Data Link Layer

What is a MAC Address?

A MAC (Media Access Control) address is a 48-bit hardware identifier burned into a network interface card by its manufacturer, used to identify a device unique…

What is ARP (Address Resolution Protocol)?

ARP (Address Resolution Protocol) maps a known IP address to its corresponding MAC address on a local network, allowing a device to discover the physical hardw…

Router vs Switch: What is the Difference?

A switch connects devices within a single local network and forwards frames between them using MAC addresses, while a router connects separate networks togethe…

What is the Data Link Layer (OSI Layer 2)?

The Data Link layer is OSI Layer 2 — it packages raw bits from the Physical layer into structured frames, adds MAC addresses for local delivery, and detects (t…

VLAN Trunking Explained

A VLAN trunk is a single physical link between two switches (or a switch and a router) that carries tagged traffic for multiple VLANs simultaneously, using 802…

What is STP (Spanning Tree Protocol)?

Spanning Tree Protocol is a Layer 2 protocol that prevents bridging loops in a switched network with redundant physical links by logically blocking enough port…

MAC Address vs IP Address

A MAC address is a fixed, hardware-burned Layer 2 identifier used to deliver frames within a local network segment, while an IP address is a logical, reassigna…

Hub vs Switch vs Router: What Is the Difference?

A hub is a dumb Layer 1 device that repeats every incoming signal out of all its other ports, a switch is a smart Layer 2 device that reads MAC addresses to fo…

What is a Collision Domain?

A collision domain is the set of network devices whose transmissions can collide with each other because they share the same physical medium at the same time,…

What is a Broadcast Domain?

A broadcast domain is the set of devices that all receive a broadcast frame sent by any one member of the group — every host in the same broadcast domain gets…

What is a VLAN?

A VLAN (Virtual Local Area Network) is a logical grouping of switch ports into a separate broadcast domain, letting devices on different physical switches (or…

What is Link Aggregation?

Link aggregation combines multiple physical network links between two devices into a single logical link, increasing available bandwidth and providing redundan…

What is a Network Interface Card (NIC)?

A Network Interface Card (NIC) is the hardware component — a physical card, onboard chip, or virtual adapter — that connects a device to a network, handling th…

What is Ethernet?

Ethernet is the family of wired networking standards (IEEE 802.3) that defines how devices on a local area network physically connect and frame data at the Phy…

What is the Ethernet Frame Format?

An Ethernet frame is the Layer 2 container that carries data across a local network, made up of a preamble, destination and source MAC addresses, an EtherType/…

What is CSMA/CD?

CSMA/CD (Carrier Sense Multiple Access with Collision Detection) is the media access method used on legacy shared Ethernet segments where a device listens befo…

What is CSMA/CA?

CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) is the media access method used in Wi-Fi (802.11) where a device senses the channel, waits a r…

What is a Network Bridge?

A network bridge is a Layer 2 device that connects two or more network segments and selectively forwards Ethernet frames between them based on learned MAC addr…

What is EtherChannel?

EtherChannel is a link-aggregation technology that bundles multiple physical Ethernet links between two switches (or a switch and a server) into a single logic…

What are Jumbo Frames?

Jumbo frames are Ethernet frames carrying a payload larger than the standard 1500-byte MTU — typically up to 9000 bytes — used to reduce per-packet overhead an…

What is ARP Spoofing?

ARP spoofing (also called ARP poisoning) is an attack where a malicious device sends forged ARP replies onto a local network, falsely associating its own MAC a…