QEMU based Nexus / NX-OS simulation approach

Summary

A QEMU based approach that shows how to boot a QEMU NX-OS VM image as it can be downloaded from Cisco and initializes the networking of the NX-OS device.

A full article discussing this topic can be read here.

Background

The setup serves as a demonstration how to set up test devices in an automated way for developing network applications.

Preconditions

You need to have the following Debian packages installed:

qemu-system-x86
qemu-utils
ovmf
expect

You need to download and store your QCOW2 NX-OS image in a location that needs to be specified by the SOURCE_IMAGE environment variable in qemu-snapshot-and-start.sh.

Components

There are the following components:

qemu-snapshot-and-start.sh: The script that creates a new snapshot from an image, and spawns a new QEMU from it.
qemu-start-from-snapshot.sh: The script that spawns a new QEMU with a pre-existing image.
expect.ex: An expect script that fights through the NX-OS configuration until a initial user/password is set and the management interface has a working network via QEMUs DHCP.

Status

The QEMU launcher is creating a snapshot first so we don't alter the original image file. The QEMU launcher will stop in the QEMU command prompt ('(qemu)') which might be confusing, but this is ok. The QEMU monitor commands are listed here.

The expect script is working to set up management interface via DHCP. The expect script does:

Setup admin user 'admin' with password 'admin'.
Setup login user 'vagrant' with password 'vagrant'.
Setup console port 2023 (usable via telnet).
Setup port binding to TCP port 3022 on host towards TCP port 22 on guest (usable via SSH).
Copies the running-config to the startup-config to save user and network configs.

How to use

Define the image location in $SOURCE_IMAGE, then start the qemu-snapshot-and-start.sh in the first shell, so QEMU can boot up.

Start expect.ex right away in a second shell so the starting VM will be configured.

The management interface of the simulated device will be available via SSH:

$  ssh -oPubKeyAuthentication=false -p3022 admin@localhost
The authenticity of host '[localhost]:3022 ([127.0.0.1]:3022)' can't be established.
RSA key fingerprint is SHA256:FronHu+9JxcRpCOvGcwpKEF+MZdfWoS94cM6MhcGghg.
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Warning: Permanently added '[localhost]:3022' (RSA) to the list of known hosts.
User Access Verification
Password: 

Bad terminal type: "xterm-256color". Will assume vt100.
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