This document describes the configuration changes required, when the PXE client, DHCP and the OSIM server are on different subnets .
Consider the following example where the DHCP, PXE Machines and the OSIM server are in different subnets/VLANs.
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In this example:
The PXE clients can contact the DHCP server and initiate the DORA process. The Boot Server acts as a DHCP proxy and listens for all DHCP broadcasts.
When the boot server receives a DHCP broadcast from a PXE client, it responds to it and provides the server address that the PXE client needs to use as well as the location of the 'bootfile'. However, the routers connecting these VLAN's do not route the PXE DHCP broadcasts to the Boot Server.
To over-come this, you would need to configure 'IP Helper' (or something similar) on the routers connecting the VLANs to route the PXE DHCP broadcasts to the Boot Servers.
For Cisco routers following is the 'IP Helper' Configuration:
IP helper-address <address of the boot server>
In addition if you are using 'WinPE' boot images you will also need to forward UDP packets over port 4011 using the following command:
IP forward-protocol UDP 4011