Exercise: Configure a static connection

Build a static network configuration from scratch on a virtual interface: create it, check that it works, extend it, change it, and see that it survives a reboot. Your real network connection is never touched.

Configure a static connection

Create a static dummy connection with nmcli.
Add and replace addresses, applying them with connection up.
Verify persistence across a reboot and clean up.

Start the exercise

On workstation, start the exercise. It removes a dummy0 connection left by an earlier run from servera.

[student@workstation ~]$ lab start sa-nmcli

Later tasks assume that you are logged in to the server they name: ssh student@servera from workstation, then sudo -i for a root shell.

Look before you touch

On servera as root (sudo -i), list the devices and the connections.

[student@workstation ~]$ ssh student@servera
[student@servera ~]$ sudo -i
[root@servera ~]# nmcli device status
DEVICE  TYPE      STATE                   CONNECTION
enp5s0  ethernet  connected               System enp5s0
lo      loopback  connected (externally)  lo
[root@servera ~]# nmcli connection show
NAME           UUID                                  TYPE      DEVICE
System enp5s0  9310e179-14b6-430a-6843-6491c047d532  ethernet  enp5s0
lo             f70215b4-09f6-4aeb-b431-8be72ac28cce  loopback  lo

Create dummy0

Create a connection named dummy0 for the device dummy0, with the static address 10.20.30.1/24 and IPv6 disabled. Check the address with ip.

[root@servera ~]# nmcli connection add type dummy ifname dummy0 con-name dummy0 ipv4.method manual ipv4.addresses 10.20.30.1/24 ipv6.method disabled
Connection 'dummy0' (1eb3d901-8d60-465a-98fb-d365ea4b7649) successfully added.
[root@servera ~]# ip -br addr show dummy0
dummy0           UNKNOWN        10.20.30.1/24

A dummy device shows state UNKNOWN because it has no cable to sense. That is normal.

Test the address

Ping your own new address once. Which route handles it?

[root@servera ~]# ping -c 1 10.20.30.1 | head -2
PING 10.20.30.1 (10.20.30.1) 56(84) bytes of data.
64 bytes from 10.20.30.1: icmp_seq=1 ttl=64 time=0.104 ms
[root@servera ~]# ip route | grep 10.20.30
10.20.30.0/24 dev dummy0 proto kernel scope link src 10.20.30.1 metric 550

The kernel added the connected route for 10.20.30.0/24 automatically.

Add a second address

Add 10.20.30.2/24 to the profile. Check ip addr before and after applying the change. Why do they differ?

[root@servera ~]# nmcli connection modify dummy0 +ipv4.addresses 10.20.30.2/24
[root@servera ~]# ip -br addr show dummy0
dummy0           UNKNOWN        10.20.30.1/24
[root@servera ~]# nmcli connection up dummy0
Connection successfully activated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/4)
[root@servera ~]# ip -br addr show dummy0
dummy0           UNKNOWN        10.20.30.1/24 10.20.30.2/24

modify only edited the saved profile. up applied it to the device.

Replace the addresses, add a gateway and DNS

Replace the whole list with one address, 10.20.30.9/24, and add a DNS server 10.20.30.53 and a gateway 10.20.30.254 to the profile. Apply it. What changes in the routing table and in /etc/resolv.conf?

[root@servera ~]# nmcli connection modify dummy0 ipv4.addresses 10.20.30.9/24 ipv4.dns 10.20.30.53 ipv4.gateway 10.20.30.254
[root@servera ~]# nmcli connection up dummy0 > /dev/null
[root@servera ~]# ip -br addr show dummy0
dummy0           UNKNOWN        10.20.30.9/24
[root@servera ~]# ip route
default via 172.25.250.254 dev enp5s0 proto dhcp src 172.25.250.10 metric 100
default via 10.20.30.254 dev dummy0 proto static metric 550
10.20.30.0/24 dev dummy0 proto kernel scope link src 10.20.30.9 metric 550
172.25.250.0/24 dev enp5s0 proto kernel scope link src 172.25.250.10 metric 100
[root@servera ~]# cat /etc/resolv.conf
# Generated by NetworkManager
search lab.example.com
nameserver 172.25.250.254
nameserver 10.20.30.53

Without the +, the address list was replaced. There are now two default routes; the one with the lower metric (100, on enp5s0) is used, so the dummy gateway does not take over. The DNS server was appended to resolv.conf, after the existing one.

See the file, reboot, and check

Show the profile file. Reboot, log in again, and check that dummy0 came back with its address.

[root@servera ~]# cat /etc/NetworkManager/system-connections/dummy0.nmconnection
[connection]
id=dummy0
uuid=1eb3d901-8d60-465a-98fb-d365ea4b7649
type=dummy
interface-name=dummy0
...output omitted...
[ipv4]
address1=10.20.30.9/24
dns=10.20.30.53;
gateway=10.20.30.254
method=manual
...output omitted...
[root@servera ~]# systemctl reboot
[student@workstation ~]$ ssh student@servera
[student@servera ~]$ ip -br addr show dummy0
dummy0           UNKNOWN        10.20.30.9/24

The address came back because it is in a profile. (ip addr add alone would have vanished.)

Delete it

[student@servera ~]$ sudo nmcli connection delete dummy0
Connection 'dummy0' (1eb3d901-8d60-465a-98fb-d365ea4b7649) successfully deleted.
[student@servera ~]$ sleep 3; ip -br addr
lo               UNKNOWN        127.0.0.1/8 ::1/128
enp5s0           UP             172.25.250.10/24 fe80::216:3eff:fe88:153c/64
[student@servera ~]$ cat /etc/resolv.conf | tail -1
nameserver 172.25.250.254
[student@servera ~]$ exit

The virtual device and the extra DNS server disappear a moment after the profile is deleted.

Grade and finish

Check your work with lab grade sa-nmcli, then put the exercise away with lab finish sa-nmcli.