Lab 10.4.1 IP Addressing Overview

Estimated time: 30 min.

Objectives:

This lab will help you develop an understanding of IP addresses and how TCP/IP networks operate. IP addresses are used to uniquely identify individual TCP/IP networks and hosts (computers and printers) on networks in order for devices to communicate. Workstations and servers on a TCP/IP network are called "HOSTS" and each will have a unique IP address which is referred to as its "HOST" address. TCP/IP is the most widely used protocol in the world. The Internet or World Wide Web uses only IP addressing. In order for a host to access the Internet, it must have an IP address.

In its basic form, the IP address has two parts; a Network Address and a Host Address. The network portion of the IP address is assigned to a company or organization by the Internet Network Information Center (InterNIC). Routers use the IP address to move data packets between networks. IP Addresses are 32 bits long (with current version IPv4) and are divided into 4 octets of 8 bits each. They operate at the network layer, Layer 3 of the OSI model, (the Internetwork Layer of the TCP/IP model) and are assigned statically (manually) by a network administrator or dynamically (automatically) by a Dynamic Host Configuration Protocol (DHCP) Server. The IP address of a workstation (host) is a "logical address" meaning it can be changed. The MAC address of the workstation is a 48-bit "physical address" which is burned into the NIC and cannot change unless the NIC is replaced. The combination of the logical IP address and the physical MAC address help route packets to their proper destination.

There are 5 different classes of IP addresses and depending on the class, the network and host part of the address will use a different number of bits. In this lab you will work with the different classes of IP addresses and become familiar with the characteristics of each. The understanding of IP addresses is critical to your understanding of TCP/IP and Internetworks in general.

Tools / Preparation:

Explanation: There are 5 classes of IP addresses (A thru E). Only the first 3 classes are used commercially. We will discuss a class A network address in the table to get started. The first column is the class of IP address. The second column is the first octet which must fall within the range shown for a given class of address. The class A address must start with a number between 1 and 126. The first bit of a class "A" address is always a zero meaning the High Order Bit (HOB) or the 128 bit cannot be used. 127 is reserved for loop back testing. The first octet alone defines the network ID for a class A network address. The default subnet mask uses all binary ones (decimal 255) to mask the first 8 bits of the class A address. The default subnet mask helps routers and hosts determine if the destination host is on this network or another one. Since there are only 126 class A networks, the remaining 24 bits (3 octets) can be used for hosts. Each class A network can have 2^24 power (2 to the 24th power) or over 16 million hosts. It is common to subdivide the network into smaller groupings called subnets using a custom subnet mask which will be discussed in the next lab.

The network or host or host portion of the address can not be all ones or all zeros. As an example, the class A address of 118.0.0.5 is a valid IP address since the network portion (first eight bits equal to 118) is not all zeros and the host portion (the last 24 bits) is not all zeros or all ones. If the host portion were all zeros it would be the network address itself. If the host portion were all 1's it would be a broadcast for the network address. The value of any octet can never be greater than decimal 255 or binary 11111111.

Cls	1st Octet Decimal Range	1st Octet High Order Bits	Network / Host ID (N=Network, H=Host)	Default Subnet Mask	Number of Networks	Hosts per Network (usable addresses)
A	1 – 126*	0	N.H.H.H	255.0.0.0	126 (27 – 2)	16,777,214 (2 24 – 2)
B	128 – 191	1 0	N.N.H.H	255.255.0.0	16,382 (214 - 2)	65,534 (2 16 – 2)
C	192 – 223	1 1 0	N.N.N.H	255.255.255.0	2,097,150 (221 – 2)	254 (2 8 – 2)
D	224 – 239	1 1 1 0	Reserved for Multicasting
E	240 – 254	1 1 1 1 0	Experimental, used for research

* Class A address 127 cannot be used and is reserved for loopback and diagnostic functions

Step 2 – Basic IP Addressing.

Task: Use the IP address chart and your knowledge of IP address classes to answer the following questions.

1. What is the decimal and binary range of the first octet of all possible class "B" IP addresses?
   Decimal: From: ________ To: ________
   Binary: From: ________ To: ________
   
2. Which octet(s) represent the network portion of a class C IP address? ______________
   
3. Which octet(s) represent the host portion of a class "A" IP address? ________________

Task: With the following IP host addresses, indicate the Class of each address, the Network Address or ID, the Host portion, the Broadcast Address for this network and the default Subnet Mask.

Explanation: The host portion will be all zeros for the network ID. Enter just the octets that make up the host. The host portion will be all ones for a broadcast. The network portion of the address will be all ones for the subnet mask.

1. Fill in the following table:

Host IP Address	Addr. Class	Network Address	Host Address	Network Broadcast Address	Default Subnet Mask
216.14.55.137
123.1.1.15
150.127.221.244
194.125.35.199
175.12.239.244

2. Given an IP address of 142.226.0.15
1. What is the binary equivalent of the second octet? ___________________
2. What is the Class of the address? _________________________________
3. What is the network address of this IP address? ____________________
4. Is this a valid IP host address (Y/N) ? _____________________________
5. Why or why not?

   
   
   
   
   

3. Which is the maximum number of hosts you can have with a class C network address? ______
   
4. How many class B networks are there? _____________
   
5. How many hosts can each class B network have ? ______________
   
6. How many octets are there in an IP address? ________ How many bits per octet? ________