PXE booting with WDS using IP Helpers in different Subnet

Problems:

PXE boot across different VLANS not working.

Quoted from Kervin   PXE Boot Basics.

Booting from the network using the PXE protocol involves a simple series of DHCP packets. There are three parties involved: the DHCP server, the PXE server, and the client.

1. The client broadcasts a DHCP packet asking for the address of DHCP servers (servers that can hand out IP addresses). In the same packet, the client also specifies that it is looking for PXE (network boot) servers. This is known as a ‘discover’ – the client wants to discover where the servers are.
2. The DHCP server responds with a broadcast packet (which simply tells the client that it is an address server). This is known as an ‘offer’ – the server is offering its services.
3. The PXE server responds (which tells the client that it is a boot server). This is also known as an ‘offer.’
4. The client sends the DHCP server a message asking for an IP address.
5. The DHCP server sends the client an IP address that is now assigned to it.
6. The clients sends the PXE server a request asking for the path to the Network Boot Program (NBP).
7. The PXE server responds with the NBP path.
8. The client downloads the NBP and runs it.

Solutions:

configure the routers/switches to forward the client request to the PXE server and DHCP server

For example: add those lines in the switch.

ip helper-address 192.168.33.20     (this is the WDS server address)

ip helper-address 192.168.33.10      (this is the DHCP server address)

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