The purpose of using the following DHCP options is to have a single PXE Representative for multiple subnets.
ip dhcp pool 101
network 172.20.1.0 255.255.255.0
dns-server 172.16.0.1 172.16.0.2
netbios-name-server 172.16.0.1 172.16.0.2
option 13 hex 36
option 66 ip 172.16.16.4
But this has the effect of bypassing the F8 menu. It also has the effect of not allowing the above steps to work for password protecting the PXE menu.
The best way of doing this while still maintaining the F8 menu is to disable all PXE DHCP options and instead configure your vLAN's/subnets to use IP helpers that point to your PXE rep. This way all PXE broadcasts issued by devices will get pointed straight at the PXE rep and will behave as if the PXE rep was local.