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Sniperm4n
Asked: 2014-03-14 16:12:13 +0800 CST

ISC-DHCP-SERVER (primary/secondary) - Can Load Balancing Be Disabled?

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When I was hired at my company, I quickly determined that one of my highest priority projects would be to improve our ancient DNS/DHCP setup. It was running on an Ubuntu-based workstation-grade server that was more than 7 years old, and was in serious danger of keeling over. So, I started researching options for adding fault tolerance. I ended up building a standard Ubuntu Server 12.04.3 LTS 64-bit ISC DHCP failover cluster with a primary and secondary server, utilizing load balancing. The way things currently work, if my DHCP range consists of 54 IPs, the 2 servers split the IP pool evenly (27 each) while remaining in constant communication with one another. If one of the servers goes down for more than an hour without getting put into a partner-down state, my life then becomes hell.

I've since come to realize that the load balancing aspect is overly complex, and VERY unnecessary for our small shop. Unfortunately, I've been unable to find any documentation on how to create a simple primary/secondary relationship, whereby the secondary will take over all responsibilities in the event the primary experiences a failure (it would ideally function as a hotspare). Does this functionality exist within ISC-DHCP-SERVER v4.1.ESV-R4-0ubuntu5.6? If so, how in the world is it configured? I've seen mention of things such as "split 256" (as opposed to the "split 128" I'm currently using), but I can't find anything to definitively confirm this. If the convoluted load balancing feature is a requirement for fault tolerance, then so be it. Also, a quick note that I'm more of a Windows Admin than a Linux Admin, so please be gentle :P

Thanks, -Snipe

server

1 Answers

  1. https://kb.isc.org/article/AA-00502/0/A-Basic-Guide-to-Configuring-DHCP-Failover.html

    the first comment answers this i Think:

    [Michael McNally]: Re: Failover without load balancing2014-03-04 00:01 That's what the "split" or "hba" values are for -- you can read more about them in the dhcpd.conf man page.

    Setting a split value of 128 divides responsibility for the clients between the two failover partners. But if you want one partner to be principally responsible for all clients and the other partner to only grant leases if the client has been retrying for more than a certain number of seconds or if the peer is in partner-down state, you can set the split to 0 (secondary is chiefly responsible for answering) or 255 (primary is chiefly responsible for answering.)

    "split" and "hba" are mutually exclusive -- you can use one or the other but never both.

    You may also want to read about the "load balance max seconds" setting, which tells how long a client is expected to retry before the peer will answer even for clients for which it is not principally responsible.

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