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DHCP IP address

Thomas N
Thomas N asked
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I had a DHCP reservervation for a machine I had deleted by accident and another machine took the IP. Is there a way to get that IP back and reserved? 2008 server
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Sr. Systems Administrator
Commented:
release it (ipconfig /release from elevated command prompt) then reserve your address then ipconfig /renew on the other system to get a new address
Thomas GrassiSystems Administrator

Commented:
Add to Seth's answers

after you make your reservation turn on the computer it is for and make sure it obtains the correct address before you do the ipconfig /renew on the other computer

then you should be ok
Will SzymkowskiSenior Solution Architect
Most Valuable Expert 2015
Top Expert 2015

Commented:
You can also exclude this IP completely from your scope. This way if you were to remove a reservation in the future and want to assign it to another machine (say you got a new Laptop) you do not have to risk the chance of it getting it picked up by a DHCP client.

Best practice is to exclude a range of IP's so that you can use them for Reservations if needed.

Will.
Will's suggestion is valid, but personally I like using reservations rather than excluded IP addresses, because reservations show up in the DHCP list of addresses whereas excluded IPs don't.

My tip - if you have an IP reserved and the machine/device is going away but you want to make sure that the IP address is available for another reservation in the future, then instead of removing the reservation, simply change the MAC address on the reservation to something invalid.  You can even just use all 0's for the MAC address. This way the reservation stays in place but cannot be used by anything until you set a valid MAC address for it.
Will SzymkowskiSenior Solution Architect
Most Valuable Expert 2015
Top Expert 2015

Commented:
Will's suggestion is valid, but personally I like using reservations rather than excluded IP addresses, because reservations show up in the DHCP list of addresses whereas excluded IPs don't.

I think you missunderstood me. I meant create a block of IP addresses to exclude and STILL create reservations with the IP's that have been excluded. This way you can track in DHCP who has what IP address associated to the MAC address of the NIC and to also avoid the issue the user experienced in this Question.

There is going to be some point where you need to change a reservation, and when you remove that Reservation if it is part of the Scope, then there is potential for it to get picked up by a DHCP client (as i have stated already, and we have seen this behavior based on the users question).  

Create your Exclusions and use the IP's that have been excluded for your Reservations.

Will.
Re-create your reservation with the target's mac address.  On the system you don't want to have that IP after the reservation made open command prompt as admin and type in IPCONFIG /RENEW * it should release and renew the IP and it shouldn't get the reserved IP .