Networking service

The open-source project systemd-networkd is widely available in modern Linux distributions. The project uses a declarative configuration language that's similar to the rest of the systemd framework. Its primary configuration file types are .network and .link files.

The amazon-ec2-net-utils package generates interface-specific configurations in the /run/systemd/network directory. These configurations enable both IPv4 and IPv6 networking on interfaces when they're attached to an instance. These configurations also install policy routing rules that help ensure that locally sourced traffic is routed to the network through the corresponding instance's network interface. These rules ensure that the right traffic is routed through the Elastic Network Interface (ENI) from the associated addresses or prefixes. For more information about using ENI, see Using ENI in the Amazon EC2 User Guide for Linux Instances.

You can customize this networking behavior by placing a custom configuration file in the /etc/systemd/network directory to override the default configuration settings contained in /run/systemd/network.

The systemd.network documentation describes how the systemd-networkd service determines the configuration that applies to a specific interface. It also generates alternative names, known as altnames, for the ENI-backed interfaces to reflect the properties of various Amazon resources. These ENI-backed interface properties are the ENI ID and the DeviceIndex field of the ENI attachment. You can refer to these interfaces using their properties when using various tools, such as the ip command.

AL2023 instance interface names are generated using the systemd slot naming scheme. For more information, see systemd.net naming scheme.

Additionally, AL2023 uses the fq_codel active queue management network transmission scheduling algorithm by default. For more information, see CoDel overview.