DHCP between VLANs

[nklv]

VLAN2 and VLAN4 are defined on Cisco 2950. Hosts communicate between VLANs successfully. We use PC-based DHCP server, it belongs to VLAN2. Hosts from VLAN2 can lease IP addresses successfully but hosts from VLAN4 can not. What shall we do in order to use DHCP server in VLAN4 as well?

[amit-singh]

Hi,

Just give the command " ip helper-address

Interface vlan 4

ip helper-address x.x.x.x

or

int fa 0.4

ip helper-address x.x.x.x

HTH

-amit singh

[nklv]

Hi Amit,

I did:

Interface vlan 4

ip helper-address n.n.n.n

I got:

interface Vlan4

no ip address

ip helper-address n.n.n.n

no ip route-cache

shutdown

DHCP does not work for Vlan4 when it is in Shutdown state. As soon as I do:

interface Vlan4

no shutdown

another Vlan99 that we use for network management gets into shutdown state and I can not access the switch by the network. Any idea?

[amit-singh]

You are putting it at a wrong place.

You are putting the command on 2950 switch. Its not the place where you have to give it.

You have to use it on the interface of the Layer 3 device which is doing the routing between the Vlans.

Which device is doing the routing between the Vlans ???

What is the gateway for Vlan4.The interface on the router which the gateway for Vlan 4, you have to put this command in there.

HTH,

-amit singh

[thisisshanky]

Like suggested by Amit, you need a L3 device which is possible a L3 switch or a router. If its a router use this link to configure inter vlan routing between the subnets and configure the helper-address on the sub interface on the router that routes vlan 4.

http://www.cisco.com/en/US/tech/tk389/tk390/technologies_configuration_example09186a00800949fd.shtml