Question : CISCO VLANS Acting as DHCP Relay Agents

Hi,

I have setup 2 VLAN's on a Cisco 4507R Switch.  I want my workstations on VLAN 2 to get a DHCP allocatied IP Address from the DHCP Server on VLAN 1.

VLAN 1 Servers (includes my DHCP and DNS Server)
VLAN 2 Workstations (new workstation subnet)

The DHCP Server on VLAN 1 has 2 scopes defined and activated

Scope 1 - is for the existing workstations which are also located on VLAN 1 IP Address range 171.197.155.50 - 100
Scope 2 - is for the new subnet we are migrating the workstations to Address range 171.197.154.101 - 200

VLAN 2 has an ip address of 171.197.154.4 and has an IP Helper address setup pointing to the DHCP Server on VLAN 1 171.197.155.4

When I assign a workstation on vlan 2 with a static ip address which happens to fall within the DHCP range configued (there are no other workstations connected to the switch in vlan 2) it can ping the dhcp server on VLAN 1 and vice versa.

When I  set ip to use DHCP to get an ip address I get

The following error occurred when renewing the adaptor. The DHCP Client obtained an IP Address that is already in use on the network.

Any ideas?

Thanks

Pops




 

Answer : CISCO VLANS Acting as DHCP Relay Agents

Your subnet masks might be wrong.

We are assuming the subnet mask for both networks is /24 (255.255.255.0). If not, please send this info and we can help.

The other most common way that the workstation on vlan 2 gets a lease from vlan 1 is that there is a connection between a vlan2 port and a vlan1 port amongst your switches so the workstation on vlan 2's broadcast is getting to the dhcp server without the relay agent (ip helper) setting the GIADDR field (gateway internet address) to tell the DHCP sever that the request came from a different subnet.

Just thoughts.