PowerOn Auto Provisioning (POAP) automates the process of
upgrading software images and installing configuration files on
Cisco Nexus switches that are being deployed in the network for the first time.
When a Cisco Nexus Series switch with the POAP feature boots and does not
find the startup configuration, the switch enters POAP mode, locates a DHCP server, and bootstraps itself with its interface IP address, gateway, and DNS server IP addresses. The switch also obtains the IP address of a TFTP server or the URL of an HTTP server and downloads a configuration script that enables the
switch to download and install the appropriate software image and
The DHCP information is used only during the POAP process.
If a USB (Universal Serial Device) device that contains the required installation files is not available, POAP requires the following network infrastructure:
A DHCP server to bootstrap the interface IP address, gateway address, and DNS (Domain Name System) server.
A TFTP server that contains the configuration script used to automate the software image installation and configuration process.
One or more servers that contains the desired software images and configuration files.
Figure 1. POAP Network Infrastructure
The reference script
supplied by Cisco supports the following functionality:
switch-specific identifier, for example, the serial number.
software image (system and kickstart images) if the files do not already exist
on the switch. The software image is installed on the switch and is used at the
downloaded configuration to be applied at the next switch reboot.
configuration as the startup configuration.
Cisco has sample
configuration scripts that were developed using the Python programming language
and Tool Command Language (Tcl). You can customize one of these scripts to meet
the requirements of your network environment.
For Cisco Nexus 7000
Series devices, the Python programming language uses two APIs that can execute
CLI commands. These APIs are described in the following table. The arguments
for these APIs are strings of the CLI commands.
raw output of CLI commands, including the control/special characters.
commands that support XML, this API puts the command output in a Python
This API can
be useful to help search the output of
The POAP process has the following phases:
Within these phases, other process and decision points occur. The following illustration shows a flow diagram of the POAP process.
When you power up a
switch for the first time, it loads the software image that is installed at
manufacturing and tries to find a configuration file from which to boot. When a
configuration file is not found, POAP mode starts.
During startup, a
prompt appears asking if you want to abort POAP and continue with a normal
setup. You can choose to exit or continue with POAP.
No user intervention
is required for POAP to continue. The prompt that asks if you want to abort
POAP remains available until the POAP process is complete.
If you exit POAP
mode, you enter the normal interactive setup script. If you continue in POAP
mode, all the front-panel interfaces are set up in the default configuration.
The switch sends out
DHCP discover messages on the MGMT interface that solicits DHCP offers from the
DHCP server or servers. (See the following figure.) The DHCP client on the
Cisco Nexus switch uses the switch serial number in the client-identifier
option to identify itself to the DHCP server. The DHCP server can use this
identifier to send information, such as the IP address and script filename,
back to the DHCP client.
POAP requires a
minimum DHCP lease period of 3600 seconds (1 hour). POAP checks the DHCP lease
period. If the DHCP lease period is set to less than 3600 seconds (1 hour),
POAP does not complete the DHCP negotiation.
The DHCP discover
message also solicits the following options from the DHCP server.
TFTP server name
or TFTP server address—The DHCP server relays the TFTP server name or TFTP
server address to the DHCP client. The DHCP client uses this information to
contact the TFTP server to obtain the script file.
DHCP server relays the bootfile name to the DHCP client. The bootfile name
includes the complete path to the bootfile on the TFTP server. The DHCP client
uses this information to download the script file.
When multiple DHCP
offers that meet the requirement are received, an offer is randomly chosen. The
device completes the DHCP negotiation (request and acknowledgment) with the
selected DHCP server, and the DHCP server assigns an IP address to the switch.
If a failure occurs in any of the subsequent steps in the POAP process, the IP
address is released back to the DHCP server.
If no DHCP offers meet
the requirements, the switch does not complete the DHCP negotiation (request
and acknowledgment) and an IP address is not assigned.
Figure 3. DHCP Discovery
Script Execution Phase
After the device bootstraps itself using the information in the DHCP acknowledgement, the script file is downloaded from the TFTP server.
The switch runs the configuration script, which downloads and
installs the software image and downloads a switch-specific
However, the configuration file is not applied to the switch at
this point, because the software image that currently runs on the
switch might not support all of the commands in the configuration
file. After the switch reboots, it begins running the new software
image, if an image was installed. At that point, the configuration is
applied to the switch.
If the switch loses connectivity, the script stops, and
the switch reloads its original software images and bootup
Post-Installation Reload Phase
The switch restarts and applies (replays) the configuration on the upgraded software image. Afterward, the switch copies the running configuration to the startup configuration.
Guidelines and Limitations for POAP
POAP configuration guidelines and limitations are as follows:
Cisco Nexus switch software image must support POAP for this feature to
POAP does not support provisioning of the switch
after it has been configured and is operational. Only auto-provisioning of a switch with no startup configuration is
If you use POAP to bootstrap a Cisco
Nexus device that is a part of a vPC (virtual port channel) pair using static
port channels on the vPC links, the Cisco Nexus device activates
all of its links when POAP starts up. The dually connected device at
the end of the vPC links might start sending some or all of its
traffic to the port-channel member links that are connected to the Cisco
Nexus device, which causes traffic to get lost.
To work around this issue, you can
configure the Link Aggregation Control Protocol (LACP) on the vPC links so that the links do not
incorrectly start forwarding traffic to the Cisco Nexus device that
is being bootstrapped using POAP.
If you use POAP to bootstrap a Cisco Nexus device that is connected downstream to a Cisco Nexus 7000 Series
device through a LACP port channel, the Cisco Nexus 7000
Series device defaults to suspend its member port if it cannot bundle
it as a part of a port channel. To work around this issue,
configure the Cisco Nexus 7000 Series device to not suspend its
member ports using the no lacp suspend-individual command from
interface configuration mode.
Important POAP updates
are logged in the syslog and are available from the serial
Critical POAP errors are
logged to the bootflash. The filename format is date-time _poap_PID_[init,1,2].log, where date-time is in the YYYYMMDD_hhmmss format and PID is the process ID.
Script logs are saved in the bootflash directory. The filename format is date-time_poap_PID_script.log, where date-time is in the YYYYMMDD_hhmmss format and PID is the process ID.
You can configure the format of the script log file. Script file log formats are specified in the script. The template of the script log file has a default format; however, you can choose a different format for the script execution log file.
The POAP feature does not require a license and is enabled by default. However for the POAP feature to function, appropriate licenses must be installed on the devices in the network before the deployment of the network.
To allow the POAP feature to function temporarily without the installation of the appropriate licenses, you can specify the license grace-period command in the configuration file.
This workaround allows you to install the appropriate licenses at a later time.
Setting Up the Network Environment to Use POAP
Modify the basic configuration script provided by Cisco or create your own script.
(Optional)Put the POAP configuration script and any other desired software image and switch configuration files on a USB device that is accessible to the switch.
Deploy a DHCP server and configure it with the interface, gateway, and TFTP server IP addresses and a bootfile with the path and name of the configuration script file. (This information is provided to the switch when it first boots.)
You do not need to deploy a DHCP server if all software image and switch configuration files are on the USB device.
Deploy a TFTP server to host the configuration script.
Deploy one or more servers to host the software images and configuration files.