Networking

Most Linux systems are connected to a network as a client system, or to provide services to other systems. Knowing how to configure, monitor, and audit the network configuration is more than useful. In this section we look at the available options.

Network configuration

The system itself can’t talk with other systems if it doesn’t have any protocol to communicate. Nowadays that is mostly IP . The local configuration for the network is usually stored in /etc/network or in a network manager in /etc.

Common components that help with managing the network configuration, include:

Netplan
networkd
NetworkManager

Good to know: Netplan uses a backend like networkd or NetworkManager to apply the configuration.

IP address information

To retrieve existing network information and IP in particular, we use the ip command. As this command has several subcommands, we use address in this particular case.

ip address

This output might include:

Link name
Status
MTU size
MAC address
Any alternative name (alias)
IP address and netmask
IPv6 information

Gateway or router

To connect to systems outside the network, we use a gateway. This is a (virtual) router to move network packets between different networks. To see routing information, we can use the route subcommand.

ip route

DNS servers

To translate between host names and IP addresses, we use DNS . The servers to be used are typically configured within the network manager. In some cases they are defined directly in /etc/resolv.conf. In the past, this was the common way to do this, but that is changing. Still, it is good to check the configuration and see what is defined.

cat /etc/resolv.conf

When using systemd, you might even see the DNS server pointhing to a local address like 127.0.0.53, meaning it uses a local service.

resolvectl status