DHCP not working across VLANS and subnets on a Cisco 6513

Unanswered Question
Jul 15th, 2008

I have a DHCP server in my first VLAN (101) and it hands out addresses without problem. When I attache a client to another VLAN, no DHCP address. I have an IP helper address in each VLAN as well as the VLAN IP as the gateway on the scope (Windows Server 2008) but nothing.

IOS Native 12.2

Thanks!

I have this problem too.
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lrossignol Tue, 07/15/2008 - 23:15

and I can ping across the VLANS, ping the DHCP server as well. Thanks for any help.

mahmoodmkl Tue, 07/15/2008 - 23:48

Hi

Under u r vlan SVI's issue the command

ip helper-address (address of the dhcp server)

Thanks

Mahmood

lrossignol Wed, 07/16/2008 - 07:02

Yes, I did enter the IP helper-address of the DHCP server under each VLAN interface.

mattcalderon Wed, 07/16/2008 - 09:45

Does the scopes subnet match up with the VLAN interface's subnet?

Also just a quick check that the pc is not set up for static addressing. Don't want to be burned by that one.

Also verify that the port you are plugging into has been assigned to the proper vlan and the command is "switchport access vlan xx"

Other than that, the config is basic. Just use the ip helper to direct the DHCP requests to the server.

lrossignol Wed, 07/16/2008 - 13:14

Does the scopes subnet match up with the VLAN interface's subnet?

Check.

Also just a quick check that the pc is not set up for static addressing. Don't want to be burned by that one.

lol, check

Also verify that the port you are plugging into has been assigned to the proper vlan and the command is "switchport access vlan xx"

check.

Other than that, the config is basic. Just use the ip helper to direct the DHCP requests to the server.

Any other ideas, I've performed all the above commands as well as the helper address.

Have you looked at your server and see if the DHCP requests are reaching it? If you don't see it, we can at least verify that the traffic is actually not getting there. If you see it, then the problem could be something local to the VLAN.

Have you tried sniffing the traffic on the clients as well? Hopefully you'll see the DHCP traffic on the VLAN. Just want to eliminate the possibility that a rogue DHCP server is not sending NAKs to your machine causing the machine discard the DHCP offers.

lrossignol Sat, 07/19/2008 - 11:46

It turns out the DHCP was never authorized, but it would still hand out addresses in the first scope. Authorized the DHCP server with AD on server old network, and it's now handing out ip's across the vlans. Thanks for all the great suggestions!

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