Creating an External Bridge

Often carthage is used to create a layout of related machines that eventually need to connect to a broader network. Two mechanisms are used:

• The default networking provided by OCI Containers <carthage.oci.OciContainer and implementations such as Podman.

  • An :data:external network <carthage.network.external_network_key` that creates a bridge The assumption is any carthage.Machine placed on this network will be able to DHCP for an address.

    This tutorial focuses on the external network. By default, Carthage models the external network as a bridge whose name is given by the external_bridge_name config key.

    So, for example if /etc/carthage_system.conf (the default system configuration file) contains:

external_bridge_name: blaptop

Then Carthage will assume the existence of a bridge called blaptop that serves dhcp to any machine connected to it.

Creating the Bridge Device

To create a bridge device called blaptop, create a file /etc/systemd/network/blaptop.netdev with the following contents:

[NetDev]
Name=blaptop
Kind=bridge
[Bridge]
VLANFiltering=False

Configuring the Bridge

To provide networking for the bridge, create a file /etc/systemd/network/blaptop.network with the following contents:

[Match]
Name=blaptop
[Network]

Address=10.38.0.1/24
IPMasquerade=yes
DHCPServer=yes

Then run systemctl restart systemd-networkd to create and configure the bridge.

Configuring Carthage

In general attaching to a bridge requires root. Configuring qemu or other Machine implementations to allow using a bridge as non-root is beyond this tutorial.

To configure Carthage running as root to use blaptop, create or edit /etc/carthage_system.conf. This is a YAML file. Include the following key:

external_bridge_name: blaptop