Utilizing Windows DHCP Server

[Zydain]

I've been working on configuring my first Cisco Router (ISR 4321) and I was hoping someone could point me in the right direction.  Working through this, I was setting up DHCP on the router, and was confused on how to this might affect my current environment that uses DHCP from a Windows Server.

If I'm using a Windows Server for DHCP, do I need to configure the router to utilize that server, or will the Windows Server just automatically be the primary DHCP provider for the LAN it's in?

[pman · Accepted solution]

If you have decided that DHCP SERVER will be a windows server Then:

1. on router - 

make sure that there is network connectivity between the windows server and the router (usually the default gateway of the users. e1/interface vlan 20 in the examples below)
2. on router - 

Set ip helper-address <DHCP SERVER IP> in interface which will be used as the default gateway of the USERS

3. on DHCP Server - 

under the DHCP scope set option=3 with ip address of the router (e1,interface vlan 20 in example below)

Example router configuration:

Example 2  router configuration:

Example DHCP server option 3:

  

 

[Georg Pauwen]

Hello,

with 'I was setting up DHCP on the router' I assume you mean you have configured something like the below on your router:

ip dhcp excluded-address 192.168.1.1

!

ip dhcp pool LAN

network 192.168.1.0 255.255.255.0

default-router 192.168.1.1

dns-server 8.8.8.8

if you have configured this AND a Windows DHCP server in the same 192.168.1.0/24 network, it comes down to which of the two, the router or the Windows DHCP server, is the first to respond to the DHCP broadcasts sent by the clients. Most likely, the router will win, but the results are usually arbitrary, so it is recommended to use either one (router OR Windows server), but not both at the same time.

[paul driver]

Adding an additional dhcp server into a network needs to be controlled especially if the new dhcp service is on a router and not a dedicated server as you won’t be able to migrate the dhcp database from server to server

Also you should not leave it to whatever server responds first to the dhcp requests, you should be deterministic in what should happen, as such if the new server is to accommodate the same subnet as the current dhcp server then you need to make sure of duplicate allocation which could be accomplished by decreasing the lease times from the current dhcp scope/server and then disabling the server service, then bring up the new server after the revised lease time has expired.