5 comments on “Server 2012 DHCP Failover – Reservation Issue

  1. We use reservations for all network infrastructure other than routers, and this has been such a huge pain since we upgraded to Server 2012.

    I don’t like having to turn off conflict detection, but it’s preferable to random devices going offline because their reservation gets hosed.

    Thanks for the information.

    • The one time we actually needed failover, we ran into this issue and it caused significant problems for us. The HA DHCP setup is a great move by Microsoft, but it needs some additional work before it can be relied on as designed.

      Until then, conflict detection will be turned off for us!

  2. Like Ben, we have had a challenging time with DHCP since we moved to 2012 several months ago. Random reservations getting messed up at random times, and have not been able to make any sense of it at all. We have found that the MAC address in the reservation gets randomly changed to the hex of the reservation’s IP address. Why? No idea. But it is very frustrating and has us on the brink of moving backwards to 2008 just for stability.

    Does anyone know why this is happening?

  3. I recently set up 2 dhcp servers failover relationship hoping to resolve bad_address issues as single dhcp was marking as bad_address my reserved ips frequently. What I’ve noticed was that when client with reserved ip was at 50% time of a lease and was requesting for a renewal by sending dhcp release packet server instantly was marking that ip as free to distribute. From now every client discovering was offered that ip even though mac mismatched the reserved one and after client requested for that offer server suddenly changed its mind by sending nack packet to say sorry it’s reserved for other mac address causing computers stuck in DORA state later getting into DORN state. That drives me bananas as later most clients have APIPA. Also when client roams around different APs and it’s reception is lost for a while it tries to renew lease and server pings the ip and having response from that ip automaticly blocks it and marks as bad address. I’m trying different way now. 2 dhcp servers with failover relation set as hot standby and no ip conflict detection at all. Plus applied a kb 2919393 that should stop issuing offers of reserved ip to clients with mismatched mac address.

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