Failover without shared-network?

Ken Roberts ken at
Tue Jul 18 16:57:09 UTC 2006

On Tue, 2006-07-18 at 11:30, Simon Hobson wrote:
> Ken Roberts wrote:
> >I have a server version 3.0.3-r9 running on an up-to-date Gentoo system
> >which uses a 2.6 kernel.  It's an office setting with a set of Cisco
> >layer 3 switches using approximately 10 VLANs, which are separate
> >physical networks that map to subnet constructs in the dhcp
> >configuration file.  This configuration works exactly the way I want it
> >to.
> >
> >Now, the problem.  I need to set up failover.
> >
> >The documentation says I need a shared-network construct around
> >everything that is to have failover service.
> Where, I don't see that ?

Now suddenly I can't find it.  Admittedly I tried this over two months
ago, and maybe my updates have changed something.  I read the dhcpd
changelog and didn't see anything about this issue exactly, so I figured
it hadn't changed.  I was just going to get back into it and thought I'd
ask for help right away.

The first problem started with me trying to configure it, and the server
refused to start because the stuff wasn't inside a shared-network.  At
that point I discovered the documentation on that requirement, I thought
in the man page for dhcpd.conf(5) but it doesn't seem to be there now.

I can experiment after hours if necessary, but not right now. 
Preferrably I'll do anything I need to on the weekends instead, just so
I don't screw up a functional network.

> >   It further says that
> >inside a shared-network construct all the pools are jumbled together and
> >handed out randomly.  That's paraphrasing of course.
> Correct
> >In my understanding, shared-network means that several subnets are
> >sharing the same physical network.  This is not the case for me, but the
> >Cisco gear is using an ip helper-address that points to my DHCP server,
> >and forwards enough information that my clients get addresses that are
> >appropriate to the VLAN.
> >
> >The question here is, what is that shared-network construct going to do
> >to me?
> It would totally screw you up ! You do NOT want to do shared-network 
> if you don't have one.
> Simon

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