RHCSA Rapid Track

Objectives

After completing this section, students should be able to manage network settings and devices with nmcli and NetworkManager.

NetworkManager

NetworkManager is a daemon that monitors and manages network settings. In addition to the daemon, there is a GNOME Notification Area applet that provides network status information. Command-line and graphical tools talk to NetworkManager and save configuration files in the /etc/sysconfig/network-scripts directory.

A device is a network interface. A connection is a configuration used for a device which is made up of a collection of settings. Multiple connections may exist for a device, but only one may be active at a time. For example, a system may normally be connected to a network with settings provided by DHCP. Occasionally, that system needs to be connected to a lab or data center network, which only uses static networking. Instead of changing the configuration manually, each configuration can be stored as a separate connection.

Viewing network information with nmcli

To display a list of all connections, use nmcli con show. To list only the active connections, add the --active option.

[root@desktopX ~]# nmcli con show
NAME            UUID                                  TYPE             DEVICE  
static-eth0  f3e8dd32-3c9d-48f6-9066-551e5b6e612d  802-3-ethernet   eth0   
System eth0  5fb06bd0-0bb0-7ffb-45f1-d6edd65f3e03  802-3-ethernet   -- 
guest        f601ca8a-6647-4188-a431-dab48cc63bf4  802-11-wireless  wlp3s0  
[root@desktopX ~]# nmcli con show --active
NAME            UUID                                  TYPE             DEVICE  
static-eth0  f3e8dd32-3c9d-48f6-9066-551e5b6e612d  802-3-ethernet   eth0   
guest        f601ca8a-6647-4188-a431-dab48cc63bf4  802-11-wireless  wlp3s0  

Specify a connection ID (name) to see the details of that connection. The lowercase settings represent the configuration of the connection. Setting and property names are defined in the nm-settings(5) man page. The uppercase settings are active data.

[root@desktopX ~]# nmcli con show "static-eth0"
...
ipv4.method:                            manual
ipv4.dns:                               172.25.254.254, 8.8.8.8
ipv4.dns-search:                        
ipv4.addresses:                         { ip = 172.25.X.10/24, gw = 172.25.X.254 }
ipv4.routes:                            
ipv4.ignore-auto-routes:                no
ipv4.ignore-auto-dns:                   no
ipv4.dhcp-client-id:                    --
ipv4.dhcp-send-hostname:                yes
ipv4.dhcp-hostname:                     --
ipv4.never-default:                     no
ipv4.may-fail:                          yes
ipv6.method:                            auto
...

The nmcli command can also be used to show device status and details.

[root@desktopX ~]# nmcli dev status
DEVICE  TYPE      STATE      CONNECTION  
eth0    ethernet  connected  static-eth0 
wlp3s0  wifi      connected  guest    
lo      loopback  unmanaged  --          
[root@desktopX ~]# nmcli dev show eth0
GENERAL.DEVICE:                         eth0
GENERAL.TYPE:                           ethernet
GENERAL.HWADDR:                         52:54:00:00:00:0A
GENERAL.MTU:                            1500
GENERAL.STATE:                          100 (connected)
GENERAL.CONNECTION:                     static-eth0
GENERAL.CON-PATH:                       /org/freedesktop/NetworkManager/ActiveConnection/1
WIRED-PROPERTIES.CARRIER:               on
IP4.ADDRESS[1]:                         ip = 172.25.X.10/24, gw = 172.25.X.254
IP4.DNS[1]:                             172.25.254.254
IP6.ADDRESS[1]:                         ip = fe80::5054:ff:fe00:b/64, gw = ::

Creating network connections with nmcli

When creating a new connection with nmcli, the order of the arguments is important. The common arguments appear first and must include the type and interface. Next, specify any type-specific arguments and finally specify the IP address, prefix, and gateway information. Multiple IP addresses may be specified for a single device. Additional settings such as a DNS server are set as modifications once the connection exists.

Examples of creating new connections

Follow along with the next steps while your instructor discusses nmcli syntax.

Type options

Type options depend on the type used. An ethernet-type connection may optionally specify a MAC address for the connection. A wifi-type connection must specify the SSID and may specify additional options. Many other types are available, including bridge, bond, team, VPN, and VLAN. To view all the options, use nmcli con add help.

[root@desktopX ~]# nmcli con add help 
Usage: nmcli connection add { ARGUMENTS | help }

ARGUMENTS := COMMON_OPTIONS TYPE_SPECIFIC_OPTIONS IP_OPTIONS

  COMMON_OPTIONS:
                  type <type>
                  ifname <interface name> | "*"
                  [con-name <connection name>
                  [autoconnect yes|no]

                  [save yes|no]

  TYPE_SPECIFIC_OPTIONS:
    ethernet:     [mac <MAC address>
                  [cloned-mac <cloned MAC address>
                  [mtu <MTU>
...

Modifying network interfaces with nmcli

An existing connection may be modified with nmcli con mod arguments. The arguments are sets of key/value pairs. The key includes a setting name and a property name. Use nmcli con show "<ID>" to see a list of current values for a connection. The nm-settings(5) man page documents the setting and property names and usage.

[root@desktopX ~]# nmcli con show "static"
connection.id:                          static
connection.uuid:                        f3e8dd32-3c9d-48f6-9066-551e5b6e612d
connection.interface-name:              eth0
connection.type:                        802-3-ethernet
connection.autoconnect:                 yes
connection.timestamp:                   1394905322
connection.read-only:                   no
...

Examples of connection modifications

Follow along with the next steps while your instructor discusses nmcli syntax.

[root@desktopX ~]# nmcli con up "static"

Summary of nmcli commands

Basic device and connection commands for nmcli: