Boot via iPXE in an environment where there is an existing DHCP server

[lipeng-unisound]

The instruction assumes there is no DHCP servers in the sub-network, so we can start a DHCP service and configure the 'next-server' to our TFTP server to ensure the PXE booting works. However, if there's another DHCP server in the network, it's not guaranteed for the PXE client to communicate to our DHCP service, thus it may failed to know where to load the PXE firmware.

I think I've read some article about how to solve this problem (proxyDNS?), I should add more details in the instruction later.