If you need to add proxy of your network in a reboot-persistent way, edit:

sudo vim /etc/environment

Press i and after the row with PATH variable insert:

http_proxy=http://<proxy_server>:<port>/
https_proxy=http://<proxy_server>:<port>/
ftp_proxy=http://<proxy_server>:<port>/

Then press ESC, enter : and write wq! for save and exit from vim.

If you need to use wget, add the same three rows to (eventually uncommenting them inside the file):

sudo vim /etc/wgetrc

If you want to show active network interfaces, type:

ifconfig

If you want to show also network interfaces that are down, type:

ifconfig -a

You could use ethtool, but they are not going to be reboot persistent. If you want to achieve this, edit the following file:

sudo vim /etc/network/interfaces

And edit the file with needed informations:

auto <interface_name>
iface <interface_name> inet static
address <ip_address>
netmask <netmask>
network <network>
gateway <gateway>
dns_nameservers <server_1> <server_2> <server_n>
dns_naesearch <server_name>

Then restart interface to make changes running:

sudo ifdown <interface_name> && sudo ifup <interface_name>