DHCP Auto-Image Update
You can use DHCP auto-image upgrade with DHCP autoconfiguration to download both a configuration and
a new image to one or more devices in your network. The devices (or devices) downloading the new
configuration and the new image can be blank (or only have a default factory configuration loaded).
If the new configuration is downloaded to a switch that already has a configuration, the downloaded
configuration is appended to the configuration file stored on the switch. (Any existing configuration is not
overwritten by the downloaded one.)
To enable a DHCP auto-image update on the device, the TFTP server where the image and configuration files
are located must be configured with the correct option 67 (the configuration filename), option 66 (the DHCP
server hostname) option 150 (the TFTP server address), and option 125 (description of the Cisco IOS image
file) settings.
After you install the device in your network, the auto-image update feature starts. The downloaded configuration
file is saved in the running configuration of the device, and the new image is downloaded and installed on the
device. When you reboot the device, the configuration is stored in the saved configuration on the device.
DHCP Server Configuration Guidelines
Follow these guidelines if you are configuring a device as a DHCP server:
• You should configure the DHCP server with reserved leases that are bound to each device by the device
hardware address.
• If you want the device to receive IP address information, you must configure the DHCP server with these
lease options:
• IP address of the client (required)
• Subnet mask of the client (required)
• DNS server IP address (optional)
• Router IP address (default gateway address to be used by the device) (required)
• If you want the device to receive the configuration file from a TFTP server, you must configure the
DHCP server with these lease options:
• TFTP server name (required)
• Boot filename (the name of the configuration file that the client needs) (recommended)
• Hostname (optional)
• Depending on the settings of the DHCP server, the device can receive IP address information, the
configuration file, or both.
• If you do not configure the DHCP server with the lease options described previously, it replies to client
requests with only those parameters that are configured. If the IP address and the subnet mask are not in
the reply, the device is not configured. If the router IP address or the TFTP server name are not found,
the device might send broadcast, instead of unicast, TFTP requests. Unavailability of other lease options
does not affect autoconfiguration.
• The device can act as a DHCP server. By default, the Cisco IOS DHCP server and relay agent features
are enabled on your device but are not configured. (These features are not operational.)
System Management Configuration Guide, Cisco IOS XE Amsterdam 17.2.x (Catalyst 9500 Switches)
54
Performing Device Setup Configuration
DHCP Auto-Image Update
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