Which DHCP server to use?

[Kenneth McCoig]

I currently have CME on 3945 ISR with DHCP server enabled. To prevent my phones from pulling DHCP ipv4 addresses from my Windows domain controllers we configured all my switches for voice VLAN 101 and configured the following in the CME:

interface GigabitEthernet0/1
no ip address
duplex auto
speed auto
!
interface GigabitEthernet0/1.101
encapsulation dot1Q 101
ip address 10.0.100.1 255.255.255.0

ip dhcp pool VOIP
network 10.0.100.0 255.255.255.0
default-router 10.0.100.16
option 150 ip 10.0.100.1

ip dhcp excluded-address 10.0.100.1 10.0.100.20

This weekend I am cutting over to my new CallManager on BE6K with 2921 CUBE. CUBE is strictly a gateway to my service provider, no SRST, no analog ports. I would like to keep the voice traffic on VLAN 101. My question is, who should be the DHCP server? Should it go on the CM, my Windows DC, or the CUBE? I read in Cisco docs that Cisco doesn't recommend anyone use the DHCP server in CM. If on the CUBE I know I can easily copy over the DHCP config from the CME. If on the Windows DC I don't know how to configure the VLAN or the TFTP. 

Am I overthinking this??

Thanks,

-Kenny

[Chris Deren · Accepted solution]

2 most common scnarios are to use centrelized DHCP server such as MSFT DHCP for ease of administration, or keep it local on local switch/router.

Dont use CUCM for it, nor voice gateway.  

[Kenneth McCoig]

Thank you Chris. I prefer to keep it segregated from my Windows network unless this will somehow cause problems with Jabber clients on the workstations later on.
So the only other option then is my core Cisco switch. Just a copy/paste of the CME DHCP config above and I should be good?

[Chris Deren]

DHCP location has no bearing on Jabber functionallity.

Core switch is also OK destination, however if I was to use centrelized DHCP I would definitely put it on MSFT DHCP server if one is available.  Basically I would use the same DHCP server that is providing DHCP services to the data VLANs.

[Kenneth McCoig]

I can understand ease of management. Right now my Windows/data network is 10.0.0.0/21 VLAN 1 and my phones are 10.0.100.0/24 VLAN 101.

So if I understand this correctly, on my Windows DHCP I add scope 150 which points to my new CM (which has TFTP service running). Then as long as all my switches have 'switchport voice vlan 101' I should be OK? I just need to configure VLAN on CM.

Does that sound right?

[Chris Deren]

Correct, dont forget to add helper address on the vlan interface to point to the DHCP server.

The option 150 can be either added individially to each scope or you can make it global on the windows DHCP server.

[Kenneth McCoig]

Where would the helper address go? I won't need it on the CUBE so I assume you mean all my switches? On all my switches right now I only have

interface Vlan1
 ip address 10.0.0.xxx 255.255.255.0

Where xxx is the ip of the switch.

Is there some other place I am missing?

[Chris Deren]

IP helper goes on layer 3 interface for the network only if the DHCP is on another network.  interface vlan1 would be it for one of the networks.

[Kenneth McCoig]

OK I will give it a go. Thank you for all your help!!

[Chris Deren]

My pleasure and good luck.

[juniorkakou]

HI Ch

here's the vlan configuration on a CBS250, except that the pc's connected to the vlan don't receive dhcp server addresses from windows server