Layer 2 and 3 Addressing

Dr. Alexios Louridas

Index

Mac Address

ARP protocol

IP addressing

Clients

How a NIC is identified?

These addresses are hardcoded into the hardware by the manufacturer and serve as a permanent identifier for the device within a network segment. ​

Are MAC addresses UNIQUE?

  • Device Identification:

    • Each network interface controller (NIC) has a unique MAC address.
    • It acts like a digital fingerprint for devices, allowing them to be identified within a network segment.
    • When data packets travel across a network, routers and switches use MAC addresses to direct them to the correct destination.

  • Address Resolution:

    • In local networks, devices communicate using MAC addresses.
    • When a device wants to send data to another device, it first resolves the recipient’s IP address to its corresponding MAC address using the Address Resolution Protocol (ARP).
    • ARP maintains a mapping between IP addresses and MAC addresses.

  • Access Control:

    • Wi-Fi routers and switches use MAC addresses for access control.
    • By filtering based on MAC addresses, network administrators can allow or deny specific devices from connecting to the network.
    • This is useful for securing Wi-Fi networks and preventing unauthorized access

Reasons of MAC Address 

  • Privacy and Security:

    • Changing your MAC address can enhance privacy. By using a different address, you make it harder for others to track your device.
    • Some public Wi-Fi networks may restrict access based on MAC addresses. Changing it allows you to bypass such restrictions.

  • Network Troubleshooting:

    • If you encounter network issues, altering the MAC address can help diagnose problems.
    • It allows you to simulate a different device on the network, which can reveal whether the issue is specific to your hardware.

  • Avoiding IP Conflicts:

    • In some cases, multiple devices on the same network segment might accidentally have the same IP address.
    • Changing the MAC address ensures that your device gets a unique IP address from the DHCP server.

  • Testing and Development:

    • Developers and network administrators often need to test network configurations.
    • Changing the MAC address allows them to simulate different devices without physically swapping hardware.

  • Spoofing and Anonymity:

    • MAC address spoofing is used for anonymity or to bypass network restrictions

Reasons to change MAC Address

  • DHCP and IP Assignment:

    • DHCP servers assign IP addresses dynamically to devices when they join a network.
    • They use the device’s MAC address to ensure consistent IP assignments.
    • This simplifies network management and prevents IP conflicts.

  • Virtualization and Cloning:

    • In virtual environments, virtual machines (VMs) often share the same physical NIC.
    • Each VM has a unique MAC address, allowing them to function independently.
    • Cloning VMs involves changing their MAC addresses to avoid conflicts.

More Reasons to change MAC Address 

Address Resolution Protocol (ARP)

  • ARP connects an ever-changing Internet Protocol (IP) address to a fixed physical machine address, also known as a media access control (MAC) address, within a local-area network (LAN).

ARP operates between the data link layer (MAC address) and the network layer (IP address).

How does ARP work

  • When a new computer joins a LAN, it receives a unique IP address.
  • When data packets arrive at a gateway, the gateway asks ARP to find the matching MAC address for a given IP address.
  • ARP maintains an ARP cache with IP-to-MAC address mappings.
  • If the translation already exists, no new request is made. Otherwise, ARP performs the translation.
  • ARP caches are dynamic and limited in size, ensuring privacy and security.
  • Purpose: Static entries are manually configured and kept in the cache table on a permanent basis.
  • Use Case:
    • Ideal for devices that need to communicate with other devices regularly within the same network.
    • These entries remain unchanged unless explicitly modified by an administrator.
  • Reliability:
    • Static entries serve as a reliable record of specific IP-MAC address mappings.
    • They persistently link an IP address to a MAC address.
  • Management:
    • Requires manual intervention to create and maintain.
    • Useful for critical devices like servers or network infrastructure components.

STatic

ARP CACHING

  • Purpose: Dynamic entries are automatically added by the network device (such as a router or switch) and have a limited lifespan in the cache.
  • Creation Process:
    • When a device wants to communicate with an IP address, it performs an ARP request.
    • The request broadcasts to the local LAN, asking, “Who has IP address X, and what is your Ethernet MAC address?”
    • The responding device provides its MAC address, and the entry is added to the dynamic ARP cache.
  • Lifespan:
    • Dynamic entries remain in the cache as long as they are actively used.
    • If an entry remains unused for a certain period (the ARP cache timeout), it is removed.
  • Benefits:
    • Dynamic entries adapt to network changes and are more flexible.
    • They minimize management overhead compared to static entries.

Dynamic