Network

Interfaces & IP Addresses

ip is the modern tool for everything interface-related; ifconfig is its deprecated predecessor. a is short for addr.

$ ip a

$ ip link show

$ nmcli device status

$ ifconfig -a

Identify the network hardware behind the interfaces.

$ lspci | grep -i 'network\|ethernet'

$ lshw -class network

$ ethtool eth0

Configuring Interfaces

Bring interfaces up or down and assign addresses manually (root required). Changes made with ip are gone after a reboot; make them permanent in your network manager.

$ ip link set eth0 up

$ ip link set eth0 down

$ ip addr add 192.168.1.50/24 dev eth0

Release the DHCP lease and request a new one.

$ dhclient -r eth0

$ dhclient eth0

Wi-Fi

With NetworkManager, nmcli scans, connects, and even reveals the password of the current network.

$ nmcli device wifi list

$ nmcli device wifi connect [SSID] password [password]

$ nmcli device wifi show-password

Stored Wi-Fi passwords live in NetworkManager's connection files (root required).

$ sudo grep -r "psk=" /etc/NetworkManager/system-connections/

On systems using iwd instead of NetworkManager, use iwctl.

$ iwctl station wlan0 get-networks

$ iwctl station wlan0 connect [SSID]

External IP

Your public address as seen from the internet, via HTTP or DNS.

$ curl ifconfig.me

$ dig +short myip.opendns.com @resolver1.opendns.com

Testing Connectivity

ping checks if a host answers, traceroute shows the path packets take, and mtr combines both in a live view.

$ ping [host]

$ ping -c 4 [host]

$ traceroute [host]

$ tracepath [host]

$ mtr [host]

Check whether a specific TCP port is reachable.

$ nc -zv [host] [port]

$ telnet [host] [port]

Measure raw throughput between two machines (run iperf3 -s on one, -c on the other).

$ iperf3 -s

$ iperf3 -c [serverIp]

DNS Lookups

Resolve names to addresses and back. dig +short prints just the answer; -x does a reverse lookup of an IP.

$ dig [domain]

$ dig +short [domain]

$ dig -x [ip]

$ dig MX [domain]

$ host [domain]

$ nslookup [domain]

$ resolvectl query [domain]

Look up who owns a domain or IP range.

$ whois [domain]

Downloading Files

wget downloads and resumes, curl -O saves under the remote name (-L follows redirects), aria2c and axel split downloads over parallel connections.

$ wget [url]

$ wget -c [url]

$ curl -LO [url]

$ aria2c [url]

$ axel [url]