New to iPXE - what could be wrong with DHCP server and/or router?

[NiKiZe]

PortFast is to make sure that STP does not block traffic on the port when iPXE starts, which would cause DHCP to time out

The error you are seing with modprobe vesafb, and BusyBox is likely related to that the linux you where booting did not find one or more files, probably missing initrd. You would need to provide the iPXE script used for us to be able to help. But a guess is that you are passing a http:// or nfs:// link when booting the OS which is not available, so look further up in your output for the actual issue.

This is more related to the (Linux) distribution you are booting, but we might be able to help you anyway.