Chapter 4: Ethernet Standards

Because each 10x jump justified the cost of upgrading cabling and hardware. Intermediate speeds (like 20 Mbps) failed due to lack of demand.

It phased out hubs (half-duplex, collision-prone) in favor of switches (full-duplex, efficient). Hubs are now limited to 10 Mbps networks.

Half-duplex: Devices can’t transmiteceive simultaneously (e.g., CB radios).

Full-duplex: Enabled by 100 Mbps Ethernet; allows simultaneous two-way communication (standard today).

Speed: 100 Mbps

Cabling: Cat3 (used all 4 pairs)

Range: 100m per node

Legacy: Obsolete; required hubs.

Speed: 100 Mbps

Cabling: Cat5 (used 2 pairs)

Duplex: Full-duplex

Legacy: Still called 100BASE-T today.

Medium: Multimode fiber

Range: Up to 2 km

Use Case: Long-distance connections.

A mode where devices can either send or receive data, but not both at the same time (like a CB radio).

A mode where devices can send and receive data simultaneously (like a phone call).

Cat 3 cable using all 4 wire pairs.

It was less efficient and got replaced by better standards like 100Base-X.

Cat 5 cable using only 2 wire pairs.

Full duplex.

100Base-T.

Long-distance connections using multimode fiber, up to 2 kilometers.

1000 Mbps (1 Gbps). Standards are named 1000BASE-[X] (e.g., 1000BASE-T).

Cable: Twinaxial copper (Twinax).

Range: 25 meters.

Legacy: Rarely used; mostly outdated.

Cable: Multimode fiber.

Range: Up to 500 meters.

Use Case: Short-to-medium distances (e.g., within buildings).

Cable: Single-mode fiber.

Range: Up to 5 kilometers.

Use Case: Long-distance connections (e.g., campus networks).

Cable: Cat 5e (minimum), but Cat 6 is ideal.

Range: 100 meters.

Legacy: The most common Gigabit Ethernet standard for LANs.

Cat 6: 55 meters max.

Cat 6a: 100 meters (recommended).

Cable: Multimode fiber.

Range: 26–400 meters (varies with fiber type).

Cable: Single-mode fiber (1310nm wavelength).

Range: 10 kilometers.

Cable: Single-mode fiber (1550nm wavelength).

Range: 40 kilometers.

Same specs (e.g., 10GBASE-LW = 10km range), but LW/EW/SW are designed for SONET networks (backbone internet infrastructure).

1000Base-" followed by a letter or letters indicating the medium (e.g., T, SX, LX, etc.).

An older copper standard using Twinax cable; limited to 25 meters; rare today.

Uses multimode fiber, max distance ~500 meters.

Uses single-mode fiber, max distance ~5 kilometers.

Uses Cat 5e or Cat 6 UTP, max distance 100 meters.

Copper uses standardized RJ45 for all speeds (10Mbps–10Gbps).

Fiber has multiple connector types (LC, SC, ST, MTP) requiring modular transceivers.

Allows interchangeable transceiver modules (e.g., SC, LC, ST) in the same switch.

Vendors (Cisco, Netgear, etc.) agree on standards so modules are cross-compatible.

GBIC: Early modular transceiver for SC/ST connectors.

Larger than modern SFPs; obsolete but still found in legacy gear.

Smaller size for high-density switches.

Supports LC/MTP (small form-factor connectors).

Hot-swappable; used for 1Gbps fiber/copper.

Same physical size but supports 10Gbps.

Backward-compatible with SFP (but at 1Gbps speed).

40Gbps Ethernet (and 100Gbps with QSFP28).

Combines 4x channels in one module for high-speed backbone links.

Uses one fiber strand (vs. duplex).

Different wavelengths (colors) for sendeceive (e.g., 1310nm Tx / 1490nm Rx).

Sold in matched pairs; reduces cabling costs.

LC: Small, latch-based (common with SFP).

SC: Square push-pull (older, used with GBIC).

ST: Bayonet-style (obsolete).

MTP/MPO: Multi-fiber (used for 40G/100G).

Because fiber has many physical connector types (e.g., SC, ST, LC), and flexibility is needed for different use cases.

MSA (Multi-Source Agreement) modular transceivers—interchangeable modules that fit into a standard port.

A pluggable module that transmits and receives optical signals; allows switches to use different fiber connectors.

Gigabit Interface Converter; supported larger connectors like SC and ST.

SFP – Small Form-factor Pluggable transceiver.

SFP+ supports higher speeds (up to 10 Gbps), while SFP typically supports 1 Gbps.

QSFP (Quad Small Form-factor Pluggable) supports 40 Gigabit Ethernet.

Multi-Source Agreement; allows hardware vendors to create interchangeable modules for compatibility.

A transceiver that uses a single fiber strand to both send and receive data using different light wavelengths.

One transceiver sends on wavelength A and receives on B; its pair does the opposite.

They reduce the number of fiber strands required, cutting down on cable complexity and cost.

Single-mode fiber, which supports long-distance, high-speed communication.

Re-terminating is time-consuming and difficult; transceivers make it easy to switch connector types without rewiring.

Creates a broadcast storm (data loops infinitely, crashing the network).

Solution: Spanning Tree Protocol (STP) automatically disables redundant paths to prevent loops.

Attack: Floods switches with fake MAC addresses, filling the CAM table and forcing uncontrolled flooding (like a hub).

Defense: Enable flood guards on switches to detectlock excessive MAC traffic and shut down malicious ports.

No link (if no auto-negotiation) or one-sided link lights (speed mismatch).

Fix: Use auto-sensing switches or replace legacy gear.

Uplink port → Regular port (straight-through cable).

Regular port → Regular port (crossover cable).

Auto-negotiation fails (e.g., one defaults to full-duplex, the other half-duplex).

Fix: Manually set both NICs to half-duplex in Device Manager.

Use high-speed ports as a backbone (e.g., link all 1Gbps ports to a central switch).

Avoid wasting high-speed ports on low-speed links.

A bridging loop occurs, causing infinite data circulation and taking down the broadcast domain.

Spanning Tree Protocol (STP)

It elects a root bridge and disables redundant ports to break the loop.

A Layer 2 attack that floods the switch with MAC addresses, possibly causing a DoS or allowing MITM attacks.

Flood Guard, which detects unusual traffic and disables the port if needed.

The link may fail due to a speed mismatch, often with no link light or mismatched speed indicators.

A crossover cable.

It allows connection to another switch using a straight-through cable without needing a crossover.

Yes, but it’s unnecessary and often seen as a misuse.

Use a crossover cable between two regular ports, or one regular port to an uplink port with a straight-through cable.

Devices can send and receive data at the same time.

When directly connecting two computers with a crossover cable (e.g., on a plane with no network).

Use the 1Gbps ports to create a mini-backbone between them.

It wastes the bandwidth advantage of the gigabit ports.