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Catalyst 3750 SwitchSoftware Configuration Guide
OL-8550-09
Chapter3 Assigning the Switch IP Address and Default Gateway
Assigning Switch Information
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 switches in your network. The switch (or switches) 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.)
Note To enable a DHCP auto-image update on the switch, 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
file) settings.
For procedures to configure the switch as a DHCP server, see the “Configuring DHCP-Based
Autoconfiguration” section on page3-7 and the “Configuring DHCP” section of the “IP addressing and
Services” section of the Cisco IOS IP Configuration Guide, Release12.2.
After you install the switch in your network, the auto-image update feature starts. The downloaded
configuration file is saved in the running configuration of the switch, and the new image is downloaded
and installed on the switch. When you reboot the switch, the configuration is stored in the saved
configuration on the switch.
Limitations and Restrictions
These are the limitations:
•The DHCP-based autoconfiguration with a saved configuration process stops if there is not at least
one Layer 3 interface in an up state without an assigned IP address in the network.
•Unless you configure a timeout, the DHCP-based autoconfiguration with a saved configuration
feature tries indefinitely to download an IP address.
•The auto-install process stops if a configuration file cannot be downloaded or it the configuration
file is corrupted.
Note The configuration file that is downloaded from TFTP is merged with the existing configuration in the
running configuration but is not saved in the NVRAM unless you enter the write memory or
copy running-configuration startup-configuration privileged EXEC command. Note that if the
downloaded configuration is saved to the startup configuration, the feature is not triggered during
subsequent system restarts.