Using a secondary ip helper address on the same Vlan

[yuricyrino]

Hello All,

I would like to purpose the following scenario, a small network that has two DHCP servers running on different subnets having DHCP scopes for the same VLAN, just different range.

At Users Vlan 30, I have both serves configured as helper-address.

The question now is that, does it the DHCP requests are going to be sent to both servers at the same time or they are going to be sent randomly?

I made some tests and notice that the PC0 firstly obtained the IP from Server0 and PC1 from Server1.

On second attempt both PCs acquired the IPs from Server0 only and many other test performed I saw the opposite and so on.

Could you help me to clarify my understanding on this scenario?

[Mark Malone · Accepted solution]

The question now is that, does it the DHCP requests are going to be sent to both servers at the same time or they are going to be sent randomly?

Requests get sent to both servers from the end device and the first server to respond usually gets used by end device

[yuricyrino]

So in the case of one DHCP server failure, if the user packet arrive into this server, the end user will not obtain the IP?

Or the the working server is going to reply this packet?

[InayathUlla Sharieff]

Hi,

when there are two DHCP servers on the network, and IP helper addresses are configured for each server. However, only one server receives most of the DHCP address requests.

In order to verify that only one server receives most of the requests, it is necessary to perform a sniffer trace on the ports connected to DHCP servers.

2nd Questoin:-

So in the case of one DHCP server failure, if the user packet arrive into this server, the end user will not obtain the IP?

Or the the working server is going to reply this packet?

Switch will get to know that the attach interface is down so when dhcp request udp packet comes on to the switch it will re-direct to the other server automtically.

Regards

Inayath