DHCP and PXE Helper Addresses

[Mabrito]

Setting up a stand-alone WDS/PXE server.

Current we have helper addresses setup to forward the DHCP requests from the different VLAN's to the DHCP server. The WDS/PXE server we are setting up is on its server. How do we craft the helper addresses so DHCP requests go to the proper server hosting DHCP and PXE requests go the WDS server?

Everything I seen on Microsoft Technet, lists using Helper Address as the recommended way, but assume both services are on the same server.

Our helper address is as follows on each VLAN interface in router:
ip helper-address X.X.X.X

This is a Cisco 3750.

 

[cyr0n_k0r]

You setup the ip helper address to go to the DHCP server.
Then on the DHCP server you set the PXE option in the DHCP scope.

 

[Mabrito]

You setup the ip helper address to go to the DHCP server.
Then on the DHCP server you set the PXE option in the DHCP scope.

Thanks....I was thinking there was a way to say in the helper, PXE requests go here and DHCP requests go here. Guess not. Enabled the DHCP 66 and 67 options and worked like a charm.

 

[timberdoodle]

Thanks....I was thinking there was a way to say in the helper, PXE requests go here and DHCP requests go here. Guess not. Enabled the DHCP 66 and 67 options and worked like a charm.

Microsoft would have you believe it works the way you originally thought, I could never get it to work. Always had to use 66 and 67.

 

[tangoseal]

What is your question? Thanks for the description of what you are doing but do you have a question? I own a 3750E so I might be able to help.

 

[Mabrito]

What is your question? Thanks for the description of what you are doing but do you have a question? I own a 3750E so I might be able to help.

Just setting helper addresses for PXE and DHCP. Since DHCP and PXE are located on two separate servers, having a helper address of "ip helper-address X.X.X.X" will send both PXE and DHCP responses to the X.X.X.X address, which is the DHCP server in my case.

I was thinking there could be a way in the helper address statement to filter out PXE requests and DHCP requests and say, if this is a PXE request, go here and if this is a DHCP request go here.

Is there anyway to get more detailed in the helper address to detect what kind of request (broadcast) it is?

 

[green91]

I know that you guys have already kinda said this, but i wanted to clarify:

PXE is a dhcp option, specifies pxe server and boot image among other things;

ip-helper is used to "route" dhcp broadcasts to a dhcp server not within the same broadcast domain.

If the DHCP server is on the same broadcast domain as the client, there is no need for ip-helper. When a client is looking to PXE boot, it send a dhcp broadcast request for the options related to PXE boot, usually 60, 67, 68 iirc.. (been a while) at the same time it is also requesting an IP.