Lets suppose you made some changes on your OS configuration that require the reload of the network services,
for example you made a change on your /etc/hosts file

This two basic commands are needed in order to reach the goal

First type:
sudo sh

Give the root password

And then type:

sudo ifconfig en0 down

and then to start it back up type

sudo ifconfig en0 up


This basically restarts your nic adapter which in essence will reload the basic network configration thus reading the changes
you made like in the /etc/hosts file.

Felipe