DHCP failover setup different IP offering with 2 helper address

[Gero Palacio]

I need to correct myself. I did not meant the "mclt", I meant "*load
balance max secs*" option in the DPCH servers, sorry about that.

It is the expected behavior when the "sec" field in the DHCP client's
message is grater than the "*load balance max seconds*" defined in the
primary DHCP server. Or if the DHCP server are *not* in normal state. If
that's not the case (both servers in normal state and "sec" < "*load
balance max seconds*") both servers will receive the DHCP DISCOVERY message
but only one of them will reply back with an offer


>From *man dhcpd:*

*load-balance-max-secs integer examine*

Indicates the maximum value for the secs field in a client request before
load balancing is bypassed.


Cheers.

On Sun, Jun 28, 2015 at 3:04 PM, Gero Palacio <gero.palacio at gmail.com>
wrote:

> Hi Alp,
>
> 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?
>
>
> It is the expected behavior when the "sec" field in the DHCP client's
> message is grater than the "mclt" defined in the primary DHCP server. Or if
> the DHCP server are *not* in normal state. If that's not the case (both
> servers in normal state and "sec" < "mclt") both servers will receive the
> DHCP DISCOVERY message but only one of them will reply back with an offer.
> There's a thread describing a similar problem I had in this mail list,
> subject "DHCP Relay agent not forwarding messages to the client" first
> message from June 15.
>
> 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.
>
>
> You can check out this link DHCP Failover Protocol Draft IEFT
> <https://tools.ietf.org/html/draft-ietf-dhc-failover-12%20and> and this DHC
> Load Balancing Algorithm RFC 3074 <https://tools.ietf.org/html/rfc3074>.
> Always keep in mind this tip which I got from another thread in this mail
> list:
>
> The split *does not* determine the share of the pool. The pool is
>>  *always* balanced 50/50. The split value determines which peer will
>>  respond to the client based on the hashed value of the client
>>  identifier (MAC address).
>
>
>
> Hope this helps!
> Gero.
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.isc.org/pipermail/dhcp-users/attachments/20150628/c06cc539/attachment.html>