Introduction to Networking — Introduction to Information and Communication Technology

The address of the building is very much like an IP address you’d have assigned to you by who you pay to get on the internet. The streets and surrounding neighborhood you’re in could be considered a local area network, where each house has it’s own address, and they’re all connected. The State and City or County is your ISP , most ISPs have a local branch that’s for your region, which could be related to your city/county, the full ISP is the State, and the Internet is a country.

Your Local US Postal Service is a set of buildings that route letters and packages between different post offices. Letters and packages go into one Post Office and get routed from that office to a distribution center. The distribution center then sends them to another major distribution center and so on until it reaches the distribution center that serves the remote Post Office nearest its destination. They are then sent to the remote Post Office serving the zip code of the destination address from where they are delivered to their destination.

Let’s start with a building. Buildings can be described in two different ways. They have a physical description, “The Arlington Career Center is a two story cement building of the Brutalist architectural style with a circular driveway in front of its main entrance.” This is a description that is fixed and (fairly) hard to change. On the internet, this would be your computers MAC address . Buildings can also be described by the street address assigned to them by their City or County and the US Postal Service, as in 816 South Walter Reed Drive, Arlington, VA 22204.

The best metaphor to use is how good old fashion snail mail is transferred around and the network of roads crossing the country.

Because the internet feels like smoke and mirrors to a lot of people, a concrete physical metaphor could be very helpful in explaining both the parts of the internet and how it all comes together.

The information from this section is reused throughout the rest of the course.

In reality the internet is tens of thousands kilometers of fiber optic cable, hundreds of thousands to millions of kilometers of copper wire, and hardware and software connecting them all together in a redundant, fast, and self-sufficient network. But not to worry, it’s not that bad: you only have to worry about a very small portion of the network, you can let someone else worry about the rest.

In the broadest terms, people often view the Internet as a cloud. You put your data in one place, and it comes out the place you want it to on the other side, with what happens inbetween obscured in the fog.

The fifth and final layer is the Application layer . This layer refers to higher-level protocols used by most applications for network communication. An example of application layer protocol is FTP (File Transfer Protocol). Data coded according to application layer protocols are then encapsulated into one or more transport layer protocols which in turn use lower layer protocols to effect actual data transfer.

The next layer is the Transport layer . The transport layer’s responsibility is end-to-end message transfer. There are 2 categories of end-to-end message transmission: connection-oriented (TCP) or connectionless (UDP). The transport layer provides this service of connecting applications together through the use of ports. This layer offers reliability and error control.

The next layer is the Network or Internet layer . This layers gets data from a source network to the destination network. This generally involves routing the packets across a network of networks (also known as internetwork). This is where IP (Internet Protocol) comes in. IP performs the basic task of getting packets of data from source to destination.

The next layer is the Data link layer . This layer is used to move packets from the network layer on two different hosts. The process of transmitting packets on a link layer can be controlled in the software device driver for the network card and on firmware. Different protcols are used for different types of networks. Broadband Internet access uses PPPoE as the protocol. For a local wired network, Ethernet is used. For local wireless network, IEEE 802.11 is used.

The first layer is called the Physical layer . This layer is responsible for encoding and transmitting data over network communications media. It operates with data in the form of bits which are sent from the Physical layer of the sending source and received at the Physical layer of a destination source. When you hook up a computer using an Ethernet cable you are connecting that computer on the Physical layer. This Physical layer is the lowest level of the TCP/IP Model.

The TCP/IP Model is a specification for computer network protocls. TCP/IP defines a set of rules to enable computers to communicate over a network. It specifies how data should be formatted, addressed, shipped, routed and delivered to the right destination.

Introduction To Network Addressing¶

Binary¶

For people who have never encountered binary, it can seem a little bit
intimidating. It really isn’t that bad, trust me. Most people learn math in
base 10 in elementary school and learn it through a system that looks something
like this (where H is hundreds, T is tens, and O is ones):

H
T
O

1
8
5

Mathematically those columns look something like this:

102
101
100

1
8
5

So:

1 · 102 + 8 · 101 +
5 · 100 = 185

Right? If the number in the ones column is more than ten, you simply carry the
number over to the number over to the next column like this: if you have 13 in
the ones column you move the 10 into the tens column and leave the 3 in the
ones column. The concept is very similar in base 2. The biggest difference is
that instead of having , , and you have
, , and :

22
21
20

In binary only two numbers are used: 1 and 0, as opposed to the 0-9 in the base
ten system. This is because 1 and 0 are the only numbers that will fit in the
columns. In order to write the number 5 in binary you need to break the number
down. , both 4 and 1 can be easily converted into base two.
and , so you put a 1 in the and
columns, and a 0 in any columns between. This results in a chart
that looks like this:

22
21
20

1
0
1

So the number 5 in binary is 101.

For your reference:

Hex¶

Hexadecimal (otherwise known as hex) is the code that is usually used in web
design as each color is assigned a hex code. It usually looks something like
this: #66CC99. What do the letters mean? The letters are numbers that are 10
and greater. here’s the chart:

Decimal:
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15

Hex:
0
1
2
3
4
5
6
7
8
9
A
B
C
D
E
F

This next part will be very similar to the binary example above. This time
instead of base 2, you’re going to use base 16. So if you do something like
this:

162
161
160

2
F
A

And then crunch the numbers – – we get 762. And no, the 10 and 15 did not show up out of nowhere.
Remember that in hex letters equal numbers. 10 = A and 15 = F.

Sometimes there are hex numbers like 235. Without a symbol in front you can’t
tell if it’s actually 235, or if it’s 565. Here’s how you can tell the
difference: usually there will be either a $ sign, a # sign, or 0x in front of
the number. So $235, #235 and 0x235 are the same hexadecimal number.

IP Addresses¶

An IP address is a number given to a computer (a server or a personal
computer) by the ISP. The most commonly used IP address is a 32-bit (4
byte) address. It looks like this in the decimal system: 172.16.0.1 . This
number is converted from binary because it tends to be easier for humans to
process decimal numbers. In binary the IP address looks something like this:
10101100.00010000.00000000.00000001 – the reason this is a 32-bit address is
because in binary there are 32 characters, and it’s 4 bytes because there are 4
groups of 8. These bytes are also called octets.

So what exactly does this number mean?

The first octet defines the class of the network. The class determines how big
the address space is for the network… in other words, how many computers can
be addressed on the network. A class networks are the largest, and are usually
reserved for governments. B class networks are second largest, and are used by
ISP’s, corporations, school systems and the like. C class networks are the
smallest

A = 0-123 (last 3 octets available for host addressing and subnetting)
B = 124- 191 (last 2 octets available for host addressing and subnetting)
C = 192 – 223 (last 1 octet available for host addressing and subnetting)
D/E = 224 -255 (experimental and testing networks)

EXAMPLE:

If your computer has an address of 158.59.224.135, the address is interpreted
as follows: The computer belongs to a class B network, so the first two octets
define the network. The last two octets define the specific host on the
network, as well as any subnetting.

The first two octets are the IP address assigned by the ISP for all of the
computers in that network. The administrator or the user assigns the last two
octets to the computer. This means you. If you have a network of, lets say,
three computers and your network IP address is 172.16.0.0 you can assign the
first computers IP address to be 172.16.0.1 then the second computer’s IP
address can be 172.16.0.2, and the third can be 172.16.0.3 . This allows you to
keep your network a little more organized.

Give them the IP address of a well-known site as an example.

Important IP addresses¶

• Localhost

127.0.0.1

• Private Addresses
  • 10.0.0.1-10.255.255.254 (10.0.0.0/8)
  • 172.16.0.1-172.31.255.254 (172.16.0.0/12)
  • 192.168.0.1-192.168.255.254 (192.168.0.0/16)

Dynamic IP Addresses¶

Dynamic IP addresses are IP addresses that are not necessarily tied down to one
machine. They are usually applied to personal computers and other devices that
can be taken on an off a network without worrying about disrupting anything
other than being suddenly disconnected while trying to send an e-mail. You will
usually find a dynamic IP address on your personal computer.

Static IP Addresses¶

You are more likely to find a static IP address on a server than on a personal
machine. This is because if the IP address to a server changes it will disrupt
the ability of users to access the site (or sites) hosted on that server.

Domain Name System¶

The Domain Name System (DNS) associates various information with domain names.
It serves as the phone book for the Internet by translating human-readable
computer hostnames (ex: www.openbookproject.net) into IP addresses (ex:
152.19.134.41) which networking equipment needs to deliver information. DNS
also stores other information such as the list of mail servers. DNS is an
essential component of the Internet we use.

DNS makes it possible to assign Internet names to organizations independent of
the physical routing hierarchy represented by the numerical IP address. DNS
distributes the responsibility for assigning domain names and mapping them to
IP networks by allowing an authoritative name server for each domain to keep
track of its own changes, avoiding the need for a central register to be
continually consulted and updated.