I've fixed this issue at a number of customers by doing one of two things, 
depending on the installation. You can create a new vlan on the network with a 
new set of IP addresses, then create a new scope on your DHCP server then setup 
ip helpers in your layer 3 switch so DHCP requests get forwarded to your single 
DHCP server.

 interface vlan.0.370
  ip address 10.1.7.1 255.255.255.0 primary
  no shutdown
  exit
 interface vlan.0.380
  ip address 10.1.8.1 255.255.255.0 primary
  ip helper-address 10.1.7.10
  ip helper-address 10.1.7.11
  no shutdown
  exit

Or, the easier method IMHO, especially if you don't have a layer 3 switch, is 
to just change the subnet mask on the network. For example, if you are using 
255.255.255.0, you can change it to 255.255.254.0 to double your ip address 
space or 255.255.252.0 to quadruple your ip address space. Do calculations 
before you do this so you know what new IP addresses are available to you. For 
example, if you're using 192.168.1.0 as your network and you expand the subnet 
mask from 255.255.255.0 to 255.255.254.0, you must use 192.168.0.0, not 
192.168.2.0. In CIDR terms, 192.168.1.0/24 expanded to /23 becomes 
192.168.0.0/23. Does this make sense? I'll be happy to help if you need 
clarification or calculations.

Stephen Loeckle
Lucid Networks

From: Jeremy Bullock <[email protected]<mailto:[email protected]>>
Reply-To: "[email protected]<mailto:[email protected]>" 
<[email protected]<mailto:[email protected]>>
Date: Wednesday, August 21, 2013 9:44 AM
To: Enterasys Customer Mailing List 
<[email protected]<mailto:[email protected]>>
Subject: [enterasys] Secondary Subnet

We are experiencing a 100% DHCP use on one of our subnets/VLANs.  If I add a 
secondary subnet to that VLAN, will the client attempt to get a primary 
address, fail and then use the secondary subnet for an IP?

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