Running Multiple Labs on Linux Servers

Using the default settings, netlab cannot run more than a single lab instance on a Linux server as it relies on the default network names and IP prefixes used by the vagrant-libvirt plugin and containerlab orchestration system.

The multilab plugin modifies virtualization defaults for every lab instance, allowing you to run multiple libvirt- or container-based labs in parallel. Using its default settings, the plugin modifies:

  • Lab name that is used as a prefix for VM-, container, and bridge names.

  • Name of the management network and underlying Linux bridge

  • IP prefix of the management network.

The plugin has been tested with libvirt and clab netlab virtualization providers.


  • While you can use the same topology file for multiple lab instances, you MUST run each lab instance in a different working directory.

  • The ‌multilab plugin changes the lab topology parameters ‌after the topology file, user- and system defaults have been processed. You cannot change a parameter controlled by the ‌multilab plugin with a topology file setting; you must change the corresponding defaults.multilab.change parameter. See also Behind the Scenes

Using the Plugin

You can use multilab plugin in three scenarios:

Static instances: You want to run different lab topologies in parallel but not multiple instances of the same lab. Specify in the lab topology and add the multilab plugin with the lab topology plugin parameter.

# Lab topology using the multilab plugin
plugin: [ multilab ]
provider: libvirt 12

Per-user instances: You have multiple users using the same Linux servers. Each user is allowed to run one lab at a time. Specify in the user defaults file and activate the multilab plugin with the plugin parameter in the same file.

# User defaults file activating multilab plugin
plugin: [ multilab ] 12


Use the system-wide netlab status file if multiple users start lab instances on the same Linux server. You can change the location of the status file with the ‌defaults.lab_status_file parameter.

All netlab users should be able to write to the netlab status file and the parent directory.

Dynamic labs: Users can run multiple lab instances, including several instances of the same lab topology. Each instance still needs a unique multilab ID that has to be allocated by an external system that passes to netlab.


Each lab instance must be started in a different working directory. However, you can use the same lab topology file.

You can use the -s argument of netlab create or netlab up command to set Use the --plugin multilab CLI argument when specifying the multilab ID with the -s argument.

# Start the lab with the multilab plugin
netlab up --plugin multilab -s topology.yml

You can also use the netlab environment variables to specify the default plugin(s) to use and the multilab ID. For example:

$ export NETLAB_PLUGIN=multilab

Behind the Scenes

multilab plugin uses lab id specified in to change system defaults or topology parameters listed in defaults.multilab.change dictionary. The default parameters multilab plugin changes are specified in the netsim/defaults/multilab.yml file; you can add your parameters if needed.

  name: 'ml_{id}' 'ml_{id}'
  defaults.providers.libvirt.tunnel_id: '{id}'
  defaults.providers.libvirt.vifprefix: 'vif_{id}'
    ipv4: '192.168.{id}.0/24'
    _network: 'nl_mgmt_{id}'
    _bridge:  'nl_mgmt_{id}'

String values specified in the defaults.multilab.change dictionary are evaluated as f-formatted Python strings. You can use the id variable (the value of parameter) or any lab topology parameter (including system defaults) in the evaluated expressions.

Interface Name Limitations

The plugin modifies how netlab creates Linux bridge and interface names. The maximum length of a Linux interface name is 15 characters, limiting the size of the prefix taken from the topology name parameter to form interface/bridge names:

  • The bridge name of the management network cannot be longer than 15 characters.

  • Linux bridge names used for multi-access links are created from the first ten characters of the name parameter followed by the linkindex value.

  • The names of container interfaces connected to Linux bridges are created from the first six characters of the name parameter followed by node id and interface ifindex.

  • The names of libvirt interfaces connected to Linux bridges are composed of vifprefix, node name and interface ifindex. As the interface names cannot be longer than 15 characters, the libvirt interface name is not set if the resulting string is longer than that (libvirt will use an internally-generated interface name).


The first six characters of the lab topology name generated from the multilab change dictionary must be unique. Otherwise, netlab generates duplicate container interface names in failed containerlab deployments. In a libvirt-only environment, the first ten characters of the lab topology name must be unique.