DHCP failover setup different IP offering with 2 helper address

[Glenn Satchell]

Hi Alp

There's a rather long section in the dhcpd.conf man page. Scroll down to
the section "DHCP FAILOVER" and follow from there.

It's quite normal for the dhcp servers to offer different IP addresses.
The pool balancing splits the free IP addresses between the two servers,
so they offer an IP out of their portion of the free addresses. Unless
they've already seen that client before in which case they will offer a
previous address.

The dhcp clients should be able to cope with multiple offers, and will
select a suitable one, often the first received.

Make sure the dhcp servers have their time synchronised, most easily done
by running ntp.

regards,
-glenn

On Sun, June 28, 2015 10:33 pm, Alp Eren Kose wrote:
> Hello,
>
> We have setup a DHCP failover configuration, with Wireless LAN Controllers
> having multiple ip-helper-address statements. The controllers are Cisco
> and
> Aruba branded. As I understand it, Controllers relay DHCP discover
> messages
> to both DHCP servers, however sometimes we see different IP addresses are
> OFFERED for the same request by both DHCP servers. Is it the normal
> behavior?
>
> Could you also point some documentation that I can read to understand how
> exactly failover works in ISC DHCP version 4.2.8? Especially how multiple
> discovery and request packets are handled from multiple ip-helper address
> statements.
>
> Note: Please forgive me if it has been asked before or is really a basic
> question. I did have a quick look and did not come up with an answer, I
> wouldn't be posting without more search if it wasn't urgent.
>
> Thanks in advance.
> Alp
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