DHCP Issue - Wyse WSM - Wyse Software - Dell Community

DHCP Issue

  • DHCP Issue

    Has anybody else noticed that when you reboot a zero client it will never resume its DHCP lease but rather it requests a brand new IP Address? Any idea why this might be. A normal PC when rebooted as long as its lease is still valid will request the same address again. The problem I have is that I have 25 or so terminals in a lab. If for some reason that lab gets rebooted during the day I now am taking 50 reservations up in a class C. Sometimes I don't have the available addresses for this and I then end up with users being unable to get on the network until either some of the original leases expire or I manually expire leases. I need some way to address this without just increasing the size of my network scopes.

    Tim B

  • Is it possible to lower the lease time on your DHCP server? I know in a VDI, I have lowered the lease time to 2 hours without any risk of newly attached clients or reboots to consume too many leases. I have not noticed your particular case though, but I'm still in the beginning stages of getting this all setup and working.

  • We did ultimately have to lower the lease time I was just hoping that there was a fix for this as it is clearly a problem. Even with relatively short lease times I still have the potential to need to reboot up to 100 R00L's at a time. Once I do that I am consuming 200 ip addresses for the duration of the previous lease.

  • DHCP release is controled by the DHCP server; there is no client side setting to quit the lease at shutdown automatically.
    You can add a shutdown script to your GPO that does an ipconfig / release, this should to the trick.

  • The previous statement isn't 100% true. The dhcp protocol calls for stations to send a DHCPRelease on proper shutdown (Mac's do this as well as most linux distributions) Windows has never done this. In windows 98 it was possible to make a registry edit that did this, this does not seem to be the case in Windows XP (at least that I have seen). I am still perplexed as to why the station doesn't simply re-take the same lease. Functionally it is not a problem for me anymore as I have just shortened the leases... It is just an annoyance at this point that I wish I could solve.

  • It turns out it has to do with the transactional model that DHCP employs. The "finite state machine" transaction model of DHCP allows a PC that has rebooted or come back online to start in the middle of the transaction by simply requesting the last IP address that it had. The zero clients are unable to do that as the machine obviously needs to have an IP address before windows starts meaning it cannot check to see what it's last IP address is. Bummer...

    FYI> more info on the subject.
    http://www.tcpipguide.com/free/t_DHC...ateMachine.htm