Lab: Shellshock netcat

The goal of this step is to understand how netcat (nc) works.

Step: 4

Netcat is a program that helps developing and testing network programs.
There are way too many options to discuss here, but we need this tool.
A bit of background
- For the most part, every computer on the internet has an IP address.
  - We can see this by typing ifconfig
  - look for an entry like
```
inet addr: 10.0.2.15 
          
```
  - WRITE THIS DOWN, you will need it multiple times.
  - This will be different on different machines.
  - This number, 10.0.2.15 in this case identifies your machine.
  - This is somewhat of a lie, but live with it for now.
- In addition, each machine supports a number of network ports.
  - Think of the ip address as a building.
  - And the port as a room number.
- For the most part, httpd is on port 80
- https is on port 443
- Look at /etc/services for a standard list of ports.
- Ports below 1024 are special and usually locked.
- We will use port 9090 for our experiments.
Netcat (nc) can act as either a "client" or a "server"
Client demo
- Your machine is running a web server.
- We can talk to that web server using nc
  - $ represents the prompt.
  - 10.0.2.15 is the ip address of the local server.
  - After the nc command type GET index.html
  - ```
  $ nc 10.0.2.15 80
  GET index.html
           
```
- You will see a message that states you are not using http:2.0
Server demo
- nc -l 9090 -v
- This starts netcat listening on port 9090 in verbose mode.
- In a different terminal run a client
  - nc localhost 9090
  - or nc 10.0.2.15 9090
- Notice you can type in the client window and it will be echoed on the server window.
- You can also type in the server window and it will be echoed on the client.
We will use nc in server mode later.