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New Member

DHCP over VLANs

I am running a DHCP server on VLAN1 and I am planning on putting workstations on VLAN20. Can anyone help me with the configutation? My backbone is collapsed into a 6509 and I also have a 7206 router running on the network as well.

7 REPLIES
Purple

Re: DHCP over VLANs

On vlan 20 all you should have to do is add ip helper addresses for the dhcp servers .

int vlan20

ip helper -address xxx.xxx.xxx.xxx

New Member

Re: DHCP over VLANs

Glen - Thanks for the info. However, I already have that command on the interface and workstation still cannot reach the DHCP server. It cannot even ping it.

Purple

Re: DHCP over VLANs

If your workstations are on a Catalyst switch make sure you have portfast turned for the workstation ports otherwise the workstations will time out before the Catalyst puts spanning tree into the forwarding state .

New Member

Re: DHCP over VLANs

you will have to ensure that there is proper routing between vlan1 and vlan20, for the ip-helper address command to work.

Best Regards / Sampath.

Sampathsr@yahoo.com, New York, NY.

New Member

Re: DHCP over VLANs

I suggest you to check the VTP information of the Trunk, Vlan 20 maybe in the inactive status.

Before introduce the DHCP, you'd better assign the static IP address to the workstation and check the ping.

New Member

Re: DHCP over VLANs

Quick idea, check if there are any access lists that prevent routing from one vlan to the other.

New Member

Re: DHCP over VLANs

After making sure that the VLAN20 is able to route between segemnts on the router and the DHCP server is not on the VLAN20 segment.

To help with the DHCP request and hand shake process. You will need to put in the IP Helper statement on the VLAN20 segement of the router to help in the DHCP process.

For example Routerip helper *.*.*.*(Address of you DHCP server)

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