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I just recently added a new subnet for our wireless network to our DHCP configuration for the 192.168.254.0 subnet. Most of the time when wireless clients connect it works just fine. However, sometimes on seemingly random occasions the DHCP server will send out a DHCPOFFER with an IP address on the wrong subnet.

Example:

dhcpd: DHCPDISCOVER from MACADDRESS (ThinkBook2) via 192.168.254.1
dhcpd: DHCPOFFER on 192.168.22.236 to MACADDRESS (ThinkBook2) via 192.168.254.1

Here is the subnet configuration in dhcpd.conf:

subnet 192.168.254.0 netmask 255.255.255.0
{
  option routers 192.168.254.1;
  range 192.168.254.34 192.168.254.254;
  default-lease-time 14400;
  authoritative;
}

How can I make sure the server always sends out an IP address on the right subnet?

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3  
How many network interfaces does the DHCP server have? How are they configured (what IP addresses). Is the DHCP server the router for those two networks? Do you have some other device acting as the DHCP relay for the second subnet? –  Zoredache Jun 29 '12 at 19:05
1  
What DHCP server? What version? –  Chris S Jun 29 '12 at 19:11
    
The DHCP server has one network interface and it has a public IP address. The DHCP server is not the router, everything is connected to a large cisco switch. The cisco switch is configured to manage subnets through vlans. I have read some information about creating virtual interfaces for seperate vlans but I would really like to avoid that if possible. It is ISC dhcp 4.1.1 –  Logan Jun 29 '12 at 19:31
1  
Sorry, figured it out. It turns out my subnet definition was in the context of a shared-network statement in the dhcpd.conf file. Moving it out of there fixed the problem. Thanks! –  Logan Jun 29 '12 at 19:56

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