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Beginner

DHCP Server moving to new server on new host

Hi All,

apologies I know there are 20 million articles on DHCP relaying but I need to get this sorted.

 

We currently have a Windows 2012R2 DHCP server running and working just fine. I am retiring the 2012 server and replacing it with a 2019 based DHCP server (VM) based on a different host.

 

My current setup has the following;

 

ip helper-address 192.168.200.0 192.168.10.10 37 42 49 53 137 138

and 

 

ip dhcp relay address 192.168.10.10

for reasons that I don't fully understand....

 

So by way of a test..I've setup the new DHCP server with a simple scope of 192.168.254.20 - 192.168.254.30.

I've then added 

 

ip dhcp relay address 192.168.10.12
ip helper-address 192.168.254.0 192.168.10.12

to my config.

I've also configured a port on the 254 vlan (which has an ip address of 192.168.254.11)

if I connect a PC to that port however I'm unable to get an IP address.

 

If I set the IP address manually I can ping the gateway and the new DHCP server (192.168.10.12) so i'm just wondering if there's anything I'm missing.... or should that work from a cisco config point of view?

 

Kind regards.

 

Paul.

5 REPLIES 5
VIP Mentor

Re: DHCP Server moving to new server on new host

Hi
ip helper address should be the DHCP server IP address and applied on the L3 boundary like the SVI the user is on , all it does it changes the broadcast packet to unicast , it used when the server and client pass a L3 boundary so the DHCP packet can reach the user across the subnet
VIP Expert

Re: DHCP Server moving to new server on new host

Hi,

All you need is the

ip helper-address <ip of the DHCP server>

On the router interface or the SVI.

There is no need for the relay command.

HTH

VIP Collaborator

Re: DHCP Server moving to new server on new host

Hello,

What model of L3 are you using? Because in most of cisco's device is necessary only "ip helper address <ip of dhcp server>" as far i know Cisco SG Familiy this is not configured using ip helper address, it is using ip dhcp relay.

Regards

Jaderson Pessoa
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Beginner

Re: DHCP Server moving to new server on new host

Hi Jaderson,
yes I would agree with you... I have the IP DHCP relay address commands in there... for that reason. That said If I take out the existing ip-helper commands it seems to break DHCP....
VIP Collaborator

Re: DHCP Server moving to new server on new host

Because of it i have asked what L3 device you are using, but even that you have the both family there isn't necessities to apply both commands under the same device.

I suggest to you: If your Cisco switch is not SG-FAMILLY, use only "ip helper address <ip of dhcp server>". If is SG-FAMILLY, use "ip dhcp relay" under svi and enable it globally.

If helped you, please mark as solved and rate all post that helped you, it will help other people with the same doubt.

Best regards,

Jaderson Pessoa
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