12-TCP/IP Layer 2
- Theory Shall continue…
- Talking today about Layer 2
	- Internet Protocol
		- IP
	- Focused on getting information from one Computer to another anywhere else over the internet
- Today, going to focus on Defining 3 very important terms:
	- IP address
	- Netmask
	- Router/default router/default gateway
- The internet started off using IPv4, or the Internet Protocol version 4
	- running out of addresses, since the internet is bigger than anyone thought it would ever get
	- eventually moving to IPv6
		- going to ignore this for now
- Also going to ignore a new invention to circumvent this shortness of IP addresses, called NAT
	- Network Address Translation
	- going to cover this in a later show, but will ignore it for now for simplicity's sake
- IP Address
	- unique address for each machine on the internet
	- Whole point of the internet is to get information between IP addresses
	- What do they look like?
		- To us, four, 3 digit, numbers, between 0-255, separated by dots
			- xxx.xxx.xxx.xxx
			- anywhere from 0.0.0.0 to 255.255.255.255
		- To a computer, 4 binary numbers, without the dots
	- IP addresses cannot have values higher than 255
		- *GEEK TIP*
			- Why? Because 255 is the greatest value one byte can hold.
- Routers don't and can't remember where each Individual IP address is
	- they break the internet up into chunks
	- e.g.
		- All the IP addresses with Bart's Irish ISP are over there >>>
		- All the IP addresses with Verizon are over there ^^^^
		- etc.
	- They do this with Two Important Numbers
		- Net address
		- Net mask
	- Net addresses are related, i.e., in the same chunk, if they start with the same numbers
		- Netmasks tell us how much of the IP address is related
			- looks like an IP address, but with only 255 and 0
			- a 255 says what is the same
			- a 0 says what can be different
				- e.g. 255.255.0.0
	- Common Subnets
		- Class C
			- all but the last numbers are the same
				- xxx.xxx.xxx.5 and xxx.xxx.xxx.6
				- subnet = 255.255.255.0
		- Class B
			- first two numbers have to be the same
			- xxx.xxx.5.7 and xxx.xxx.8.4
			- subnet = 255.255.0.0
	- Can be more than that, but those are the only ones you are likely to see
	- Router will assign each machine in your house a related IP address
		- the part of your subnet mask that is a 0 is the part that will be different
- Computers distinguish between IP addresses that are on the local network, and those that are elsewhere on the internet
	- those packets for the internet are sent to your router/default router/default gateway
- Bart Busschots
	- bartb.ie <http://bartb.ie/>
	- impodcast.tv <http://impodcast.tv/>
	- podfeet.com <http://podfeet.com/>