We have two LAN in my enterprise.One LAN is for server and other is for users.Cisco Router act as a DHCP server for the user LAN.Now we are planning for PXE boot for user LAN.My PXE boot server is located in the server LAN.What are the changes needs to be done at the router to make this work.
on client vlan facing router interface you need the command
ip helper-address pxe-server-address
this command converts unroutable packets with broadcast destination to routable packets with unicast destination = pxe-server-address
one field in the packet is updated with the router's IP address of client facing interface so that DHCP server can pick up an IP address from correct address pool
to be noted LAN switch ports should be configured with spanning-tree portfast otherwise PXE boot can fail for the STP standard timers (up to 30 seconds before making the port operational)
Hope to help