Data communication occurs between a sender endpoint and one or more receiver endpoints on a network; therefore, learning the details of endpoint identification is essential to understanding the subject. At both the data‐ link layer and network layer, an endpoint is identified by an address that is unique within a communication domain. The data‐ link layer address is commonly referred to as the Media Access Control (MAC) address, because both the de‐facto wired and wireless LAN protocol suites – Ethernet    and Wi‐ Fi – use MAC addresses to identify each endpoint.

The network layer address is commonly referred to as an IP address, because the       Internet Protocol (IP) is the de‐facto network layer protocol on most networks. More specifically, the most widespread network layer protocol in use today is IP version 4, often written as “IPv4” . IP version 6, often written as “IPv6”, is designed to be the      replacement for IPv4 and has been available for some time; however, IPv6 has yet to replace IPv4 at a global level.

LAB OBJECTIVES

The objectives of this lab are:

to give you a working knowledge of representing MAC addresses in binary and

enhanced hexadecimal notations, and converting between the two.

to give you a working knowledge of extracting the Organizational Unique

Identifier (OUI) from a MAC address.

to give you a working knowledge of representing IPv4 addresses in binary and

dotted decimal notation.

LAB SUBMISSION

Use the submission template provided in the assignment inbox to perform the steps requested by this lab. Return to the assignment inbox to submit your lab.

Section One ‐ MAC Address Representation

In this section, we learn how to represent Media Access Control (MAC) addresses at the data‐ link layer.

Computers and devices connect to local area networks with network adapters, which     come in many forms. One common form is a card that can be internally installed onto    the device or computer. This card is termed a Network Interface Controller or Network  Interface Card (NIC). Another common form is as circuitry of the motherboard, so that   the computer or device is network enabled without the need to install an additional       card. Some adapters are external, including those that connect via a USB port. External  adapters allow computers and devices to gain network connectivity without the need to internally install a NIC. Due to the ever increasing demand for virtual machines, virtual   network adapters, which are adapters that exist in software only, are becoming               increasingly common.

While network adapters come in many forms, it is most important that you understand that network adapters enable a computer or device to access a local area network, and  that all network adapters are preconfigured with a MAC address. Manufacturers assign  the address to physical adapters, while software assigns the MAC for virtual adapters.    The MAC address for many physical adapters cannot be modified, though some physical adapters’ addresses can be modified via software. Virtual adapters’ addresses allow        modification of the MAC address via software.

Though a MAC address consists of many details and nuances, its quintessence is a series of bits used to uniquely identify a communication endpoint. The address assigned to       one network adapter will be different than all other addresses within the same                communication domain. Therefore, as long as a sending node knows the MAC address   of its intended recipient, the node can send a message specifically to the one recipient.  A node sending to another node using a MAC address can be likened to your experience of mailing a letter. You know to whom you would like to send the letter, and so you        write the correct address on the envelope and mail it. The address you put is different   from all other addresses, so you know your letter will arrive at the correct place.

Before we look at more details of the 48‐ bit MAC addresses, let us first examine our        numbering system and how this relates to binary numbers. The numbering system we     are familiar with is more formally termed a decimal, or base ten, numbering system. We use ten symbols – 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 – to represent numbers zero through nine. For numbers higher than nine, we concatenate these numeric symbols with the recognition  that each concatenated digit is multiplied by a successive power of 10. For example, the symbol “3” literally means “three”, but the concatenated symbols “23” do not literally    mean “two three” . Rather, they mean “two times ten plus three”, which is twenty‐three. Similarly, “423” does not mean “four two three”, but instead “four times one‐ hundred plus two times ten plus three”, which is four‐ hundred‐twenty‐three. The     meaning of 423 in decimal is illustrated in the following figure.

The Meaning of 423 in Decimal

4 hundreds (4 * 10 2) +

2 tens (2 * 10 1)

3 ones

+ (3 * 10 0)

The binary numbering system is a base two numbering system. Two symbols are used – 0 and 1 – to represent numbers zero and one. For numbers higher than one, the             symbols are concatenated with the recognition that each concatenated binary digit       (termed a “bit”) is multiplied by a successive power of two. For example, the binary       number 101 does not literally mean “one zero one”, but means “one times four plus      zero times two plus one” . The meaning of 101 in binary is illustrated in the following      figure.

The Meaning of 101 in Binary

1 four 0 twos 1 one (1 * 22 ) + (0 * 21 ) + (1 * 20 )

It is important to understand that digital computers and computer networks use binary numbers to represent all data, including the data‐ link layer addresses for network          adapters.

Network adapters are most commonly assigned 48‐ bit identifiers defined as EUI‐48          identifiers by the IEEE Standards Association (EUI stands for Extended Unique Identifier). The first 24 bits of an EUI‐48 identifier comprise the Organizational Unique Identifier       (OUI). An organization that manufactures network adapters obtains this OUI from the     IEEE Standards Association, which ensures that each OUI is unique. To create the MAC    address for a network adapter, the organization combines their OUI with a unique 24‐ bit number to create the 48‐ bit MAC address. Thus, the uniqueness of each OUI when           compared to all other OUIs, combined with the uniqueness of the 24‐ bit extension           assigned by the organization, ensures that any MAC address assigned by a manufacturer is unique throughout the world. The common MAC address form is illustrated in the following figure.

Common MAC Address Form (EUI‐48)

Organizational Unique Identifier (OUI)

Assigned by IEEE

24 bit Extension Identifier

Assigned by Organization

It is worth noting that there is some movement toward manufacturers assigning a 64‐ bit identifier, termed EUI‐64, to their network adapters. However, the most common            assignment today is that of an EUI‐48 identifier. IPv6 supports converting EUI‐48              identifiers into EUI‐ 64 identifiers, but that is beyond the scope of this lab.

To simplify their representation, MAC addresses are commonly represented using            hexadecimal notation in networking texts and tools. This is because it is difficult for          human beings to work with 48‐ bit addresses when they are represented as a series of 48 0s or 1s.

Hexadecimal is a base sixteen numbering system. Sixteen symbols are used – 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F – to represent numbers zero through fifteen. As you might now predict, when we concatenate these symbols, the implicit meaning is that each      symbol is multiplied by a successive power of 16. For example, the symbol “F” literally   means “fifteen”, but the symbols “A3F” means “ten times two‐ hundred‐fifty‐six plus      three times sixteen plus fifteen” . The meaning of “A3F” is illustrated in the following      figure.

The Meaning of A3F in Hexadecimal

10 two ‐ hundred‐ fifty‐sixes (10 * 16 2 ) +

3 sixteens

(3 * 161 ) +

15 ones

(15 * 16 0 )

MAC addresses are represented using hexadecimal digits, where pairs of hexadecimal digits are separated by a colon or a dash. For example the address                                   101010110011010110011101011001011101011111101011 would be represented as AB:35:9D:65:D7:EB or AB‐35‐9D‐65‐ D7‐ EB.

Do not worry if the MAC address representation seems confusing. The focus of this     section in the lab is on EUI‐48 identifier representation of MAC addresses, and how to interpret and understand these addresses in binary and hexadecimal.

1. Let us start with just a portion of a MAC address, for the purpose of learning. Imagine that the first eight bits of a MAC address are 10110010. What is this number in           decimal? In order to determine this, we simply fill in the following table, which has    the powers of two filled in.

All we need to do is to fill in the bit cells from our given binary number, then add the corresponding power of 2 where the bit is 1. When the bit is 0, that power of 2 is not added to the amount.

To start by entering 0 in the leftmost “Cumulative Amount” cell, then we enter a 1 in the leftmost “Bit” cell, which then adds 128 to the cumulative amount, like so:

We then continue following this methodology with rest of the table cells. When doing so, we arrive at the final number 178, so we know that the binary number 10110010 is 178 in decimal.

2. Now, give it a try by converting the binary number 01110110 to decimal by filling in the same table in step 1.

3. Now that we know how to convert the binary number to decimal, let us consider how to do the reverse. If you are given a decimal number, such as 215, how would you go about converting it? We can make use of the similar table below, which helps us by illustrating the powers of 2, as well as the amount remaining we have left to             represent as we add bits to the representation.