IP helper with Windows DHCP (BAD-ADDRESSES)

[andreaswoell]

Hi all,

I have a problem in my network with my dhcp configuration. I am using a Windows DHCP Server for my clients in combination with a Cisco Core Switch (is the Gateway as well). I have two DHCP scopes (10.1.1.0/24 and 10.1.2.0/24) because we ran out of adresses with one scope. On the Core Switch I have configured two ip helper-adresses each from one network and those IP adresses are assigned to my DHCP Server (with two virtual network adapters).

My problem is, that the DHCP got flooded with BAD-ADRESSES and I always have to delete those manually.

Is it necassary to have two ip helper entries on my Core?

Thanks a lot!

[marce1000]

 - Normally you will only need one ip helper entry per VLAN/SVI which does not contain the Windows DHCP server ; also checkout 
 https://learn.microsoft.com/en-us/answers/questions/104532/bad-address-causing-dhcp-to-fill-up

 M.

[balaji.bandi]

Is it necassary to have two ip helper entries on my Core?

Depends on the configuration, if the DHCP split in to 2 Servers you need both the helper address (subject to DHCP Server configured with split of the scopes - not as same ?)

BAD-Address you see due to the IP address already in the network with duplicate.

[andreaswoell]

My DHCP is split into 2 ranges but on the same server. That means I only need one ip helper addr, if I got you right?

Thanks!

[pieterh]

if you currently have configured both subnets active on the same vlan
then your best option is to combine the two scopes to a single scope for 10.1.1.0/23 
gateway address probably remains the same 10.1.1.1 ?
subnet changes from 255.255.255.0 to 255.255.254.0

your DHCP servers can be configured as load-balancing/failover
when doing load balancing, you assign the same subnet (same netmask) , but split the address range in two
so each DHCP server can assign it's own range of addresses

two subnets on the same vlan IS technically possible, but not common practice.

[MHM Cisco World · Accepted solution]

Two IP 

One primary other secondary in same interface and use two dhcp pool and use dhcp relay

Is Work if you use Smart relay.

The primary pool will check if no IP then the dhcp send request to other pool

MHM