Campus PXE config

Unanswered Question

I'm wondering how you have chosen to get PXE to work in your environment. We are just stating with it and I am getting conflicting info.

The server people say I have to set ip helper-address, but a lot of the documentation I'm finding says just set the option on the DHCP server.

I'm sure both will work (if configured correctly) but what is normal/standard. What did you you?

Thank You

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Giuseppe Larosa Thu, 04/30/2009 - 21:36
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Hello Jeff,

we need to set the additional helper-address for the RIS server(s).

The reason is that the PXE process uses DHCP messages to reach also the PXE server (RIS server).

spanning-tree portfast is also needed on the port.

We do this on demand: the field technician that needs to rebuild a PC on site first tries to perform a PXE boot, if it doesn't work it he/she calls the NOC asking for it.

To be noted that in case of remote branch offices with low speed links can be faster to carry the PC to a bigger better connected office: we have been reported of an 18 hours time to rebuild a PC that was in a branch with only an IPSEC vpn connection to the intranet.

There was a recent thread where possible issues when DHCP snooping is enabled have been analyzed.

There was a bug in first DHCP snooping implementations that caused issues with PXE.

Hope to help


BlueyVIII Fri, 05/01/2009 - 15:02
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We're using Microsoft RIS and had problems when the IP Helper on the VLAN pointed to a host address. We changed the IP Helper so that it pointed to the destination subnet broadcast address and it worked a treat.

From the sniffer traces we did it would appear that for RIS to respond to a PXE request both the DHCP server and the RIS Server have to "hear" the request. The DHCP server repsonds with an address and the RIS server responds with a PXE reply that carries a NULL ip address.

If RIS is running on the same server as DHCP then you'll be OK with the IP helper pointing directly at the host address.


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