DHCP code in 2.0.4+

Karl Auer kauer at biplane.com.au
Mon Jun 8 02:55:13 CEST 2009

On Sun, 2009-06-07 at 22:25 +0200, Alan DeKok wrote:
> Karl Auer wrote:
> > DHCP failover and load-balancing are not simple *at all*.
>   As evidenced by the fact that the ISC fail-over protocol is horrible,
> and the implementation is almost as bad.

Oh, I'm 100% with you on that.

>   Oh, and the server is O(N^2) in the number of leases.  Why?  Well...
> they don't use fancy concepts like "dynamically resizable hash tables".

True, but that's ISC's implementation. I use Nominum's DCS, which starts
in seconds regardless of the number of leases, largely because it has a
database backend (but not distributed or HA - highspeed, local and
dedicated) and which is completely dynamically configurable. Nothing
short of upgrading the server requires it to be stopped. And with one
major exception (which was a *bug*), failover as implemented by Nominum
has never, ever let us down. Let's not confuse the protocol with the

>   It's really not that hard.  Database books describe replication
> protocols.  They look very different from the DHCP fail-over protocol.

Though to be fair, database replication is *not* solving the same
problem as failover is. Failover allows independent entities to maintain
the same view of the data, and a view with severe constraints. The real
mistakes were made defining DHCP itself, but for the time they did an OK

>   And for most enterprise sites, you *don't* need a fail-over protocol.
>  Really.

Well... if they have a HA arrangement for DHCP such as that described
here recently, maybe not. Otherwise we'll have to disagree on that.

Regards, K.

Karl Auer (kauer at biplane.com.au)                   +61-2-64957160 (h)
http://www.biplane.com.au/~kauer/                  +61-428-957160 (mob)

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