3560 - DHCP Helper address config - is this possible?

Answered Question
Feb 19th, 2008

Hi,

I think I know the answer to this myself, but I need to have it confirmed,

I have a 3560 with a single vlan configured and it utilises IP Helper-Address command for DHCP to the entire Vlan.

A Customer has asked for DHCP to be "Disabled" on certain ports on the switch. Can you let me know if there is a command for this or if DHCP is either enabled/disabled with the Helper-Address for the entire switch per vlan.

thanks,

brian

I have this problem too.
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Correct Answer by lamav about 8 years 9 months ago

Glad to be of help

please feel free to rate my post if it was helpful

Thanks

Victor

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lamav Tue, 02/19/2008 - 10:18

brian:

When you configure the ip helper-address command under the L3 vlan interface, it applies to all DHCP-enabled clients that are plugged into a switch port on that vlan.

Im not sure why you would want to exclude some hosts from the DHCP process, but you can always hardcode them and exclude the address range from the DHCP scope on the DHCP server.

Am I making sense or am I misunderstanding what you are trying to achieve?

Victor

joeheaton Tue, 02/19/2008 - 10:26

Or you could reserve specific IP addresses within DHCP for those clients, based on their MAC addresses.

JORGE RODRIGUEZ Tue, 02/19/2008 - 10:26

In addition to Victor's remarks, I am not ware you can disable dhcp on a l2 switchport basis, ip helper address is either enabled or disabled on a per SVI interface or physical port on a router basis. Unless there is a new feature out there you can disabled dhcp per port then I would like to learn it.

what you could do is to create another subnet and vlan and have that vlan not used herper address, however, what Victor indicated in dhcp exclution on DHCP server seems to be the most common scenario used.

Rgds

Jorge

bmeegan Tue, 02/19/2008 - 10:36

Thanks Guys,

I'm understanding and agreeing to all you have posted on this.

Option is to create a separate vlan and put static hosts into it, with no IP helper address command.I believe the problem lies with the DHCP server itself (DHCP not configured on the switch) and the users been given wrong information about the scope details.Original problem was that IP's outside of the "allocated scope" were being assigned to clients on the Vlan.

Brian

Correct Answer
lamav Tue, 02/19/2008 - 11:58

Glad to be of help

please feel free to rate my post if it was helpful

Thanks

Victor

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