🔌🌐 Ethernet and Networking Essentials
Learn the basics of Ethernet, standards, frame structure, cable types, devices, and how switches connect.
⚡ Ethernet and Networking Essentials
Ethernet is the most widely used technology in local area networks (LANs). It defines how devices communicate over wired networks using cables and frames.
🌐 What is Ethernet?
Ethernet is a set of standards defined by IEEE 802.3 that specify how data is formatted and transmitted across a wired LAN.
📋 IEEE 802.3 Ethernet Standards
The IEEE 802.3 standard defines Ethernet—the most widely used wired LAN technology. Over time, several extensions and amendments have been added to support faster speeds, new media types, and advanced features.
Here’s a breakdown of important IEEE 802.3 versions:
| Standard | Year | Description |
|---|---|---|
| 802.3 | 1983 | Original 10 Mbps Ethernet over coax (Thicknet) |
| 802.3a | 1985 | 10BASE2 (Thin Ethernet) |
| 802.3i | 1990 | 10BASE-T (Twisted-pair Ethernet) |
| 802.3u | 1995 | Fast Ethernet (100 Mbps, 100BASE-TX) |
| 802.3z | 1998 | Gigabit Ethernet over fiber (1000BASE-X) |
| 802.3ab | 1999 | Gigabit Ethernet over copper (1000BASE-T) |
| 802.3ae | 2002 | 10 Gigabit Ethernet (10GbE) over fiber |
| 802.3an | 2006 | 10GBASE-T (10 GbE over twisted-pair copper) |
| 802.3ba | 2010 | 40 GbE and 100 GbE standards |
| 802.3bj | 2014 | 100 GbE over backplanes and copper cables |
| 802.3bw | 2015 | 100BASE-T1 for automotive and industrial use |
| 802.3bz | 2016 | 2.5GBASE-T and 5GBASE-T over existing cabling |
| 802.3by | 2016 | 25GBASE-R Ethernet over single-lane 25 Gbps |
| 802.3cd | 2018 | 50GBASE, 100GBASE, 200GBASE Ethernet |
| 802.3cu | 2020 | 100GBASE-VR and 400GBASE-VR Ethernet |
| 802.3ck | 2021 | 100G/200G/400G Ethernet over electrical lanes |
| 802.3db | 2022 | Short reach optical interconnects for 100G+ |
ℹ️ Note: Each sub-standard addresses enhancements like speed, media type (fiber, copper), connector types, or low-power applications.
🧠 Easy Tip:
Think of IEEE 802.3 as the main Ethernet umbrella, and its variants like 802.3i or 802.3u as children specializing in different speeds and media.
📦 Ethernet Frame Structure
An Ethernet frame is the basic unit of data transmitted. It contains control and payload information.
🧩 Frame Fields
- Preamble (7 bytes): Sync bits to help receiver prepare
- Start Frame Delimiter (1 byte): Marks the start
- Destination MAC (6 bytes): Who receives the frame
- Source MAC (6 bytes): Who sent it
- Type/Length (2 bytes): Type of protocol (IPv4, IPv6, etc.)
- Data (46–1500 bytes): Actual payload
- Pad: Optional padding if data < 46 bytes
- FCS (Frame Check Sequence): CRC for error checking
📦 Jumbo Frame
- Larger than 1500 bytes (up to 9000 bytes)
- Used in data centers and storage networks
🔧 Terminating Twisted Pair Cables
To build or repair cables, you need the right tools and standards.
🧰 Tools & Components
- Crimping Tool – Attaches connectors to cable ends
- Cable Tester – Checks wiring and signal
- RJ-45 Connector (8P8C) – Common Ethernet plug
- RJ-25 Connector – 6-position connector used for telephony
🎨 Color Coding Standards
- TIA/EIA-568A
- TIA/EIA-568B (most common)
🔁 Cable Types
| Cable Type | Usage |
|---|---|
| Straight-Through | PC to Switch/Router |
| Crossover Cable | PC to PC or Switch to Switch |
| Rollover | Cisco console cable (rare) |
🖥️ Networking Applications
| Device | Function |
|---|---|
| Router | Connects multiple networks, routes traffic |
| Firewall | Controls access to/from networks based on rules |
| IDS (Intrusion Detection System) | Detects suspicious activity (passive) |
| IPS (Intrusion Prevention System) | Detects & blocks attacks (active) |
| IDPS | Combined IDS + IPS |
| Proxy Server | Acts as intermediary between client and internet |
| Load Balancer | Distributes traffic among multiple servers |
| NAS (Network Attached Storage) | File-level storage on network |
| SAN (Storage Area Network) | Block-level high-speed storage |
❗ False Positive vs False Negative
- False Positive: Alert triggered, but no real threat
- False Negative: Threat happened, but no alert (very dangerous)
🔀 Switches vs Hubs
| Feature | Hub | Switch |
|---|---|---|
| Ports | Multi-port repeater | Smart port forwarding |
| Traffic Method | Broadcast to all ports | Sends only to destination MAC |
| Speed | Shared bandwidth | Dedicated per port |
| Efficiency | Low (uses CSMA/CD) | High (MAC table learning) |
🔁 CSMA/CD (used in hubs)
- Carrier Sense Multiple Access with Collision Detection
- Devices listen before sending and retry if collision happens
🔁 Connecting Switches
🛠 MDI vs MDI-X
- MDI (Medium Dependent Interface) – Used on computers
- MDI-X (MDI Crossover) – Used on switches
- Old switches required crossover cables; now most support Auto-MDI-X
🔁 Switching Loops
When two switches are connected in a loop, it can cause:
- Infinite looping of frames
- Network flooding (broadcast storm)
- 🔥 Complete outage
🧠 Solution: Spanning Tree Protocol (STP)
- STP prevents loops by disabling redundant links
- Uses BPDU (Bridge Protocol Data Units) to detect loops
🧠 Mastering Ethernet is key to understanding how devices communicate in wired networks. Learn the frame, cable types, and device roles for a solid foundation.