What is an IP Address

An IP Address (or Internet Protocol address) is an address used to uniquely identify a device on an IP network. The address is

made up of 32 binary bits which can be divisible into a network portion and host portion with the help of a subnet mask.

www.nyu.edu = 128.122.108.71 = 10000000.01111010.01101100.01000111

The 32 binary bits are broken into four octets (1 octet = 8 bits). Each octet is converted to decimal and separated by a period (dot). For this reason, an IP address is said to be expressed in

dotted decimal format.

Network (or Subnet) Masks

A network mask helps you know which portion of the address identifies the network and which portion of the address

identifies the node.

Class A, B, and C networks have default masks, also known as natural masks, as shown below.

Class A: 255.0.0.0 (or 11111111.00000000.00000000.00000000)

Class B: 255.255.0.0 (or 11111111.11111111.00000000.00000000)

Class C: 255.255.255.0 (or 11111111.11111111.11111111.00000000)

Default Network - The IP address of 0.0.0.0 is used for the default

Loopback - IP address 127.0.0.1 is used by the host computer to send a message back to itself for

troubleshooting and network testing.

IPv4 and IPv6

Traditional IP addresses are 32-bits long and written in dotted decimal format. These are considered IPv4 format addresses.

172.17.100.203

Since there are only approximately 4.2 billion public IPv4 addresses available (232), the number of available IP addresses will soon be depleted. That is why the world will be switching

over to the IPv6 system soon.

3ffe:1900:4545:0003:0200:f8ff:fe21:67cf

The IPv6 addresses are 128 bits long, written in hexadecimal, and separated by colons (similar to MAC addresses, just longer)

There will be 340,282,366,920,938,463,463,374,607,431,768,211,456

IPv6 addresses available (2128) or approximately 340 Undecillion.

Private IP Addresses

A private IP address is an address that is allowed to travel across an internal network, but not permitted to travel across the Internet. This allows individuals and companies to have a

lot of computers internally, but only require one or more public IP address, preserving the number of available IP addresses.

10.0.0.0 - 10.255.255.255172.16.0.0 - 172.31.255.255

192.168.0.0 - 192.168.255.255

169.254.0.0 through 169.254.255.255 (Automatic

Private IP Addressing only)

Identify Your Public and Private IP Address

If you are using a Windows-based system, use the IPCONFIG command to

display your current TCP/IP configuration details. To run the

IPCONFIG command, start a Command Prompt session (click on Start, then choose [Run], then [Programs], then [Accessories] and finally [Command

Prompt]). You should get a new command window. In this window, type

IPCONFIG and press <Enter>.

If you are using a Mac-based system, the command is IFCONFIG. Click on

[Go], then [Utilities] and then [Terminal]. In the Terminal window,

type the command IFCONFIG.

Follow The OSI Model

In the TCP/IP data flow, the information flows

down and back up following the Open

Systems Interconnection (OSI) Model.

For this class, we are primarily concerned with

Layers 1-4:

Ethernet/Network cables and wireless signals operate at Layer 1.

Switches communicate at Layer 2.

Routers/Firewalls communicate at Layers 3

and 4.

Why Binary and Hexadecimal?

Internet

Follow the path . . . .

Computer

SwitchRouter

Why Binary and Hexadecimal?On the LAN, the wireless or wired Network Interface

Card (NIC) on the computer is identified by the switch by Media Access Control (MAC) Address which is

displayed in hexadecimal format.

Computer Switch

00:10:aa:a1:2b:cce0:f8:47:aa:ba:81

Why Binary and Hexadecimal?

On the LAN, the NIC on the switch is identified by the internal NIC on the router by the MAC Address

01:a0:cc:a4:4e:1100:10:aa:a1:2b:cc

RouterSwitch

Why Binary and Hexadecimal?

Some routers, like the ones that are in the typical home, have a switch and router combined into one device.

Why Binary and Hexadecimal?

On the WAN, the external facing NIC on the router is identified by other computers on the Internet by Internet

Protocol (IP) Address, which is displayed in dotted decimal format, but actually travels across the Internet in

binary format.

128.122.108.7110000000.01111010.01101100.01000111

216.54.111.220

Internet

Router

Why Binary and Hexadecimal?Follow the path . . . .

e0:f8:47:aa:ba:81

10:f3:22:a1:b2:c1

192.168.1.1

128.122.108.71

32.156.253.20192.168.1.200

Test You Network Connectivity

You can test your connection using the PING command. PING is a command line utility that allows you to send an Internet Control Message Protocol (ICMP) request to another machine on the network which hopefully then replies. If the output indicates there is no response then there could be a problem with the

network configuration or that the site is not available to receive PING requests.

To run the PING program from either the Windows or Mac, simply type the ping command and an IP address or Fully Qualified Domain Name (FQDN). that

The format of the PING command is:

ping remote machines IP address followed by <Enter>.

Therefore to PING www.nba.com, whose address is 216.254.95.72, enter

ping 163.1.2.1 and press <Enter> or ping www.nba.com and press <Enter>

If everything is working correctly you should get the response similar to that shown below:

PING a1570.gd.akamai.net (216.254.95.72): 56 data bytes 64 bytes from 216.254.95.72: icmp_seq=0 ttl=49 time=11.725 ms 64 bytes from 216.254.95.72: icmp_seq=1 ttl=49 time=18.069 ms 64 bytes from 216.254.95.72: icmp_seq=2 ttl=49 time=13.014 ms 64 bytes from 216.254.95.72: icmp_seq=3 ttl=49 time=14.956 ms