Failover without shared-network?

Glenn Satchell Glenn.Satchell at
Wed Jul 19 11:49:29 UTC 2006

>Subject: Re: Failover without shared-network?
>From: Ken Roberts <ken at>
>To: dhcp-users <dhcp-users at>
>Date: Tue, 18 Jul 2006 11:57:09 -0500
>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.

I've run failover for nearly 5 years, and I don't ever remember seeing
a requirement fo rshared-network. In fact I have a failover running on
my home network and that certainly does not have a shared network.

Failover operates at the pool level, so you need to create a pool
within each subnet containing: range, deny dynamic bootp clients, and
the failover peer name. Everything else can be in the subnet or global

Here's an example from my home network:

subnet netmask {
  option routers;
  option subnet-mask;
  pool {
    failover peer "14subnet";
    deny dynamic bootp clients;

One tip for failover configuration. Use the "include" statement to
include the failover peer definitions in a separate file. That way the
main configuration fiule can be identical for both failover partners.
Edit on one system, then copy the file to the other to ensure they are
always identical.


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