Linux networking

Network interfaces

ifconfig → Display network interfaces

ifconfig eth0 192.168.2.1 netmask 255.255.255.0 up → Create an interface and bring it up

ifup eth0 → Bring interface up

ifdown eth0 → Bring interface down

ip link show → Show interface information for all interfaces

ip -s link show eth0 → Show the statistics of an interface

ip address show → Show ip addresses allocated to interfaces

ip link set eth0 up → Bring interface up

ip link set eth0 down → Bring interface down

ip address add 192.168.1.1/24 dev eth0 → Add an ip address to an interface

Route

sudo route add -net 192.168.2.1/23 gw 10.11.12.3 → Add a new route

sudo route del -net 192.168.2.1/23 → Delete a route

ip route add 192.168.2.1/23 via 10.11.12.3 → Add route with ip command

ip route delete 192.168.2.1/23 → Delete route with ip command

dhclient

sudo dhclient → Obtain a fresh ip

arp

arp → View arp cache

ip neighbour show → View arp cache with ip command

Troubleshooting

ping -c 3 [www.google.com](<http://www.google.com>) → Test whether or not a packet can reach a host and stop sending echo request packets after the count (3) has been reached

traceroute [google.com](<http://google.com>) → See how packets are getting routed

sudo tcpdump -i wlan0 → Capture packet data on an interface

netstat -anpt → Find out what services are listening for connection on the machine

sudo service network-manager restart → Restart the network manager

rfkill list → List wifi to see if its blocked or not

rfkill block 0 → Block wifi interface

rfkill unblock 0 → Unblock wifi interface

DNS

nslookup [www.google.com](<http://www.google.com>) → Query name servers to find information about resource records

dig [www.google.com](<http://www.google.com>) → Getting information about DNS name servers