Administrator Guide

DHCP and USB Auto-Configuration 551
• Domain Name - Option 15
• NTP Server - Option 42
When a DHCP OFFER identifies the TFTP server more than once, the
DHCP client selects one of the options in the following order: sname, option
66, option 150, siaddr. If the TFTP server is identified by hostname, a DNS
server is required to translate the name to an IP address.
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 as noted below.
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 a USB drive, or
even with a saved configuration file that has Auto Configuration enabled.
The network DHCP server may return 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 with sub-option 5, 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.
For example, one might enter the following information:
• A2-02-00-00 — Dell Enterprise number 674. It should be written from
right to left. The number 674 in hexadecimal notation is 02 a2 00 00.
• 0c — Data Length (12 decimal)
• 05 — Sub-option code 5
• 0a — Sub-option length (10 decimal)
• Conversion of the file name from ACSII to hexadecimal:
"Config.txt" – 43-6F-6E-66-69-67-2E-74-78-74
The Config.txt file should contain the full name of the image file on the
TFTP server, including the relative path name, e.g.,
N3000_N2000v6.3.0.1.stk