Networking Fundamentals: MAC, LLC, and Wi-Fi Security

MAC vs. LLC Sublayers and Frame Addressing

Key Differences Between MAC and LLC

• MAC Sublayer: Compliant with the LAN technical solution as it depends on the physical and medium access protocols.
• LLC Sublayer: Unifies solutions; is independent of the underlying MAC LAN; serves as an interface for upper layers.

Addressing Mechanisms

• MAC Address: Identifies network nodes.
• LLC: Routes the information received by the MAC layer to upper layers.

Understanding Late Collisions in Ethernet

Causes and Effects of Late Collisions

A late collision occurs when a station receives a collision signal too late, typically after it has stopped listening to end the transmission because the segment (plot) was too small. Late collisions can cause lower frames (e.g., 512 bits) to be invalid or tagged, often indicating topology segments smaller than the standard requires.

Sub-1 Gigabit Ethernet Standards and Distances

Physical Environment and Coverage Distances

• 100BASE-TX: Uses UTP Category 5e standards and higher.
• 100BASE-FX (Fiber Optic): Up to 412 meters (or 200 meters in certain configurations).
• Full Duplex Single Mode Fiber: Up to 20 kilometers (20km).

Wireless Network Topologies: Ad-hoc, Infrastructure, and MESH

Ad-hoc vs. ESS Infrastructure Differences

In an Ad-hoc network, there is no need for a central hub or Access Point (AP). Each node is part of a Peer-to-Peer (P2P) network and generally does not allow access to wired networks.

MESH Technology

Mesh technology is used to cover large areas effectively, such as metropolitan or rural areas. It utilizes a mixture of the two existing wireless network topologies (Ad-hoc and Infrastructure). Mesh networks are not based on Access Points acting as gateways; rather, they resemble P2P networks where each customer device acts as a security point of access.

Essential Wi-Fi Security Measures

1. Change Default Administrator Passwords: Wireless devices often come with generic default keys, which can easily facilitate unauthorized access.
2. Employ Strong Security Mechanisms (WPA2/WPA3): Running an open network without encryption allows unwanted access.
3. Enable MAC Filtering: A network without MAC filtering allows any device to associate. Filtering ensures access is granted only to specific, authorized MAC addresses.
4. Change and Hide the SSID: A visible SSID with an attractive name can attract more attacks. Concealing the SSID permits access only to those who know the network name.
5. Limit the Number of Nodes: If you only require a limited number of devices, restrict the maximum number of connections to avoid unwanted access.
6. Disable the DHCP Service: By disabling the DHCP server and using manual (static) IP addresses, only users who know the specific IP addressing scheme can achieve connectivity in case of intrusion.