External Connectivity

netlab contains several mechanisms that allow you to manage physical labs, add physical devices to virtual labs, connect to the outside world from virtual lab devices, or use network management software packaged as containers or virtual machines with your virtual labs.

Outbound Connectivity

libvirt and containerlab try to add IPv4 default routes to lab devices. libvirt uses a DHCP option, containerlab installs a default route into the container network namespace[1]. Most network devices running in a virtual lab are thus able to reach external destinations.

Most box-building recipes for libvirt Vagrant boxes recommend using a management VRF for the management interface. The default route is thus installed into the management VRF, and the client you’re using on the network device must be VRF-aware to reach external destinations. For example, you’ll have to use a command similar to ping vrf name destination to ping external IP addresses.

Connecting to Lab Devices

libvirt and containerlab providers create configuration files that connect all lab devices to a management network. Together with the default route configured on network devices, it’s always possible to reach the management IP address of every device in your lab, but you have to fix the routing in the external network – the management network IPv4 prefix has to be reachable from the external network.

Alternatively, use graphite for GUI-based SSH access to your lab network or port forwarding to map VM/container management TCP ports to the host ports. Port forwarding is always used with Virtualbox, and configurable with libvirt and containerlab providers. Use netlab report mgmt to display the host-to-lab-device TCP port mapping.

Finding the Management IP Addresses

The netlab report mgmt command displays the management IP addresses of the lab devices, protocol used to configure the devices (SSH, NETCONF, or Docker), and the username/password used by netlab to configure the device.

Alternatively, you could use Ansible inventory to find the same information:

• Run ansible-inventory --host _device-name_ to display the Ansible variables for the specified lab device.

• Look for ansible_host variable or ipv4 value in mgmt dictionary.

Finally, you could display node information in YAML format with the netlab inspect –node nodename command, or analyze the nodes dictionary in the netlab.snapshot.yml file with yq or a custom script.

Using SSH Port Forwarding

netlab can also create an SSH configuration file that you can add to your .ssh directory to access lab devices directly through SSH sessions using the netlab host as a proxy host[2].

After starting the lab, run netlab report ssh_config (more details) in the lab directory and save the contents into a file in your workstation’s .ssh directory. Use Include directive in the SSH config file[3] to give your ssh client access to the definitions of lab devices.

You might have to set several default parameters, either in the user default file or by using environment variables, to adapt the contents of the SSH configuration to your environment:

• defaults.ssh.hostname – The name under which the netlab server is known on your workstation (default: netlab). You have to set this parameter to a hostname that is resolvable on your workstation or combine it with the defaults.ssh.publicip parameter, in which case the SSH configuration file will include the definition of the hostname specified in this parameter[4].

• defaults.ssh.publicip – The public IP address you can use to reach the netlab server. Use this parameter if you’re running the netlab host in an environment where its public IP address might change (for example, in a public cloud).

• defaults.ssh.netlabpath – The netlab command path when it’s not in the default PATH[5].

The ssh_config report can also set up SSH port forwarding using the netlab_ssh_forward node variable. For example, using the following lab topology, you’d get access to the firewall’s HTTPS port (port 443) through the workstation (localhost) port 8080 after establishing an SSH session to the netlab host.

nodes:
  fw:
    netlab_ssh_forward:
    - 8080:443

Control-Plane Connectivity

If you need control-plane connectivity to your lab devices (for example, you’d like to run BGP with a device outside of your lab), consider running your additional devices as virtual machines in the lab. Please see Unknown Devices and Unprovisioned Devices for more details.

To connect libvirt virtual machines or containerlab containers to the outside world, set libvirt.uplink or clab.uplink link attribute on any link in your topology.

VirtualBox uses a different connectivity model. It maps device TCP/UDP ports into host TCP/UDP ports. The default ports mapped for each network device are ssh, http, and netconf. You can add further forwarded ports to the defaults.providers.virtualbox.forwarded parameter; the details are beyond the scope of this tutorial.

Unprovisioned Devices

The easiest way to add network management software (or any third-party workload) to your lab is to deploy it as a node in your network:

• Define an extra linux node in your lab topology

• Use the image node attribute to specify the node’s Vagrant box or container image.

The lab provisioning process will configure the static routes on your VM/container so that it can reach all other devices in your lab.

The VM device provisioning process will fail if your VM does not contain Python (used by Ansible) or the necessary Linux CLI commands (example: ip to add static routes); container interface addresses and routing tables are configured from the Linux server.

If you want to use a VM that cannot be configured as a Linux host, put that node into the unprovisioned group, for example:

---
defaults.device: iosv
  
nodes:
  r1:
  r2:
  nms:
    device: linux
    image: awesome-sw

groups:
  unprovisioned:
    members: [ nms ]

Warning

Devices in the unprovisioned group will not get IP addresses on interfaces other than the management interface, or static routes to the rest of the network.

As they are still connected to the management network, they can always reach the management interfaces of all network devices.

Unmanaged Devices

In advanced scenarios connecting your virtual lab with the outside world, you might want to add external devices to your lab topology without managing or provisioning them[6].

For example, if you want to have a BGP session with an external router:

• Define the external router as another device in your lab topology.

• Use static IP prefixes on the link between the virtual devices and the external router to ensure the virtual devices get IP addresses from the subnet configured on the external router

• Define BGP AS numbers used by your devices and the external router – netlab will automatically build IBGP/EBGP sessions between lab devices and the external device

• Use unmanaged node attribute on the external node to tell netlab not to include it in Ansible inventory or Vagrant/containerlab configuration files

Here is the resulting topology file using an Arista vEOS VM running BGP with an external Arista EOS switch. The lab is using libvirt public network to connect the VM to the outside world:

defaults.device: eos
module: [ bgp ]
nodes:
  vm:
    bgp.as: 65000
  sw:
    unmanaged: True
    bgp.as: 65001
links:
- vm:
    ipv4: 10.42.0.2/24
  sw:
    ipv4: 10.42.0.1/24
  libvirt.public: True

Tip

You still have to specify the device type (either in the node or as the default device type) for unmanaged nodes. netlab uses the device type to determine which features a node supports. If you want to use an unsupported unmanaged device, set ‌device to ‌none.

Managing Physical Devices

If you want to create configurations for a prewired physical lab, use the external provider.

Before using netlab with a physical lab, you must create a lab topology specifying the management IP addresses and interface names for all devices in your lab. Once that’s done, save the topology as a blueprint for further lab work.

Starting with the physical lab blueprint topology, add addressing plans (if needed), configuration modules, and configuration module parameters. Use netlab up to start the data transformation and configuration deployment on physical devices.

Please note that netlab does not contain a cleanup procedure for physical devices – you’ll have to remove the device configurations before starting the next lab.

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[1]

The default route added to the Linux kernel by containerlab might not be displayed by the network operating system. For example, if you execute show ip route on an Arista EOS container, you won’t see a default route, but you’ll still be able to reach external destinations.

[2]

If you’re not familiar with SSH configuration files, explore LocalForward, ProxyJump, ProxyCommand, and RemoteCommand OpenSSH configuration parameters.

[3]

At the beginning of the file

[4]

Sounds confusing? Try it out; you cannot do any damage until you save the report results in a file.

[5]

The SSH process doing proxying on the netlab server is started without executing the shell login script

[6]

Assuming you connected one or more Linux bridges in your lab with the outside world.