How to add two VLANs for DHCP Pool

Question

Currently one of my customer has DHCP pool created in Cisco Switch and ip address range is 192.168.25.0/24 (This is a VLAN). Now they have 230 devices and They are going to increase device count by 100. DCHP assigned for Wireless network and cisco 2500 Wireless controller also available.

I cannot change subnet and increased usable IP addresses count because there are many dependencies.

What is possibility of Adding two VLANs to one DHCP Pool? If it is possible, How do we add? What kind of changes necessary from wireless controller?

Or what is solution for this issue?

Answer 1

Now they have 230 devices and They are going to increase device count by 100.

Within the same subnet? Then you'd have to supernet that subnet to e.g. 192.168.24.0/23.

I cannot change subnet and increased usable IP addresses count because there are many dependencies.

Adding another subnet/VLAN is a better option anyway. As Jesse's already answered, that requires a second DHCP pool as well.

What is possibility of Adding two VLANs to one DHCP Pool?

That isn't possible. You can have multiple pools for a single VLAN but not the other way around.

What kind of changes necessary from wireless controller?

None, if the wireless controller and network stay bridged on the already existing network/subnet and you don't need to the change the default gateway. If you need to change the default gateway to e.g. your L3 switch then that is the change to make there as well (and for the DHCP scopes).

Answer 2

Questions about protocols above layer 4 are off limits here, however, as a very basic explanation on a layer 2 and layer 3 level, you cannot have multiple VLANs using the same DHCP pool (same subnet). Each VLAN would need a separate DHCP pool (separate subnet) to assign addresses from.

For example:

VLAN 100: 192.168.1.0/24
VLAN 200: 192.168.2.0/24

Just to make something else clear, you would also not be able to increase the size of the existing network to share between the 2 VLANs, as that would also cause overlap issues.

For example, if you currently have 192.168.1.0/24 you would not be able to increase the mask to /23 and then hand out the first half for VLAN 100 and the second half for VLAN 200, as this would still create a conflict.

You could increase the mask to /23 (or larger) for the existing network to use for the existing/same VLAN, however, such as if you wanted to have 192.168.1.0/23 associated with VLAN 100. VLAN 200 would still need its own scope, though.

Answer 3

you could add a second range to another vlan. If the switch is a layer 3 switch, it shouldn't be a problem to connect to eachother. If not, a downtime is necessary to adapt the existing one.

Answer 4

There is one option available. Create a new VLAN and create new DHCP scope for this VLAN

Assuming you created new VLAN as VLAN 20

Switch (config)#ip dhcp pool Vlan20

Switch(config)#network 192.168.X.X 0.0.255.255

Switch (config)# default-router ip 192.168.1.1

Switch (config)#dns-server 8.8.8.8

Also create the same VLAN 20 on downstream access switches, and connect newly deployed 100 system to this VLAN 20 and then create an access-list on L3 switch to provide access among VLAN as per business requirements.