Network booting or net boot is the process of booting a computer from a network location rather than a local
drive. Most commonly, a boot file is an encapsulated image or snapshot, of an operating system (OS) and
configuration. A “zip file” is a similar type of container; it’s a specific file format that contains a variable
data payload. In this case, the boot file’s payload would be an OS and configuration thus containing anything
the device would need upon booting up to proceeding past a Power On Self-Test (POST). In theory, file formats
can include anything that can be downloaded via TFTP and processed/executed by the Network Card's PXE stack.
Below is diagram depicting
the actual boot process of the PXE.
As of firmware version 1.03.16 you now have the option to use the server IP address
(siaddr) field in the Dynamic Host Configuration Protocol (DHCP) header – called the
Next Server field and the file field – titled filename. This field is your
boot file or image. For further context see RFC 2131 (Link to view RFC).
So why would you want to use network booting? When using network booting across many workstations, it can
streamline the process in disk imaging solutions.
Additional use cases for this feature include:
Keeping automated kiosks or terminals updated (like movie ticket dispensers)
Provisioning of multiple workstations via network
SMB Cisco devices attached to an enterprise network currently utilizing net booting
Why use Network Boot when we have DHCP Option 66?
Net boot much like Option 66 allows for a remote image to be provided to an endpoint. If you needed to provide
different images to the same devices on the same Virtual Local Area Network (VLAN), you could do that with both
Net Boot and DHCP Option 66. In that sense, the features are complimentary.
Additionally, using a DHCP server as a network boot location was not what DHCP was meant for and this adds
complexity to your network. Especially when attempting to serve network booting to multiple hardware platforms.
Note: Not all PXE clients will properly interpret DHCP Option 150 as it is Cisco proprietary;
so, if possible Option 66 should be used.
Steps to Configure Network Booting
Step 1. After logging into your device, click LAN > VLAN Settings items from the
Note: Don’t see the menu sidebar? The menu-sidebar may be in a collapsed state. Try clicking the
button in the upper-left hand corner. Example below:
Step 2. In the VLAN Table, click the checkbox to the left of the VLAN you intend to
direct to the PXE boot, then click the Edit button. In our case we selected the default
Step 3. Click the checkbox next to Network Booting to Enable it. Then input your
Next Server IP address and Boot File name.
*.CMD and *.EFI - Windows Deployment Services for OS installs
*.BIN - Citrix vDisk boot
*.KPXE - FOG disk imaging
*.XML - Remote Hypervisor booting, generally requires specific firmware/bios options and mostly
Note:.Com files are also accepted, as depicted in the screenshot, though they may be less
Step 4. Click the Apply button.
Note: If you wish to save this configuration between boots, be sure to click the blinking save
icon in the upper portion of the screen.
Verifying Configuration via Wireshark
The below screenshot displays where to find the Next Server and Boot file fields in the DHCP offer from
If you run into errors after the client receives the DHCP Proxy request acknowledgement from the PXE
server, we are unable to assist directly with those issues. From that point forward try testing the PXE server
as well as basic IP connectivity or the PXE Client itself. If the PXE server is on the same VLAN, the PXE client
makes its Address Resolution Protocol (ARP) requests for the PXE server. Otherwise PXE servers located outside
of the VLAN will be directed to the default gateway.