Persistent Configuration

Sometimes it is desirable to have the network configuration persist across reboots. This section describes how to achieve that using systemd.

Table of Contents

1. Prerequisites
2. Configuration
   1. Port Splitting
      1. Using udev
   2. Network Configuration
   3. Required changes to MACAddressPolicy
3. Further Resources

Prerequisites

This section assumes systemd is used as the service manager on the system and that NetworkManager is disabled. To disable NetworkManger, which is mainly aimed at desktop environments, run:

$ systemctl disable NetworkManager

In addition, systemd-networkd needs to be enabled:

$ systemctl enable systemd-networkd

To prevent systemd from waiting until all the links are configured, edit the following file as specified below:

# /usr/lib/systemd/system/systemd-networkd-wait-online.service
...
ExecStart=/usr/lib/systemd/systemd-networkd-wait-online -i <mgmt>
...

Where <mgmt> is replaced with the name of the management interface (e.g., enp0s20f0). This will make systemd only wait for the management interface to be configured and gain carrier.

Configuration

Port Splitting

To split a port during system initialization and have the configuration persist across reboots, it is possible to use a systemd service unit file.

# /etc/systemd/system/[email protected]
[Unit]
Description=Split port sw1p%i by 4
Documentation=man:devlink-port(8)
After=network.target

[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/usr/sbin/devlink port split sw1p%i count 4
ExecStop=/usr/sbin/devlink port unsplit sw1p%is0

[Install]
WantedBy=multi-user.target

The above service will split port sw1p12 by 4 when executed:

$ systemctl start split-port@12

And unsplit the port when stopped:

$ systemctl stop split-port@12

To have the port split during system initialization, enable the port-split service:

$ systemctl enable split-port@12

Using udev

The previously described method will not automatically split the port in case the driver is removed and then loaded again.

It is possible to automatically split the port when it appears using udev:

# /etc/udev/rules.d/10-local.rules
SUBSYSTEM=="net", ACTION=="add", ATTR{phys_switch_id}=="<phys_switch_id>", \
	ATTR{phys_port_name}=="p12", ENV{SYSTEMD_WANTS}="[email protected]"

# /etc/systemd/system/[email protected]
[Unit]
Description=Split port sw1p%i by 4
Documentation=man:devlink-port(8)

[Service]
Type=simple
ExecStart=/usr/sbin/devlink port split sw1p%i count 4

Network Configuration

systemd can configure many aspects of the network. To see the full list of possible configuration options please refer to the Further Resources section.

The example below shows how to create a VLAN-aware bridge between two switch ports.

# /etc/systemd/network/25-bridge.netdev
[NetDev]
Description=Simple VLAN-aware bridge
Name=br0
Kind=bridge

[Bridge]
DefaultPVID=1
VLANFiltering=true

# /etc/systemd/network/25-bridge.network
[Match]
Name=br0

[Network]
Address=192.0.2.1/24

# /etc/systemd/network/25-bridge-slave-1.network
[Match]
Name=sw1p1

[Network]
Bridge=br0

# /etc/systemd/network/25-bridge-slave-2.network
[Match]
Name=sw1p3

[Network]
Bridge=br0

To make the changes take effect, start the systemd-networkd service:

$ systemctl start systemd-networkd

Assuming the service is enabled, the configuration will persist across reboots.

Required changes to MACAddressPolicy

Since systemd version 242, systemd will set a persistent MAC address on virtual interfaces such as bridges. Therefore, upon the enslavement of an interface to the bridge, the bridge will no longer inherit the interface's MAC address.

The driver requires that all the router interfaces share the same MSBs in their MAC. It will therefore veto the addition of an IP address on the bridge interface with the following error:

Error: mlxsw_spectrum: All router interface MAC addresses must have the same prefix.

To prevent systemd from changing the MAC address of interfaces, MACAddressPolicy needs to be set to none.

# /etc/systemd/network/10-ignore.link
[Match]
OriginalName=*

[Link]
MACAddressPolicy=none

Further Resources

1. man systemd-networkd
2. man systemd.network
3. man systemd.netdev