Configuring the Network in Linux

Consider setting up the network in Linux Ubuntu.
View information about network interfaces:

ifconfig
ifconfig -a
ip -s -s link show

Example of enabling interfaces:

sudo ifconfig eth0 up
sudo ifconfig eth1 up
sudo ifconfig wlan0 up

If the name of the network interface is unknown, then look it in “logical name” by typing the command:

sudo lshw -C network

Manual assignment of settings (reset after reboot):

sudo ifconfig eth0 inet 192.168.0.2 netmask 255.255.255.0

For the settings not to be reset, they must be written to the configuration file:

sudo nano /etc/network/interfaces

Example content:

auto lo
iface lo inet loopback

auto eth0
iface eth0 inet static
address 192.168.0.2
netmask 255.255.255.0
network 192.168.0.0
broadcast 192.168.0.255
gateway 192.168.0.1
dns-nameservers 192.168.0.1

auto eth1
iface eth1 inet static
address 10.0.0.2
netmask 255.255.255.0

auto eth2
iface eth2 inet dhcp

In the nano editor, the Ctrl+O key combination is used to save the changes, Ctrl+X to exit.

DNS addresses are added to the configuration file /etc/resolv.conf, each with a new line, thus:

nameserver 192.168.0.1
nameserver 8.8.8.8

You can view / add / remove the default route as follows:

sudo route add default gw 192.168.1.1
sudo route del default gw 192.168.1.1

View the routing table as follows:

sudo ip route show
sudo ip route show 172.16.0.0/16
sudo route
sudo route -n
sudo netstat -rn
sudo cat /proc/net/route

Example of adding routes for the network through the gateway, network interface and route for a specific address through the gateway:

sudo route add -net 172.16.0.0/16 gw 10.0.0.1
sudo route add -net 172.16.0.0/16 dev eth0
sudo route add -host 192.168.0.1 gw 172.16.0.1

For example, with the specified route, you can delete packets:

sudo ip route add blackhole 10.10.0.0/24

You can add routes to a separate table, for example, we will add the default route to everyone, and address 192.168.5.12 will specify your default route:

sudo route add default gw 192.168.1.1
sudo ip rule add from 192.168.5.12 lookup 4
sudo ip route add default via 10.0.2.1 table 4

Restarting Network Services:

sudo /etc/init.d/networking restart

Either restart the server:

sudo reboot

See also:
Ubuntu IP Masquerading (NAT)
Changing TX and RX network interface buffers in Linux

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