Dell M6220 User Configuration Manual page 359

The DHCP client on the switch also processes the name of the text file
(option 125, the V-I vendor-specific Information option) which contains the
path to the image file.
Obtaining the Image
Auto Configuration attempts to download an image file from a TFTP server
only if no configuration file was found in the internal flash, or even with a
saved configuration file that has Auto Configuration enabled.
The network DHCP server returns a DHCP OFFER message with option
125. When configuring the network DHCP server for image downloads, you
must include Option 125 and specify the Dell Enterprise Number, 674.
Within the Dell section of option 125, sub option 5 must specify the path and
name of a file on the TFTP server. This file is not the image file itself, but
rather a text file that contains the path and name of the image file. Upon
receipt of option 125, the switch downloads the text file from the TFTP
server, reads the name of the image file, and downloads the image file from
the TFTP server.
After the switch successfully downloads and installs the new image, it
automatically reboots. The download or installation might fail for one of the
following reasons:
• The path or filename of the image on the TFTP server does not match the
information specified in DHCP option 125.
• The downloaded image is the same as the current image.
• The validation checks, such as valid CRC Checksum, fails.
If the download or installation was unsuccessful, a message is logged.
NOTE:
In stack of switches, the downloaded image is pushed to all members
attached to the stack at the time of download. For members who join the stack
after the download, the Stack Firmware Synchronization feature will push the
latest image to all members.
Auto Image and Configuration Update
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