Networking LAN Topologies, Devices, and IPv6/IPv4 Troubleshooting

LAN Topologies

Star, Bus, Mesh

Star Topology

All devices connect to a central switch/hub.

Bus Topology

All devices share one backbone cable; one break can take down the network.

Mesh Topology

Every device connects to every other device; great redundancy but expensive and complex.

Switch

Sends data only to the intended recipient (based on MAC address).

Hub

Broadcasts data to all ports → causes collisions and inefficiency.

LAN Without a Router

If not connecting to the Internet, a switch alone can handle communication between local devices.

Copper (Ethernet)

Cheap, short distance (~100m), used for small LANs.

Fiber Optic

Expensive, long distance, very fast, used for large buildings or inter-floor links.

Ethernet Link Lights

Indicate a physical connection between devices. Green light = connected; blinking = data transfer; off = no link.

Network vs. Host

Subnet mask 255.255.255.0 → first 3 octets = network, last = host.

Duplicate IPs

Two devices with the same IP cause conflicts: Network confusion, dropped packets, or connection loss.

Static IP Example

Use a static IP for servers, printers, or routers that need a fixed address.

Subnet Mask Purpose

Helps determine same or different network by comparing IP + mask.

Testing LAN Connection

Use ping command: Check each PC's IP. Run ping [other IP].

IPv6

IPv4 ran out of addresses. IPv6 supports 3.4×10³⁸ addresses.

"::" in IPv6

Double colon (::) means a series of consecutive zeros.

IPv6 Link-Local

Auto-configured (start with fe80::). Used for local communication without a router.

IPv6 Compression

Remove leading zeros and collapse zero blocks (::).

IPv4 Auto-Addressing

Uses DHCP or APIPA (169.254.x.x).

IPv6 Auto-Addressing

Uses SLAAC (Stateless Address Autoconfiguration) — automatic and faster.

First Steps to Troubleshoot

Check physical connections (cables, link lights). Verify IP configuration (using ipconfig). Test connectivity (using ping).

Why Check Cables First?

Most issues are physical—unplugged, broken, or miswired cables. Quick and simple fix!

Ping Command

Tests connectivity and response time to another device. Helps determine if the device is reachable at the network layer.

Packet Tracer

A Cisco tool for simulation and debugging. You can visualize packet flow, find errors, and test without real hardware.

Transport Layer Problem Example

Example: Port blocking or TCP connection failure. Network is fine, but applications can't communicate properly.

Cat5 on Gigabit Network

Cat5 supports only up to 100 Mbps; Gigabit requires Cat5e or Cat6. Using Cat5 causes slow speed or connection issues.

Attenuation

Signal loss over distance. Longer cables = weaker signal = potential errors. Use repeaters or shorter runs.

Crosstalk

Interference between adjacent wires in a cable. Twisting pairs reduces this effect.

Cable Tester vs. Toner

Tester: Checks continuity and pinouts. Toner: Finds where a cable runs in a wall or ceiling. Key Point: Tester = function; Toner = location.

100-Meter Limit

Ethernet standards limit copper runs to 100 meters for reliable speed. Longer runs cause attenuation and timing errors.

Design a Simple LAN

Diagram idea: [Printer1] [Printer2] | +--+---------------+--+ | | Switch | +----+----+----+ | | | PC1 PC2 PC3. Star topology, all connected via a switch.

IP Example

Different network portions (1 vs. 2) with same mask → different subnets. Cannot communicate without a router.

Documentation Steps

Record: IP addresses & subnet masks, Device names and roles, Cable types and ports used, Network diagram, Troubleshooting notes.

Green Link Lights but No Communication

Physical layer is fine → issue is higher up. Likely IP misconfiguration, firewall, or switch settings.

Long-Distance Connection

Choose fiber optic cable. Handles long runs, avoids interference, supports higher speeds.

Extra Study Tips

Practice subnetting! (e.g., 192.168.1.0/24 → 254 hosts). Use ipconfig and ping commands on your PC to visualize how addressing works.

OSI Layers

Remember OSI layers: Please Do Not Throw Sausage Pizza Away (Physical, Data Link, Network, Transport, Session, Presentation, Application).