How to Configure systemd-networkd for Network Teaming and Bridging in Ubuntu

In high-availability enterprise servers and virtualization hosts running KVM or LXC containers, network interfaces must deliver redundant failover and shared Layer 2 connectivity. While traditional desktop Ubuntu systems use NetworkManager, modern server installations rely on systemd-networkd. Providing lightweight daemon performance and deep systemd integration, systemd-networkd enables administrators to construct hardware link aggregations (LACP 802.3ad bonding) and virtual switch bridges using declarative configuration files.

Understanding Virtual Network Devices: NetDev vs Network Files

systemd-networkd separates device definition from IP assignment using two file types located in /etc/systemd/network/:

• .netdev files: Define virtual network devices (such as bonds, VLANs, and software bridges) and specify kernel-level parameters like hashing algorithms and bridge forwarding delays.
• .network files: Match physical or virtual interfaces and apply Layer 3 configurations, including static IP addresses, DHCP parameters, routing tables, and master enslavement rules.

Enabling and Transitioning to systemd-networkd

Ensure systemd-networkd is enabled and operational:

sudo systemctl enable --now systemd-networkd
sudo systemctl enable --now systemd-resolved

Inspect active network interfaces using networkctl:

networkctl status

The command lists all network links along with their operational states (such as routable, carrier, or unmanaged).

Creating a High-Throughput 802.3ad Network Bond

Network bonding combines multiple physical NICs (e.g., eth0 and eth1) into a single virtual pipe. Assume we want an active-backup or LACP 802.3ad trunk.

Create the virtual bond netdev definition:

sudo nano /etc/systemd/network/10-bond0.netdev

Add the following configuration specifying 802.3ad dynamic link aggregation with Layer 3+4 hash balancing:

[NetDev]
Name=bond0
Kind=bond

[Bond]
Mode=802.3ad
TransmitHashPolicy=layer3+4
MIIMonitorSec=100ms
LACPTransmitRate=fast

Enslave the physical interfaces to the bond:

sudo nano /etc/systemd/network/20-bond-slave.network

[Match]
Name=eth0 eth1

[Network]
Bond=bond0

Creating a Virtual Software Bridge for Hypervisors and Containers

To enable virtual machines and containers to share the physical bond directly on the local subnet, construct a software bridge (br0):

Create the bridge netdev definition:

sudo nano /etc/systemd/network/30-br0.netdev

[NetDev]
Name=br0
Kind=bridge

[Bridge]
DefaultPVID=none
STP=yes

Attach the bond0 aggregated interface as a member of br0:

sudo nano /etc/systemd/network/40-bond-to-bridge.network

[Match]
Name=bond0

[Network]
Bridge=br0

Assigning Static IP Addressing to the Bridge Interface

Because the physical interfaces and the bond are enslaved to the bridge, assign the server’s static IP address directly to br0:

sudo nano /etc/systemd/network/50-br0.network

[Match]
Name=br0

[Network]
Address=192.168.1.50/24
Gateway=192.168.1.1
DNS=1.1.1.1 9.9.9.9

Applying Configuration and Validating Links

Reload and restart systemd-networkd to apply the new network hierarchy:

sudo networkctl reload
sudo systemctl restart systemd-networkd

Validate the operational status of all links:

networkctl list

Confirm that eth0 and eth1 display master bond0, that bond0 displays master br0, and that br0 reports status routable with your assigned static IP address.