Managing Network Connections on Linux

Configure Network Features

need to configure 5 things to interact on a network:
- host address
- network subnet address
- default router (aka gateway)
- system host name
- Domain Name System (DNS) server address
3 ways to configure this information:
- manually editing network configuration files
- using GUI tool
- using command-line tools

The Network Manager tool is a common program on many Linux distributions to provide a GUI for defining network connections.

starts automatically at boot time
appears in system tray
- wired connection shows a mini network with blocks icon
- wireless connection shows an empty radio signal
  - click the icon to connect to your wireless access point
- click icon > Edit Connections to edit network connection settings
In the Network Connections window, can select a connection then click edit to edit its information

domain mydomain.com
search mytest.com
nameserver 192.168.1.1

domain entry defines the domain name assigned to the network
- system appends this domain name to any host names you specify, by default
search entry defines any additional domains used to search for host names
nameserver entry defines DNS server assigned to your network
- can have multiple DNS servers
- just add multiple nameserver entries
this file may reset at reboot
/etc/hosts can be used to manually enter connections to hosts
- /etc/nsswitch.conf file defines whether the Linux system checks this file before or after using DNS to look up the host name

Network Manager has 2 CLI tools:
- nmtui provides a simple text-based menu tool
  - displays a stripped-down version of the GUI tool
- nmcli provides a text-only command-line tool
  - displays current network devices and their settings, by default
both help guide through setting up the required network information

ethtool displays Ethernet settings for a network interface
- by default, displays current configuration settings
- can change speed, duplex, and auto negotiation
ifconfig displays or sets the IP address and netmask values for a network interface
- legacy command
ip displays or sets the IP address, netmask, and router values for a network interface
- e.g., ip address show
- set host address and netmask for an interface:
  - ip address add 10.0.2.15/24 dev enp0s3
- set default router for an interface
  - ip route add default via 192.168.1.254 dev enp0s3
- make an interface active
  - ip link set enp0s3 up
- before assigning an address to a wireless interface, must first use the iwconfig command
iwconfig displays or sets the SSID and encryption key for a wireless interface
- assign a wireless SSID and encryption key:
  - iwconfig wlan0 essid "My Network" key s:mypassword
iwlist displays all wireless signals your wireless card detects
- e.g., iwlist wlan0 scan
route displays or sets the default router address
- e.g., route add default gw 192.168.1.254
common DHCP client programs for Linux:
- dhcpcd
  - most popular
- dhclient
- pump

can test host name with host command
- e.g., host www.linux.org
- queries the DNS server to determine the IP addresses assigned to the specified host name
- returns all IP addresses associated with host name by default
- can specify IP address to find the associated host name
  - host 107.170.40.56
dig command displays all DNS data records associated with a specific host or network
- e.g., dig www.linux.org
  - dig linux.org MX
nslookup displays DNS information for multiple servers or domains
- can run in interactive mode