DHCP on a Windows Server

dustinalbright2 · 2019-03-21T21:15:52.000Z

So I am working with DHCP on a new Windows Server 2016 in a Cisco environment trying to recreate a server that has just passed away unexpectedly. I have created 5 different DHCP scopes, two of which I will need at a later date when they implement a new wifi infrastructure.

The general idea is: 172.16.240.1/24 is one scope, and 172.16.242.0/24 is another that will be used for client PC’s or mobile devices. I looked in the the switch and VLAN1 has the ip address 172.16.240/0 so it makes sense they get pushed to that DHCP scope

My question is, how do I overflow them to the second scope? I very quickly ran out of addresses because 1-50 will be reserved for static IP’s.

I pulled this from the switch:

interface Vlan1
ip address 172.16.240.2 255.255.255.0
no ip redirects
!
interface Vlan2
ip address 172.16.2.2 255.255.255.0
!
interface Vlan3
ip address 172.16.242.2 255.255.255.0
!
interface Vlan4
ip address 172.16.239.2 255.255.255.0
!
interface Vlan6
no ip address

dustinalbright2 · 2019-03-21T22:36:12.000Z

I think I figured out that I need ip helper 172.16.240.11 on the 242/vlan3. I rebooted a computer and it got a 242 address.

kevinhsieh · 2019-03-22T00:58:57.000Z

You don’t “overflow” from one scope to another. You need to puts clients on a different VLAN (which would use a different scope), or change the size of the scope…and possibly the subnet mask.

It looks like you’re routing on the switch, in which case use ip helper to tell each VLAN where to find the DHCP server(s).

PatrickFarrell · 2019-03-22T02:59:03.000Z

Each VLAN on your layer 3 switch other than the VLAN the DHCP server resides in will need a DHCP helper pointing to your DHCP server. There is no “overflow”. A computer on VLAN 2 will get an IP address in the 172.16.2.x scope. If it somehow managed to get a 172.16.3.x IP on VLAN 2, it would not be able to communicate on the network.