Spanning Tree Protocol can cause PXE Boot Failure on Dell Systems
Summary: This article describes work-arounds for Spanning Tree Protocol issues that may arise on newer Dell systems while attempting to image across a network.
Symptoms
This article describes work-arounds for Spanning Tree Protocol issues that may arise on newer Dell systems while attempting to image across a network.
Newer Dell systems may experience difficulties PXE boot imaging across a network when utilizing the Spanning Tree Protocol. The Spanning Tree Protocol is common to Dell, Cisco, other managed switches. Newer Dell System BIOS have a limited time-out when PXE booting to a system during the imaging process. This means the system may not be in a state to receive DHCP information in the time-frame in which the switch is offering the response. If the Spanning Tree Protocol is suspected, the following work-around may resolve the issue:
Delay the PXE DHCP request until the system is prepared to listen:
- Press the Pause button on the keyboard as soon as the DHCP cursor starts spinning on the display
- Wait approximately 30 seconds, then press the Up Arrow to resume the DHCP process
Configure the managed switch to accomodate newer system DHCP requests:
The following link describes another workaround for Cisco Switches utilizing PortFast (See the section titled "Spanning Tree" for a good description of the issue): http://www.dummies.com/programming/networking/cisco/spanning-tree-protocol-stp-and-portfast/ 
The following link describes the steps to enable, or disable the Spanning Tree functionality on a Dell PowerConnect 3248 from the Port Settings page. It also discusses the Fast Link functionality that can be enabled or disabled from the Port Settings page. https://www.dell.com/support/article/us/en/04/sln78969/how-do-i-enable-fastlink-for-a-port-on-a-managed-powerconnect-3248-or-5224-switch-kb-article-130062?lang=en