DHCP server failover: advise is needed

Dima Veselov kab00m at lich.phys.spbu.ru
Fri Nov 22 17:49:31 UTC 2019

On 22.11.2019 20:00, Valeri Galtsev wrote:

I had been in same situation as you described, my advice may be handy.

> Could someone point to description of working DHCP failover configuration?

I used https://kb.isc.org/docs/aa-00502 as an instruction.

> I do not want to make two independent DHCP servers handling half of the 
> pool each. We are not that rich as far as IP space is concerned.

> I am not married to ISC DHCP server, so any one I can run on FreeBSD 
> will do, because:
> <rant>
> My current configuration is something that was gradually migrated and/or 
> adjusted through several generations of systems, and server versions 
> over the years. It works. When I tried to incorporate what I need for 
> failover following ISC documentation, and some people's guides, I 
> discovered, I need more sophisticated structure of sections and 
> subsections, which I figured out finally. But the annoying part was: in 
> ISC documentation there is no general stricture of which section can 
> appear inside which; like:

Basically, ISC DHCPD allow described structures and nothing more. Being 
on your side I had to do some work like moving static hosts in main 
config and reorganize subnets. This seemed noisy but appeared quite 
easy. For detailed advice we need to see your config or questionable 
parts of it.

> So, I am not married to ISC DHCP server, we didn't get along now as far 
> as my use of documentation is concerned. Anything that works - with  > failover! - on FreeBSD will be great.

I can email you my own working configuration. General advice - try to 
make configuration as plain as it might be. If you have working subnets 
with working pools you just add failover peer and it start working.

Dima Veselov
Physics R&D Establishment of Saint-Petersburg University

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