Where to put DHCP Server with subnets

Question

I have a general question about where to put the DHCP and how it will work on subnets.

For example if I have a topology as this one with an IP range of 172.33.0.0/22

And I would like to split the network in first two subnets one outside the pfSense (for Network A/B) and one inside (Network C/D/E) to 172.33.0.0/23 and 172.33.2.0/23

And then further divide the inside netowrk (C/D/E) into another subnet with unequal size to 172.33.2.0/24, 172.45.3.0/25 and 172.45.3.128/25 I hope I calculated the subnets correctly.

But now my question where would I put the DHCP to perform the subnetting? And also where would I put it if I'd like to split up the Network A/B in also 2 subnets?

Do I have to configure one DHCP Server on the router to perform the division in two subnets first and then another one on the pfSense for the further division into the unequal subnets?

Answer 1

You should put your DHCP server on whatever network you put your infrastructure services for your clients, such as DNS, Active Directory, etc. Assuming for example, you put it on network A, you configure the pfSense router to enable DHCP relay on Networks C, D, and E.

When clients broadcast a DHCP Discover message, the router will forward those packets as unicast to the DHCP server. In essence the router relays the DHCP data between the clients and the DHCP server.

If you separate A and B, you would configure ip helper-address on the router interface on the B network.

Answer 2

Remember that DHCP does not do subnetting. You design your subnets, configure your routers to allow the different subnets to communicate, and finally add DHCP servers to distribute addresses to devices in those subnets. The DHCP server needs to be configured according to how you've done your subnetting of course.

You can place DHCP servers wherever you like if you design redundancy appropriately : I run just a handful of DHCP servers for a corporate network of almost 2000 locations. The trick is setting up DHCP Relay functionality (aka ip helper in the Cisco world) so that a subnet without a local DHCP server can be served by a server elsewhere.