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I have 192.168.1.0/24 network right now. As number of users growing this is getting difficult to manage them. Hence I added one DHCP server in network with two scopes. One is for 192.168.1.0/24 & another one is for 192.168.2.0/24.

But I am not able get the IP lease from 2.0 scope configured in DHCP server. As I am relatively unfamiliar with DHCP whole this years. Its getting little bit tricky for me right now.

Thanks, Sandesh

user205223
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3 Answers3

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You don't mention what DHCP server you are running, but if Windows and you really want to use 2 subnets, then you need what is called a superscope.

https://technet.microsoft.com/en-us/library/dd759168.aspx

By using a superscope, you can group multiple scopes as a single administrative entity. With this feature, a DHCP server can:

  • Support DHCP clients on a single physical network segment (such as a single Ethernet LAN segment) where multiple logical IP networks are used.

But the above really isn't the best design. You should consider alternatives.

If you are able, you might want to consider adjusting your network mask of your existing subnet instead though, so that your subnet is larger instead of having two subnets. If you don't have lots of statically configured systems this should be pretty easy. Adjust the mask on network interface of all statically configured hosts, adjust the mask in your DHCP scope.

It also might be time to consider implementing VLANs and moving some of your equipment to separate VLANs, and networks. Good options for this is your wireless network devices, IP phones, servers, and so on.

Zoredache
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Easy.

You have the DHCP server on a LAN that contains more than one subnet on top of eachother, no VLANs?

Just add another NIC to the server with its IP in the subnet you want.

The problem is "binding."

If your server is 192.168.5.10/24 but you want it to serve DHCP to 192.168.6.0/24 subnet, windows DHCP server will refuse to serve to the .6 subnet. It doesn't know they are right on top of eachother.

So add another NIC. Assign its IP to be in the .6 subnet and make sure the DHCP service is binding to that interface.

You CAN NOT get away with just assigning a .6 subnet IP to the SAME NIC, I tried. It must be a different NIC (probably because of the MAC address). If your Windows server is a VM you are golden with 0 downtime probably.

Jay303
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As others have mentioned, to have a Windows DHCP server issue DHCP leases from two separate /24 scopes, you would want to implement VLANs. I don't recommend using a superscope unless absolutely necessary. It just gets ugly.

For VLANning, you would need a managed switch that handles VLAN tagging. You would want to tag traffic for a given port as belonging to VLAN 2 or 3 (just example VLAN IDs - you can choose whatever you want aside from VLAN 1, as that is the default VLAN).

To do so, first you would configure VLAN 2 and 3 in the switch with an IP address in either DHCP scope. For example, VLAN 2 has 192.168.1.253, and VLAN 3 has 192.168.2.253.

Then, you want to tag each given switch port as belonging to either VLAN. In most switches, this is done with a command similar to switchport access vlan 2. Substitute 2 for 3 where desired.

After this, configure each VLAN with an IP helper address of the DHCP server. IP helper tells traffic where to go to get a DHCP lease, but tags the traffic for that specified VLAN, and makes the request appear to come from the VLAN IP address. So the server would see the DHCP request coming from either 192.168.1.253, or 192.168.2.253, and issue a DHCP lease in whichever subnet the request came from.

All of this working together would allow you to get a DHCP lease from the desired scope.

Jaypher
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