Announcement

Collapse
No announcement yet.

Static to DHCP Adressing Planning

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • Static to DHCP Adressing Planning

    My organization is about to embark on a journey into the world of DHCP. Currently we have a static enviroment with around 650 hosts. Our main application has recently allowed support for DHCP based clients using a hostnames/DNS setup.

    In our enviroment we have 13 VLANS that we support. We plan to setup a DHCP scope for each VLAN to support up to 200 DHCP hosts on our 6509 Core switch.

    Is there anyway to turn on DHCP on each VLAN while we still have static hosts, but yet prevent ip address conflicts?

    As of right now, we figure that we will have to change each host manually to recieve an IP address. I have seen scripts on the internet that will automate the process, but have to be ran as an administrator. Anyone have a suggestion for this?

    Also, what else should we take in to consideration regarding the project?

    We want to make sure that we plan this project out correctly and try to avoid and extra work for us. Any suggestions will be greatly appreciated.
    MCITP:SA, MCSA 2003, MCP, CCNA, A+, Net+, Security+

  • #2
    Re: Static to DHCP Adressing Planning

    Originally posted by boondock View Post
    Is there anyway to turn on DHCP on each VLAN while we still have static hosts, but yet prevent ip address conflicts?
    Create reservations in the DHCP server that reserve an IP address for each MAC address, making the IP address for any given MAC address the same as it is currently (fixed). When you change the host from fixed to dynamic, it will receive the same IP again. By doing this, you are "pre-populating" your hosts with (the same) IP aaddresses in readiness for going over to DHCP. Therefore, there will be no overlaps, and no dynamic IPs will take up the value of a static one, hence no duplicates.

    To discover any given IP address's MAC address, ping the IP address first then run arp -a but be sure to run arp immediately after pinging the IP address as we want the arp table to be up to date. I know you are on fixed IP so that shouldn't make a difference, but I think it is good practice to make sure arp table is up to date.

    Originally posted by boondock View Post
    As of right now, we figure that we will have to change each host manually to recieve an IP address. I have seen scripts on the internet that will automate the process, but have to be ran as an administrator. Anyone have a suggestion for this?
    To change the NIC from fixed to dynamic you must be an administrator, so run the script (which can be a netsh command) as Administrator by having the script as a logon script for your Administrator account, then the script will run as soon as you logon to the workstations, and you only have to wait a few seconds, then you can immediately logoff. Saves a bit of time. Make sure the script does not run when the Administrator logs onto the server, and when you have done all workstations, get rid of the script.

    Actually, there may be a better way but I am not so sure about this idea: perhaps a computer startup script in GPO has the power to change an adaptor from fixed to dynamic, but I am not sure, maybe someone who knows can tell us or you can try it out yourself to see if this is a valid suggestion. If it is, you do not need to walk to every workstation.

    OK, I just had one last thought while typing this - there are ways to do "runas" available, so if you want a login script that runs under the user account, but runs with Administrator rights, use one of the RUNAS tools available. See SANUR for a good solution to this.
    Best wishes,
    PaulH.
    MCP:Server 2003; MCITP:Server 2008; MCTS: SBS2008

    Comment


    • #3
      Re: Static to DHCP Adressing Planning

      Originally posted by boondock View Post
      Is there anyway to turn on DHCP on each VLAN while we still have static hosts, but yet prevent ip address conflicts?
      In Windows there is what is called Conflict Detection. I believe it breaks down to the DHCP server trying to ping the address before it assigns it to insure it is infact free. It might be worth looking to see if your DHCP server has something similar.
      If it hasn't you could possible use a Windows server as your DHCP server at first and then migrate off it. This would be something like giving short leases to your clients in one VLAN/subnet until you are confident all static addresses have been removed from that particular VLAN/subnet. Then activate your planned DHCP server for that scope and finally de-actiavte that scope on the windows DHCP server.
      I don't know anything about (you or your) computers.
      Research/test for yourself when listening to free advice.

      Comment

      Working...
      X