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Need to keep DHCP Pool from running out of IP addresses

Posted on 2011-09-22
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Last Modified: 2012-06-21
Hi,
I keep receiving the following alert from Microsoft MOM 2005 for various DHCP scopes in my environment and was wondering if there was some free tool or a way to automate the removal of old leases in order to keep freeing up addresses in the DHCP pool automatically. I already tried cutting down the lease time but still running into the same problem. In the event you cannot extend the IP subnet mask there has to be some automated way to keep the DHCP pool from running out of addresses. Thanks for the help.

-----Original Message-----
From: MOM1@domain.com [mailto:MOM1@domain.com]
Sent: Tuesday, September 20, 2011 9:50 AM
Subject: Operations Manager Critical Error Alert on Domain\Server

Severity:  Critical Error
Status:  New
Source:  DHCP Server 2003 - Scope Monitoring: Scope: [10.x.x.x] WLAN Guest Scope
Name:  The DHCP Scope is running low or out of available Addresses
Description:  The DHCP Scope named "[10.x.x.x] WLAN Guest Scope" has the following address status:

Free Addresses:         0
Addresses In Use:       125
Percent Addresses Free: 0%
Member of Superscope:   False
Domain:  
Agent:  
Time:  9/20/2011 09:50:01
0
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Question by:leporej092170
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7 Comments
 
LVL 10

Accepted Solution

by:
SuperTaco earned 100 total points
ID: 36584324
Do  you have a lot of machines that coem n and out every day?  Try reducing your lease time
0
 
LVL 7

Assisted Solution

by:tharstern
tharstern earned 100 total points
ID: 36584630
You could use a logoff script containing  

ipconfig /release

for those clients that need it.

0
 
LVL 23

Assisted Solution

by:yo_bee
yo_bee earned 100 total points
ID: 36584649
What is your total count of devices that require IP's?
You seem to be using a Class A address scheme, but can't confirm this without a subnet.

Even if you have a class c  subnet you should have 254 addresses available.
What is your exclusion range?
What is your available range?


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LVL 4

Assisted Solution

by:ZephyrTC
ZephyrTC earned 200 total points
ID: 36584694
Also, what is your lease time?  It shows that 125 addresses have been used and 0 are available.  Yo Bee is on to something.  It should be as simple as modifying the configuration of the DHCP pool a little bit.

Example:
10.x.x.0-254 would the the entire scope for the class C range with a subnet of 255.255.255.0.  you would want to then configure the exclusion range to cover the static devices in your network.  IE, if your default gateway is 10.x.x.1 and you have a couple printers in the 10.x.x.20, and you have a server or two starting at 10.x.x.10, you would want to set the exclusion range to be 10.x.x.1-10.x.x.50.  This prevents the DHCP server from assigning an ip address to your WLAN guest that is already assigned statically to your network and management devices.  If you need instructions on how to go about setting this, please don't hesitate to ask!
0
 
LVL 4

Assisted Solution

by:ZephyrTC
ZephyrTC earned 200 total points
ID: 36584701
Update:

If your corporate network is sharing the same class C subnet with your WLAN guest network (IE, you have used VLSM to carve out a section of the subnet for your WLAN guests), you may need to restructure the guest IP Range to something like this:

Corporate network:
IP: 10.0.0.1-254
Subnet: 255.255.255.0

Guest Network
IP: 10.0.1.254
Subnet: 255.255.255.0
0
 
LVL 23

Expert Comment

by:yo_bee
ID: 36584706
How are you running out of addresses on the Guest, unless it's an open network with no password protection and you have rouge people connecting from outside your firm.

0
 
LVL 23

Expert Comment

by:yo_bee
ID: 36584722
Also can you check your List of Lease Addresses and see if there are any unknown machines or other devices listed .
If this is true then my last comment might be heading in the right direction.
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