Computer Networks

LECTURE # 9

MAC ADDRESSING

Introduction to MAC Addressing�

Media Access Control (MAC) addressing is a fundamental concept in network communications, particularly in local area networks (LANs). A MAC address is a unique identifier assigned to network interfaces for communications on the physical network segment.

Objectives of the Lecture

1. Understand what a MAC address is and its purpose.
2. Learn about the structure of a MAC address.
3. Explore how MAC addresses operate in various networking protocols.
4. Discuss the importance of MAC addresses in network security.

What is a MAC Address?

A MAC address (Media Access Control address) is a hardware address that uniquely identifies a device on a network. Unlike IP addresses, which can change depending on the network, MAC addresses are fixed and assigned to a network interface card (NIC) by the manufacturer.

Key Features of a MAC Address�

1. Unique: Each device on a network should have a unique MAC address to avoid conflicts.
2. Physical Addressing: Works at the data link layer (Layer 2) of the OSI model, allowing devices to communicate within the same network.
3. Format: Typically represented as a sequence of hexadecimal digits.

Structure of a MAC Address�

A MAC address consists of 48 bits (or 6 bytes), commonly formatted in several ways:

Example Formats:

1. Hexadecimal or Colon-Separated : `00:1A:2B:3C:4D:5E`

3. Dot-separated: `001A.2B3C.4D5E`

 Breakdown of a MAC Address

1. OUI (Organizationally Unique Identifier): The first three bytes (24 bits) represent the manufacturer of the device. This is assigned by the IEEE(Institute of Electrical and Electronics Engineers)
2. NIC-specific Identifier: The last three bytes (24 bits) are assigned by the manufacturer, ensuring uniqueness within their devices.

Purpose of MAC Addresses�

1. Uniqueness: Identifies devices on a network uniquely, preventing data collisions and ensuring correct data delivery.

2. Data Link Layer Communication: Facilitates communication between devices within the same local network by providing a way to address frames.

3. Network Management: Allows network administrators to manage devices, troubleshoot connectivity issues, and implement network policies.

MAC Addressing in Networking Protocols

1. Ethernet

• In Ethernet LANs, MAC addresses are crucial for data frames. When devices communicate:
• The sending device encapsulates data into frames, specifying the source and destination MAC addresses.
• Switches use MAC addresses to forward frames only to the intended destination.

2. Wi-Fi (Wireless LAN)

MAC addressing plays an essential role in wireless networks. Each device connects to access points using its MAC address. Wireless protocols, such as IEEE 802.11, leverage MAC addresses for the following:

• Authentication: Networks can filter devices based on known MAC addresses.
• Data Transmission: Frames exchanged over the air include MAC addresses to ensure the correct destination.

3. ARP (Address Resolution Protocol)

When a device wants to communicate with another device using IP addresses, it needs to know the MAC address corresponding to the IP. ARP performs this function:

• It broadcasts a request for the MAC address of a specified IP on the LAN.
• The device with the corresponding IP address replies with its MAC address.

Importance of MAC Addresses in Network Security�

MAC addresses can be crucial in constructing network security policies. Some common applications include:

1. MAC Filtering

Network devices, especially Wi-Fi access points, can enforce security by allowing or denying access based on MAC addresses. This practice involves:

• Whitelisting: Only allowing known MAC addresses.
• Blacklisting: Blocking specific MAC addresses from accessing the network.

2. Intrusion Detection and Prevention

Since MAC addresses are fixed identifiers, anomaly detection systems can monitor traffic for unusual patterns, based on known MAC addresses.

 3. Tracking and Management

Organizations can track devices connected to their networks and maintain records based on MAC addresses for auditing and compliance purposes.

Limitations of MAC Addresses

While MAC addresses have their advantages, they also present some limitations:

• Spoofing: Attackers may spoof MAC addresses to gain unauthorized access or impersonate legitimate devices.
• No Routing: MAC addresses operate only on local networks; they are not used for routing traffic across different networks, where IP addresses are required.
• Privacy Concerns: MAC addresses can be used to track devices in public networks, raising privacy issues.

Thank You