linuxexpert-practice-labs/labs/linux-plus/1-4-1-network-configuration

Linux+ 1.4.1: Network configuration

How names are resolved, and a second address on an interface: with NetworkManager on the RHEL family, with a Netplan file on Ubuntu.

Before you start

So that you never touch the interface you're connected over, the lab adds a practice interface, lab0 (a dummy device, with nothing on the other end). On the RHEL family it's NetworkManager connection lab0, with the address 192.168.76.1/24. On Ubuntu, systemd-networkd creates it with no address. It comes back at every boot. Use lab0 wherever the chapter uses your main connection or interface.

Tasks

1. Make the name labtest resolve to 10.99.99.99 without DNS. Check it with getent hosts labtest, and see that dig +short labtest (which only asks DNS) doesn't find it. Leave the line in place until you've run le-lab check.
2. RHEL family: add a second address, 192.168.77.10/24, to connection lab0, keeping the first, and bring the connection up again.
3. Ubuntu: give lab0 the address 192.168.77.10/24 with a new Netplan file, /etc/netplan/90-lab.yaml, readable only by root, and apply it with netplan try.

When le-lab check passes, take the line and the address out again as the chapter shows, or leave it to le-lab reset.

Hints

• /etc/resolv.conf, the hosts: line in /etc/nsswitch.conf, /etc/hosts. On the RHEL family, dig is in bind-utils.
• nmcli -t -f NAME,DEVICE con show --active, nmcli con mod NAME +ipv4.addresses ..., nmcli con up NAME, ip -br addr.
• An ethernets: entry for lab0 with addresses: [...]; chmod 600; netplan try (press Enter to keep it), netplan status.