PXE boot hangs at a MTFTP prompt for 10 -15 minutes (4272601)

PXE boot hangs at a MTFTP prompt for 10 -15 minutes

When trying to PXE boot a machine to a SDA or to an RSA, PXE hangs at an MTFTP prompt for 10 to 15 minutes. Sometimes it will complete the PXE boot after this waiting period and sometimes it will time out. Some PXE clients may seem unaffected while others do not, however all clients sharing the same DHCP servers (and the same DHCP ip pool will all exhibit the same behavior )  

 This behavior is usually caused by DHCP server with option 43 (vendor specific information) set. This option is an ascii value which represents an IP address. It is used to allow lightweight Cisco Aironet access points (LAPs) to join specific Wireless LAN Controllers (WLCs) when the WLC is in a different subnet than the LAP. Unfortunately the PXE bootrom will grab the Option 43 ip address and use it instead of the option 66 that is expected. If the network architecture contains more than one DHCP server and some them are not serving out option 43, the effect on the PXE client would be some of them (using the affected server) would exhibit this hang/timeout issue and others ( using DHCP server without this option ) would not.

The best solution is to remove any option 43 settings on the DHCP server. Second best would be to ensure the option 43 is outside the IP pool used by the PXE clients.