DHCP scope full, event ID 1020

Question

Hi, one of our Windows 2008 R2 Domain controllers is returning the following warning message on almost a daily basis:
Log Name:      System
Source:        Microsoft-Windows-DHCP-Server
Date:          19/11/2014 11:32:41 AM
Event ID:      1020
Task Category: None
Level:         Warning
Keywords:      Classic
User:          N/A
Computer:      computername.domain.x.x
Description:
Scope, 10.x.x.0, is 83 percent full with only 39 IP addresses remaining.
Event Xml:
<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
  <System>
    <Provider Name="Microsoft-Windows-DHCP-Server" Guid="{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}" EventSourceName="DhcpServer" />
    <EventID Qualifiers="0">1020</EventID>
    <Version>0</Version>
    <Level>3</Level>
    <Task>0</Task>
    <Opcode>0</Opcode>
    <Keywords>0x80000000000000</Keywords>
    <TimeCreated SystemTime="2014-11-19T00:32:41.000000000Z" />
    <EventRecordID>12980</EventRecordID>
    <Correlation />
    <Execution ProcessID="0" ThreadID="0" />
    <Channel>System</Channel>
    <Computer>computer.domain.x.x</Computer>
    <Security />
  </System>
  <EventData>
    <Data>10.x.x.x</Data>
    <Data>83</Data>
    <Data>39</Data>
  </EventData>
</Event>
Upon review of Microsoft Support online, I found the following article which illustrates a few options:
http://support.microsoft.com/kb/255999/en-au
What would be the logical choice for us, having the 10.x.x network?
Ideally, it would be good not having to re-subnet anything if possible, or re-create the scope.
Would a scope extension require a reboot of the server? Never done this before, so thought I should ask.

Answer 1

Hi,
According to your description, my understanding is that DC prompts an warning event ID 1020, indicate 83% full with DHCP scope.
By default, the threshold value for firing of event 1020 is 80%. Estimate devices number, contrast with the number of IP address in this scope, if the percentage is less than 80%, you may try to reduce the lease duration and decrease the cleanup interval.
This can help to speed the reclaiming of expired scope IP addresses.
To reduce the lease duration:
1.At the DHCP server, click Start, point to Administrative Tools, and then click
DHCP.
2.In the DCHP console tree, right-click the scope you want to configure, and then click
Properties.
3.On the General tab, under Lease duration for DHCP clients, type the new lease duration.
To use a Netsh command to set the cleanup interval time:
1.At the DHCP server, click Start, click Run, type
cmd, and then press ENTER.
2.Type netsh dhcp set databasecleanupinterval <NewInterval> (where "NewInterval" is the amount of time in minutes between DHCP database cleanups).
As an existing DHCP scope, its subnet mask can’t be changed. If the Start Address and
End Address do not currently include all addresses for your specific subnet, you can increase the number of addresses in the scope by extending the
Start Address or End Address in the scope properties. This operation needn’t reboot.
If neither of above 2 suggestions is applicable, new a DHCP scope or reference
KB255999 (resubnetting and superscoping). At the same time, you need to change your network topology.
Best Regards,           
Eve Wang