Pxe Boot Process Flow - Cisco Catalyst 4500 Series Software Configuration Manual

Chapter 6 Programmability
Observe the following DHCP server configuration guidelines:
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PXE Boot Process Flow

This section outlines the communication process between the DHCP server and the switch and provides
the sequence of events followed during the PXE boot (network boot loading) process. This assumes that
autoboot is enabled.
You must provide the gateway, subnet mask, server IP address, and the client IP address. This
information is not permanently stored on switch. They are used only to download files and are
deleted when the activity is complete.
Specifics for the start-up configuration file, script file and ova files (applies to DHCP server
configuration for Microsoft Windows and Linux):
Complete the DHCP Option 43 list with information about the location of configuration, script
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and ova file to be downloaded.
You can specify an HTTP server or a TFTP server location from which to download. Depending
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on your requirement, specify one or more options— the boot image name, the start-up
configuration file name and path, the script file name and path, and the ova file name and path.
Ensure that the configuration, script and ova file extensions are
<config-file>.config,<script-file>.script,<container-file>.ova
– If you are opting for Zero-Touch Provisioning, the ova file name must include _dmi_. For
example,
example_dmi_container.ova
– These files should be saved in the root folder.
– If you are using HTTP to download, you must configure the DNS server information.
When the DHCP server responds successfully, the output displays
If you receive a TFTP timeout error, increase the DHCP timeout by using the ROMMON variable
DhcpTimeout. The default DHCP timeout is 5 seconds. You can increase it by a maximum of 30
seconds. For example, if DhcpTimeout=20, the DHCP timeout increases by 20 seconds. Enter the
set command to verify the change.
rommon> DhcpTimeout=20
rommon> set
The DHCP options list that the DHCP server sends should not be greater than 255 bytes. If it is, the
following error message is displayed:
DHCP ERROR: Received Option length is more than maximum supported (255)
The PXE process ignores network information that you configure on the ROMMON, such as IP,
gateway, subnet mask etc.
You can interrupt the autoboot process at any point, by pressing Control +C (switches to the
ROMMON mode).
– For sample output of the autoboot process, using HTTP, see
HTTP, page 6-37.
For sample output of the autoboot process using TFTP, see
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TFTP, page 6-40
The switch sends a DHCP discovery packet.
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The DHCP server responds with an offer containing the TFTP or HTTP server IP address, the
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offered IP address for the client, the gateway IP address, the boot file name, and the path and
names of the OVA, script, and switch configuration files.
Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
Configuring Programmability Components
respectively.
Received DHCP_ACK.
Autoboot Process Output—Using
Autoboot Process Output—Using
6-7