 'break' occurs.

And which implements failover protocol in the IETF draft?

Steinar Haug, Nethelp consulting, sthaug at nethelp.no




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