Failback causes lost lease

Gregory Sloop gregs at sloop.net
Thu Jun 25 19:47:59 UTC 2015



SM> In testing my dhcp failover, I pulled the ethernet cable on the primary
SM> server.

SM> The secondary server acknowleged renewal requests as expected.

SM> Then I plugged the cable back in. After both the primary and secondary
SM> had moved from communications-interrupted to normal, the secondary logs
SM> multiple dhcp requests from a client whose lease is owned by the primary
SM> server. The primary server does not log any of these but the last 
SM> request, reporting that "lease in transition state expired".

SM> Then the secondary server logs a DHCPDISCOVER from that client and 
SM> records it load balancing to the primary server.

SM> The primary server also sees the DHCPDISCOVER and offers a new lease 
SM> that is not the same number as the previous lease. This despite the old
SM> number not having been reassigned.

SM> The end result is that failback causes my clients to change their ip 
SM> address.

SM> Why does this happen and how can I prevent it?

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1) Logs would be good.
2) I think something with your config is broken. If I were to [wildly] guess, it's a physical/network layer issue.
3) I have a very small setup with 100+ clients, and it certainly doesn't work this way for me. 

There are some issues when a single server is up and in "communications interrupted" mode and you've got a tight IP pool and the leases were fairly evenly balanced against both servers. [I've posted, in the past, about an event that was kinda ugly for this client while running a 4.1 version [IIRC]. *However* those problems should be vastly less of a problem with 4.2+ - and you're not having an issue with communications interrupted anyway.

IIRC, you had a problem where the two servers wouldn't recover from CI to Normal like they should too. How did you solve that problem? Is it possible this is related? [I'm too lazy to go check old threads, but I _think_ it was you...my apologies if I'm wrong.]

-Greg
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