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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

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    If this is all on one VLAN, it's not going to work. The dhcp server will default to the first defined scope. – 84104 May 5 '16 at 16:39
  • Ok. That why I am getting IP from first scope only. which is my 192.168.1.0/24. And 2.0/24 never release the IP to any system. So is their any other option I have left. – user205223 May 5 '16 at 16:42
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    Change your subnet mask to /23 and forget about using multiple DHCP scopes. – joeqwerty May 5 '16 at 16:44
  • That will increase broadcast in my LAN. And also right now my 1.0/24 network is on static network only. Shall I need to change each of them to /23. Kindly correct me if I am wrong!! – user205223 May 5 '16 at 16:46
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    If your equipment is on the same physcial VLAN, then a broadcast is a broadcast. The /23 vs two /24 doesn't change anything, since the broadcast is an Ethernet (layer2) broadcast. – Zoredache May 5 '16 at 16:49
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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.

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  • Yes. Its a windows 2012 r2. Trying to figure out things with this super scope feature of windows – user205223 May 5 '16 at 16:51
  • So I quickly figured out that superscope feature in DHCP. Here I have only one gateway for 1.0/24 which is 192.168.1.10 which I configured in 1st scope. But after adding the same for second scope doesn't seems to be workable for me. I believe there should be another gateway like 192.168.2.10 for 2.0/23 subnet which is never exist. Same goes for my DNS servers as well. – user205223 May 5 '16 at 17:19
  • Each subnet must have a gateway with an IP address within the subnet. Without it there is no (easy) way to talk to other subnets. You must connect your access router to the new subnet, alternatively use an addtional router. – Zac67 Aug 26 '17 at 18:21
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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.

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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.

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