Interactive Troubleshooter

Published: Sep 29, 2026

PXE Boot Failed: DHCP Option 66 / 67 Fix Guide

Time: 15 mins Level: Beginner

By StepDiag Engineering Team

Reviewed by Ibraheem Taofeeq Opeyemi

Diagnose and resolve PXE network boot failures across Legacy BIOS and UEFI environments. This decision tree covers DHCP Option 66/67 misconfigurations, IP Helper routing across VLANs, TFTP block size negotiation timeouts, and Network Boot Program (NBP) architecture mismatches.

Full Diagnostic Tree & Step-by-Step Overview

At which exact stage of the Preboot Execution Environment (PXE) sequence does the failure occur?

Client hangs at 'DHCP...\n' or fails with 'PXE-E51: No DHCP or proxyDHCP offers were received' or 'PXE-E53: No boot filename received'.
Client obtains an IP address, but fails with 'PXE-E32: TFTP open timeout' or 'TFTP Cannot open file'.
Client downloads the Network Boot Program (NBP) file, but immediately crashes or displays 'NBP file downloaded successfully' followed by a boot loop.
Client downloads NBP and begins loading WinPE/iPXE kernel, but hangs at 0% or aborts with status '0xc000000f' / '0xc0000001'.

What is the network topology and DHCP configuration for the target PXE client subnet?

PXE client and DHCP/TFTP server reside on separate VLANs, but switch lacks IP Helper / UDP Relay configurations.
DHCP Option 66 (Boot Server Host Name) or Option 67 (Bootfile Name) are hardcoded incorrectly on a dual BIOS/UEFI network.
DHCP Server and PXE / WDS Server run on the same physical host, creating a Port 67/68 UDP socket collision.
Standard DHCP server is operating alongside a proxyDHCP (Option 60) server that fails to respond to Option Request Lists.

Missing Switch IP Helper Statements for Cross-VLAN DHCP/PXE Broadcasts

Solution:

Root Cause: Layer 2 Broadcast Boundary Blocking DHCP Discover / PXE Solicit

PXE clients broadcast initial DHCPDISCOVER packets on UDP Port 67 within their local Layer 2 broadcast domain (VLAN). If the DHCP server or PXE Boot Server resides on a different VLAN, network routers/Layer 3 switches drop these broadcast packets by default. Without explicit IP Helper (UDP Relay) addresses configured on the client gateway interface, PXE clients timeout with PXE-E51 or PXE-E53.

# Diagnostic Verification:

1. Capture network traffic on the PXE server interface using Wireshark while booting the client.
2. Apply display filter:

text
   bootp || tftp

3. If no DHCPDISCOVER frames arrive from the client's gateway IP, the Layer 3 switch is not relaying UDP broadcasts.

# Step-by-Step Fix:

1. Configure Dual IP Helper Commands on Switch VLAN Interface:

Access your Cisco/Aruba/Arista Layer 3 switch CLI and navigate to the client VLAN interface.

Add IP Helper statements pointing to both the DHCP server IP and the PXE/WDS server IP:

text
     interface Vlan10
      ip address 192.168.10.1 255.255.255.0
      ip helper-address 10.0.0.5   ! IP of Primary DHCP Server
      ip helper-address 10.0.0.10  ! IP of PXE / WDS Server

2. Verify UDP Forwarding Configuration:

Ensure UDP ports 67 (DHCP), 68 (DHCP Client), and 69 (TFTP) are explicitly permitted across inter-VLAN access control lists (ACLs).

3. Retest PXE Booting:

Power on the PXE client and confirm it receives a DHCP offer containing PXE server options.

# Prevention & Long-Term Monitoring:

Utilize IP Helpers rather than DHCP Options 66/67 when deploying Microsoft WDS or System Center Configuration Manager (SCCM), as IP Helpers allow dynamic architecture negotiation natively.

Hardcoded DHCP Options 66 and 67 Mismatch Across Legacy BIOS and UEFI Clients

Solution:

Root Cause: Static Option 67 NBP Path Incompatibility Across Boot Modes

Hardcoding DHCP Option 67 (Bootfile Name) with a single filename (e.g., boot\\x86\\wdsnbp.com for Legacy BIOS or boot\\x64\\wdsmgfw.efi for UEFI) causes instant PXE failures across heterogeneous client fleets. A UEFI client receiving a Legacy NBP file cannot execute the 16-bit real-mode binary and aborts. Conversely, a Legacy BIOS system receiving an EFI binary halts with a checksum error.

# Diagnostic Verification:

1. Open DHCP Server Console (dhcpmgmt.msc).
2. Inspect Scope Options and Server Options for statically defined Option 066 and Option 067.
3. Check PXE client boot mode: UEFI clients require boot\\x64\\wdsmgfw.efi (or bootx64.efi), while Legacy systems require boot\\x86\\wdsnbp.com (or undionly.kpxe).

# Step-by-Step Fix:

1. Remove Static Scope Options 66 and 67:

In Windows DHCP Server, right-click and delete Options 066 and 067 from both Scope Options and Server Options.

2. Create Vendor / Architecture Classes in Windows DHCP:

Right-click IPv4 > Select Define Vendor Classes.

Create policies based on DHCP Option 60 (PXEClient) Architecture Types:

Legacy BIOS: Architecture 00000 -> Assign Option 67 = boot\\x86\\wdsnbp.com

UEFI x64: Architecture 00007 or 00009 -> Assign Option 67 = boot\\x64\\wdsmgfw.efi

3. PowerShell Script to Create Dynamic DHCP Policies Automatically:

powershell
   # Add UEFI x64 Class Policy
   Add-DhcpServerv4Policy -Name "PXE_UEFI_x64" -ScopeId 192.168.10.0 -Condition OR -OptionId 60 -Value "PXEClient:Arch:00007*", "PXEClient:Arch:00009*"
   Set-DhcpServerv4OptionValue -PolicyName "PXE_UEFI_x64" -ScopeId 192.168.10.0 -OptionId 66 -Value "10.0.0.10"
   Set-DhcpServerv4OptionValue -PolicyName "PXE_UEFI_x64" -ScopeId 192.168.10.0 -OptionId 67 -Value "boot\\x64\\wdsmgfw.efi"

# Prevention & Long-Term Monitoring:

Refer to the Microsoft Official Support Guide for recommended PXE architecture policies.

Port 67 UDP Socket Collision (Co-located DHCP and WDS / PXE Server)

Solution:

Root Cause: UDP Port 67 Bind Conflict on Co-Located Infrastructure

Both standard DHCP services and PXE server listeners (e.g., Windows Deployment Services - WDS) bind to UDP Port 67 to process client broadcast messages. When both services run on the same Windows Server OS instance without special port-sharing configurations, WDS binds to UDP Port 67 first, preventing the DHCP service from listening or vice versa. The client receives standard IP configuration but no PXE vendor extensions.

# Diagnostic Verification:

1. Open PowerShell as Administrator on the co-located server.
2. Run netstat to check process IDs bound to UDP Port 67:

powershell
   Get-NetUDPEndpoint -LocalPort 67 | Select-Object LocalAddress, LocalPort, OwningProcess | Format-Table

3. If svchost.exe (DHCP) and wdssvc.exe (WDS) contend for port 67, option 60 proxying must be enabled.

# Step-by-Step Fix:

1. Configure WDS to Not Listen on Port 67:

Open WDS Console (wdsmgmt.msc).

Right-click your WDS server > Select Properties > Go to DHCP tab.

Check the box: Do not listen on DHCP ports (sets UseDHCPPorts = 0 in registry).

Check the box: Configure DHCP options to indicate that this is also a PXE server (sets Option 060 = PXEClient).

2. Command Line Fix via wdsutil:

cmd
   wdsutil /Set-Server /UseDHCPPorts:No /DHCPOption60:Yes

3. Restart Services:

cmd
   net stop wdssvc && net start wdssvc
   net stop dhcpserver && net start dhcpserver

# Prevention & Long-Term Monitoring:

Ensure Option 60 is strictly removed if WDS and DHCP are subsequently moved to separate dedicated servers.

proxyDHCP Offer Failure / Option 60 (PXEClient) Response Drop

Solution:

Root Cause: proxyDHCP Service Failing to Intercept Client Handshake

In environments using proxyDHCP (where a dedicated PXE server listens on UDP Port 4011 to provide bootloader paths while a standard DHCP server provides IP addresses on Port 67), the client must receive DHCP Option 60 (PXEClient) in the initial DHCP ACK. If Option 60 is omitted or if port 4011 is blocked by host firewalls, the PXE client ignores the secondary proxyDHCP offer and terminates the boot sequence.

# Diagnostic Verification:

1. Capture packets on the client subnet during boot.
2. Inspect the DHCP ACK packet sent from the primary DHCP server.
3. Verify if Option 60 (Vendor class identifier) contains the literal string PXEClient.

# Step-by-Step Fix:

1. Enable Option 60 on DHCP Scope:

Open DHCP Console (dhcpmgmt.msc).

Under Scope Options, add Option 060 with string value PXEClient.

2. Open Firewall Ports for proxyDHCP:

On the PXE / WDS server, execute PowerShell commands to allow UDP Port 4011:

powershell
     New-NetFirewallRule -DisplayName "PXE proxyDHCP UDP 4011 Inbound" -Direction Inbound -Action Allow -Protocol UDP -LocalPort 4011
     New-NetFirewallRule -DisplayName "PXE TFTP UDP 69 Inbound" -Direction Inbound -Action Allow -Protocol UDP -LocalPort 69

3. Restart PXE/proxyDHCP Service:

Restart your WDS, dnsmasq, or ConfigMgr PXE Responder service.

# Prevention & Long-Term Monitoring:

Verify that network security software does not strip DHCP Option 60 headers during active packet inspection.

What specific error code or behavior is displayed when the TFTP session fails?

Client displays 'PXE-E32: TFTP open timeout' after obtaining an IP address.
Client displays 'PXE-E38: TFTP read timeout' or hangs mid-transfer while downloading boot files.
TFTP returns 'File Not Found' or 'Access Violation' (Error Code 1 or 2).
TFTP download is extremely slow (taking 10+ minutes to load small boot images).

TFTP Port 69 UDP Packet Drop / Host Firewall Block

Solution:

Root Cause: Inbound UDP Port 69 Blockade or Asymmetric Return Path

TFTP (Trivial File Transfer Protocol) relies on UDP Port 69 to establish initial control handshakes. Once the request is received, the TFTP server dynamically allocates a high-numbered ephemeral UDP port (e.g., Port 49152+) to stream binary data. If Windows Defender Firewall or an intermediate network firewall blocks inbound UDP Port 69, or blocks ephemeral UDP return traffic, the PXE client times out at PXE-E32.

# Diagnostic Verification:

1. From a working client machine on the same subnet, test TFTP connectivity using the native Windows TFTP client:

Enable client: Enable-WindowsOptionalFeature -Online -FeatureName TFTP

Test download:

cmd
     tftp -i 10.0.0.10 GET boot\\x64\\boot.sdi C:\\test.sdi

2. If the command returns Timeout occurred or Connect request failed, UDP Port 69 is blocked.

# Step-by-Step Fix:

1. Create Firewall Exceptions on PXE / TFTP Server:

Run PowerShell as Administrator:

powershell
     New-NetFirewallRule -DisplayName "TFTP Service (UDP-In 69)" -Direction Inbound -Action Allow -Protocol UDP -LocalPort 69
     New-NetFirewallRule -DisplayName "WDS Executable Inbound" -Direction Inbound -Action Allow -Program "%SystemRoot%\\system32\\wdssvc.exe"

2. Configure Stateful Firewall Inspection for Dynamic TFTP Ports:

Ensure Windows Firewall 'Stateful FTP/TFTP' inspection is enabled so ephemeral ports opened by wdssvc.exe or tftpd32 are dynamically allowed.

3. Validate Routing and Path MTU:

Ensure no router access control list (ACL) drops inbound UDP traffic directed at the TFTP server IP.

# Prevention & Long-Term Monitoring:

Audit server firewall rules following Windows Server Cumulative Update installations.

TFTP Block Size Negotiation Mismatch / Path MTU Fragmentation Drops

Solution:

Root Cause: IP Packet Fragmentation Drops Triggered by Large TFTP Block Sizes

By default, standard TFTP uses a 512-byte block size. Modern PXE solutions (like WDS or SCCM) utilize TFTP Window Extension (Option 813) and expanded block sizes (e.g., 1456 or 16384 bytes) to accelerate file transfer speeds. If network routers or VPN tunnels between the PXE server and client enforce a lower Maximum Transmission Unit (MTU < 1500 bytes), TFTP packets fragment. Network firewalls often drop IP fragments, causing PXE-E38: TFTP read timeout drops mid-transfer.

# Diagnostic Verification:

1. Capture TFTP traffic in Wireshark during PXE boot.
2. Look for Option Acknowledgement (OACK) packets sent by the server specifying blksize: 1456 followed by ICMP Destination Unreachable (Fragmentation Needed) messages from intermediate routers.

# Step-by-Step Fix:

1. Adjust WDS TFTP Block Size via Registry:

Open Registry Editor (regedit.exe) on the WDS Server.

Navigate to:

HKLM\\SYSTEM\\CurrentControlSet\\Services\\WDSServer\\Providers\\WDSTFTP

Create / Modify DWORD value ReadFilter = 1

Create / Modify DWORD value BmtWindowSize = 1 or 4

Create / Modify DWORD value MaximumBlockSize = 1456 (or lower down to 512 if traversing routed subnets).

2. Command Line Registry Fix:

cmd
   reg add "HKLM\\SYSTEM\\CurrentControlSet\\Services\\WDSServer\\Providers\\WDSTFTP" /v MaximumBlockSize /t REG_DWORD /d 1456 /f

3. Restart WDS Service:

cmd
   net stop wdssvc && net start wdssvc

# Prevention & Long-Term Monitoring:

Keep TFTP block size set to 1456 bytes for enterprise networks to prevent IP fragmentation across standard Ethernet MTU (1500 byte) boundaries.

Incorrect NBP Relative File Pathing / NTFS Permission Lock on TFTP Root

Solution:

Root Cause: Absolute vs Relative TFTP Path Misconfiguration or Access Control Denied

TFTP daemons operate within a strict virtual root folder (e.g., C:\\RemoteInstall or /var/lib/tftpboot). If DHCP Option 67 or PXE bootloader configuration files reference absolute paths (e.g., C:\\RemoteInstall\\boot\\x64\\wdsmgfw.efi) instead of paths relative to the TFTP root (boot\\x64\\wdsmgfw.efi), the TFTP server throws Error 1: File Not Found. Furthermore, if the SERVICE or EVERYONE account lacks read permissions on the boot folder, TFTP returns Error 2: Access Violation.

# Diagnostic Verification:

1. Open WDS Event Viewer: Event Viewer > Applications and Services Logs > Microsoft > Windows > Deployment-Services-Diagnostics.
2. Search for Event ID 256 or 513 indicating missing files or read permission failures on RemoteInstall paths.

# Step-by-Step Fix:

1. Correct Path Format in DHCP Option 67:

Ensure backward slashes or forward slashes conform to server OS standards:

Windows WDS: boot\\x64\\wdsmgfw.efi (no leading backslash).

Linux tftpd: boot/x64/bootx64.efi

2. Fix NTFS Read Permissions on TFTP Root:

Open Command Prompt as Administrator and reset ACLs on the WDS root folder:

cmd
     icacls "C:\\RemoteInstall" /grant "READERS":(OI)(CI)R /T
     icacls "C:\\RemoteInstall" /grant "NETWORK SERVICE":(OI)(CI)F /T

3. Verify WDS Root Registry Path:

Confirm HKLM\\SYSTEM\\CurrentControlSet\\Services\\WDSServer\\Providers\\WDSTFTP\\RootPath points correctly to C:\\RemoteInstall.

# Prevention & Long-Term Monitoring:

Never store boot files outside the designated TFTP root directory.

TFTP Single-Block Window Acknowledgment Latency Bottleneck

Solution:

Root Cause: Lack of TFTP Windowing / Single Packet Lockstep Acknowledgment

Standard legacy TFTP transfers data using a lockstep mechanism: the server sends block 1, waits for the client ACK, sends block 2, waits for ACK. Over high-latency routed subnets (or Wi-Fi / WAN links), this latency delay accumulates, causing 300MB WinPE boot images to take over 15 minutes to download.

# Diagnostic Verification:

1. Monitor PXE boot: Progress bar moves extremely slowly, transferring a few kilobytes per second despite gigabyte network links.

# Step-by-Step Fix:

1. Enable TFTP Variable Window Size (Option 743 / WDS Windowing):

Enable variable window size so the server transmits multiple UDP packets before requiring a client ACK.

2. PowerShell Command to Enable WDS Variable Windowing:

powershell
   Set-ItemProperty -Path "HKLM:\\SYSTEM\\CurrentControlSet\\Services\\WDSServer\\Providers\\WDSTFTP" -Name "EnableVariableWindowSize" -Value 1

3. Adjust TFTP Window Size:

powershell
   Set-ItemProperty -Path "HKLM:\\SYSTEM\\CurrentControlSet\\Services\\WDSServer\\Providers\\WDSTFTP" -Name "BmtWindowSize" -Value 8

4. Restart WDS Service:

cmd
   net stop wdssvc && net start wdssvc

# Prevention & Long-Term Monitoring:

Test TFTP transfer speeds on remote subnets whenever new network switches or WAN routers are deployed.

What error or failure mode occurs after the Network Boot Program (NBP) successfully downloads?

UEFI system downloads `wdsnbp.com` or 16-bit NBP, displays 'NBP file downloaded successfully', and reboots immediately.
UEFI Secure Boot blocks execution of unassigned iPXE / custom NBP binaries with a Security Violation screen.
PXE client downloads `pxelinux.0` / `syslinux`, but fails to locate configuration files (`pxelinux.cfg/default`).
WDS displays 'Press F12 for Network Service Boot', but times out and boots local drive.

Architecture Mismatch: Executing 16-Bit Real-Mode NBP on Native 64-Bit UEFI Firmware

Solution:

Root Cause: Loading Legacy Real-Mode Bootloaders on Native UEFI Hardware

wdsnbp.com and pxelinux.0 are 16-bit real-mode binaries designed exclusively for Legacy BIOS / CSM (Compatibility Support Module) environments. Modern native UEFI firmware lacks 16-bit BIOS interrupt vectors (INT 10h, INT 13h). When a UEFI system downloads wdsnbp.com, execution fails immediately upon kernel entry, causing the system to drop execution and reboot.

# Diagnostic Verification:

1. Check client System Setup / BIOS: Boot Mode is set to UEFI (CSM Disabled).
2. Inspect DHCP Option 67 value delivered to client: Option 67 specifies wdsnbp.com or undionly.kpxe instead of wdsmgfw.efi or ipxe.efi.

# Step-by-Step Fix:

1. Update DHCP Bootfile Path for UEFI Clients:

Change Option 67 / Policy Target to point to native 64-bit EFI bootloaders:

Microsoft WDS / SCCM: boot\\x64\\wdsmgfw.efi

iPXE Open Source: ipxe.efi or snponly.efi

Linux / iPXE: grubx64.efi or bootx64.efi

2. Configure WDS Default NBP for Architecture Types:

Run Command Prompt as Administrator on WDS Server:

cmd
     wdsutil /Set-Server /BootProgram:boot\\x64\\wdsmgfw.efi /Architecture:x64
     wdsutil /Set-Server /NbdBootProgram:boot\\x64\\wdsmgfw.efi /Architecture:x64
     wdsutil /Set-Server /BootProgram:boot\\x86\\wdsnbp.com /Architecture:x86

3. Restart WDS Service (net stop wdssvc && net start wdssvc).

# Prevention & Long-Term Monitoring:

Phase out Legacy BIOS configurations and transition all enterprise imaging scopes to native UEFI x64 bootloaders.

UEFI Secure Boot Signature Verification Failure

Solution:

Root Cause: Untrusted Digital Signature on Custom PXE Bootloaders

UEFI Secure Boot validates the Microsoft Third-Party UEFI CA digital signature embedded within the NBP binary PE/COFF header before execution. Open-source or custom-compiled bootloaders (such as un-signed iPXE binaries, custom GRUB builds, or legacy Linux kernels) lack a valid Microsoft CA signature. UEFI Secure Boot halts execution instantly with a security violation error.

# Diagnostic Verification:

1. Client displays red warning box: Secure Boot Violation - Invalid Signature Detected or Selected boot device failed verification.

# Step-by-Step Fix:

1. Use Microsoft-Signed Bootloaders:

For WDS / SCCM, ensure wdsmgfw.efi is used (signed natively by Microsoft Windows Production PCA).

For Linux / iPXE deployment, use official distribution-signed shimx64.efi or signed ipxe.efi builds.

2. Temporarily Disable Secure Boot in Target Client BIOS (for testing/custom images):

Enter system setup (F2 / Del).

Navigate to Security > Secure Boot.

Set Secure Boot = Disabled.

Save and reboot (F10).

3. Enroll Custom Machine Owner Key (MOK) if using custom Linux kernels:

Import your custom signing key into the system MOK database using mokutil on Linux boot.

# Prevention & Long-Term Monitoring:

Ensure all custom PXE binaries deployed across enterprise subnets are signed using an enrolled MOK or official vendor certificate.

Syslinux / PXELINUX Configuration File Path Resolution Failure

Solution:

Root Cause: Missing MAC / IP Specific Configuration Files in pxelinux.cfg\n\nWhen pxelinux.0 executes, it attempts to query the TFTP server for specific configuration files under the pxelinux.cfg/ directory using hexadecimal IP representations (e.g., C0A80A05) or MAC addresses (e.g., 01-88-99-aa-bb-cc-dd), falling back finally to pxelinux.cfg/default. If the TFTP server lacks the default file or if case-sensitive Linux filesystems fail to locate PXELINUX.CFG, execution stalls.\n\n#### Diagnostic Verification:\n1. Inspect TFTP server access logs (/var/log/syslog or TFTPd GUI log).\n2. Observe repeated 404 File Not Found requests for pxelinux.cfg/01-xx-xx-xx-xx-xx-xx ending with missing pxelinux.cfg/default.\n\n#### Step-by-Step Fix:\n1. Create default Configuration File:\n * Inside the TFTP root, ensure directory pxelinux.cfg/ exists in lowercase.\n * Create a file named default (no extension) with valid boot entry syntax:\n

text\n     DEFAULT menu.c32\n     PROMPT 0\n     TIMEOUT 300\n     ONTIMEOUT local\n     LABEL winpe\n         MENU LABEL Boot Windows PE\n         KERNEL memdisk\n         INITRD boot/winpe.iso\n         APPEND iso raw\n

\n2. Fix Case-Sensitivity Permissions on Linux TFTP Servers:\n

bash\n   chmod -R 755 /var/lib/tftpboot/pxelinux.cfg\n   chown -R tftp:tftp /var/lib/tftpboot\n

\n\n#### Prevention & Long-Term Monitoring:\n* Verify that all sub-directories under TFTP root strictly adhere to lowercase naming conventions on Linux hosts.

WDS F12 Prompt Timeout / Mandatory PXE Boot Requirement

Solution:

Root Cause: Unattended PXE Execution Blocked by F12 User Prompt Requirement

By default, Windows Deployment Services requires an operator to physically press F12 on the client keyboard within a 10-second window when wdsnbp.com loads. If unattended automated OS deployments (such as automated SCCM task sequences or bare-metal provisioning) run overnight, the prompt times out and the system boots to the local hard drive.

# Diagnostic Verification:

1. Client screen displays: Press F12 for network service boot.
2. No key is pressed; system bypasses PXE after 10 seconds and attempts local drive boot.

# Step-by-Step Fix:

1. Configure WDS to Architecture-Level Architecture Abort Override:

Open WDS Console (wdsmgmt.msc).

Right-click WDS Server > Select Properties > Go to Boot tab.

Under PXE Boot Policy, set both Known and Unknown clients to:

Always continue the PXE boot.
2. Execute wdsutil Command Line Override:

cmd
   wdsutil /Set-Server /PxePromptPolicy /Known:NoPrompt /UnKnown:NoPrompt

3. Use Architecture-Specific NBP for Direct Booting:

Change boot program to boot\\x64\\hdlsmgfw.efi (or boot\\x86\\pxeboot.com), which bypasses the F12 key requirement automatically.

# Prevention & Long-Term Monitoring:

Ensure PXE boot priority in system BIOS is placed after local storage in production to prevent infinite PXE boot loops once provisioning completes.

What error code or crash behavior occurs during WinPE / RAMDISK image downloading?

WinPE loading bar hangs indefinitely while downloading `boot.wim` via BCD / WIM bootloader.
System displays BSOD error '0xc000000f: The boot selection failed because a required device is inaccessible'.
WinPE boots successfully, but crashes with 'Wpeinit failed with status 0x80070002' or missing network driver error.
System displays BSOD error '0xc0000001: Required file is missing or contains errors' during RAMDISK load.

WinPE RAMDISK TFTP Window Size Bottleneck / Network Driver Stall

Solution:

Root Cause: WIM Download Stall via Unbuffered RAMDISK TFTP Streaming

Once wdsmgfw.efi loads, it processes the Boot Configuration Data (BCD) file to download the Windows Preinstallation Environment image (boot.wim) into system RAM via RAMDISK. If the client NIC driver or physical switch port exhibits flow control errors or drop buffers during high-speed RAMDISK streaming, the download progress bar freezes at 0% or random percentage points.

# Diagnostic Verification:

1. Screen displays: Loading files... \\windows\\system32\\boot.win with progress bar frozen.
2. Switch port status shows high numbers of Rx/Tx pause frames or CRC alignment errors.

# Step-by-Step Fix:

1. Increase Ramdisk TFTP Block Size and Window Size in BCD Store:

Open Command Prompt as Administrator on WDS/SCCM server.

Edit the active BCD store used for PXE booting:

cmd
     bcdedit /store C:\\RemoteInstall\\boot\\x64\\default.bcd /set {ramdiskoptions} ramdisktftpblocksize 1456
     bcdedit /store C:\\RemoteInstall\\boot\\x64\\default.bcd /set {ramdiskoptions} ramdisktftpwindowsize 8

2. Disable Flow Control on Switch Ports:

Disable Ethernet Flow Control (802.3x) on the access switch port connected to the PXE client.

3. Update Client NIC Firmware:

Ensure motherboard embedded network controllers have up-to-date Option ROM / NVM firmware.

# Prevention & Long-Term Monitoring:

Avoid setting ramdisktftpblocksize above 1456 bytes to guarantee safe packet traversal across routed enterprise networks.

Corrupted Boot Configuration Data (BCD) / BCD Store Path Resolution Error (0xc000000f)

Solution:

Root Cause: Missing or Corrupted BCD Store Pointer to boot.wim GUID

Error 0xc000000f during the PXE RAMDISK initialization phase indicates that wdsmgfw.efi successfully downloaded, but the BCD store file (\\boot\\x64\\default.bcd) contains invalid object GUID pointers or hardcoded drive paths (e.g., device ramdisk=[boot]\\boot\\boot.wim) that do not match the TFTP directory structure.

# Diagnostic Verification:

1. Client screen displays Windows Boot Manager error:
Status: 0xc000000f - Info: The boot selection failed because a required device is inaccessible.

# Step-by-Step Fix:

1. Rebuild WDS / PXE BCD Store:

Open Command Prompt as Administrator on WDS server.

Stop WDS Service: net stop wdssvc

Backup existing BCD file:

cmd
     ren C:\\RemoteInstall\\boot\\x64\\default.bcd default.bcd.bak

2. Re-create Clean BCD Store using WDS Utility:

cmd
   wdsutil /Uninitialize-Server
   wdsutil /Initialize-Server /REMOUNT /Folder:C:\\RemoteInstall

3. Manually Update BCD Objects if using custom PXE Server:

cmd
   bcdedit /store C:\\tftpboot\\boot.bcd /set {default} device ramdisk=[boot]\\boot\\boot.wim,{ramdiskoptions}
   bcdedit /store C:\\tftpboot\\boot.bcd /set {default} osdevice ramdisk=[boot]\\boot\\boot.wim,{ramdiskoptions}

4. Restart WDS Service (net stop wdssvc).

# Prevention & Long-Term Monitoring:

Always use the official WDS Management Console to update boot images rather than manually replacing boot.wim files inside the file system.

WinPE Missing Network Interface Card (NIC) Drivers / Wpeinit Status 0x80070002

Solution:

Root Cause: Unbound Network Stack inside Windows PE Environment

WinPE boots into a minimal kernel state and runs wpeinit.exe to initialize network adapters and query DHCP. If the boot.wim image lacks the specific NDIS network driver for the client's physical Ethernet chipset (e.g., modern Intel I225-V, Realtek 2.5GbE, or USB-C Ethernet dongles), wpeinit fails to obtain an IP address and aborts with 0x80070002 or a blank command prompt.

# Diagnostic Verification:

1. Once WinPE displays the command prompt or error, press Shift + F10 to open a console window.
2. Run ipconfig /all.
3. If no Ethernet adapters are listed (or only Loopback 127.0.0.1 appears), WinPE lacks the required network driver.

# Step-by-Step Fix:

1. Obtain Out-of-Band WinPE Driver Pack:

Download the official WinPE Driver Pack from your OEM vendor (e.g., Dell Command Deploy WinPE Driver Pack, HP WinPE Pack, or Lenovo WinPE Pack).

2. Inject Driver into boot.wim using DISM:

Open PowerShell as Administrator on your management workstation:

powershell
     # Mount WinPE Image
     Mount-WindowsImage -Path "C:\\mount" -ImagePath "C:\\RemoteInstall\\Boot\\x64\\Images\\boot.wim" -Index 1
     
     # Inject Drivers Recursively
     Add-WindowsDriver -Path "C:\\mount" -Driver "C:\\WinPE_Drivers" -Recurse
     
     # Save and Unmount
     Dismount-WindowsImage -Path "C:\\mount" -Save

3. Refresh WDS / PXE Boot Image:

Restart WDS Service to propagate the updated boot.wim across TFTP distribution points.

# Prevention & Long-Term Monitoring:

Maintain a centralized driver repository and inject updated network drivers into WinPE boot images biannually.

WinPE RAMDISK Corrupted File Hash / Physical Memory Fault (0xc0000001)

Solution:

Root Cause: Memory Corruption During RAMDISK Extraction or Truncated WIM File

Error 0xc0000001 during the WinPE RAMDISK loading phase indicates that the downloaded boot.wim file failed digital hash or checksum verification in memory. This is caused by either a truncated file transfer across TFTP (file size on server does not match file size in RAM) or defective physical System RAM (DRAM) on the client machine failing during heavy RAMDISK allocation.

# Diagnostic Verification:

1. Client displays Windows Recovery Error: Status: 0xc0000001 - Info: A required device isn't connected or can't be accessed.
2. Verify the size of boot.wim on the TFTP server against the bytes received by the client in Wireshark packet captures.

# Step-by-Step Fix:

1. Re-export and Replace boot.wim on PXE Server:

Verify that the source boot.wim is not corrupted on the server storage array.

Re-copy a clean boot.wim from official Windows ADK / ISO installation media to the WDS server.

2. Run MemTest86 on Client Hardware:

Boot the target client using a bootable USB containing MemTest86 to check for bad memory blocks in physical DRAM.

3. Verify Client RAM Allocation:

Ensure the target client has at least 4GB of physical RAM installed to accommodate the RAMDISK expansion footprint.

# Prevention & Long-Term Monitoring:

Perform periodic MD5/SHA256 checksum validation on boot images stored across distributed PXE server nodes.

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