Network Topologies & Devices

🤔 Network Topologies

A topology is the physical or logical arrangement of devices in a network. Think of it like floor plans for different buildings.

flowchart TB
    subgraph Star[Star Topology<br/>Most common - Home/Office WiFi]
        S1[Device] --- Center[Switch / Router]
        S2[Device] --- Center
        S3[Device] --- Center
        S4[Device] --- Center
    end

    subgraph Mesh[Mesh Topology<br/>High reliability - Data centers]
        M1[Server] --- M2[Server]
        M1 --- M3[Server]
        M1 --- M4[Server]
        M2 --- M3
        M2 --- M4
        M3 --- M4
    end

    subgraph Bus[Bus Topology<br/>Old - Coaxial cable networks]
        B1[Device] --- Cable((Cable))
        B2[Device] --- Cable
        B3[Device] --- Cable
    end

    style Star fill:#3b82f6,color:#fff
    style Mesh fill:#10b981,color:#fff
    style Bus fill:#f59e0b,color:#fff

Topology	How it works	Pros	Cons
Star	All devices connect to a central switch/router	Easy to manage, one failure doesn’t take down others	Switch fails → whole network down
Mesh	Every device connects to every other device	Extremely reliable, redundant paths	Expensive (lots of cabling)
Bus	All devices share a single cable	Cheap, simple	One break kills the whole network
Ring	Devices form a circle	Fair access to all	One break disrupts entire ring

📡 Network Devices

Devices that make networks work:

flowchart TB
    subgraph Devices[Network Devices]
        HUB[Hub<br/>Broadcasts to all ports<br/>Dumb - no filtering]
        SWITCH[Switch<br/>Sends only to the right port<br/>Smart - uses MAC addresses]
        ROUTER[Router<br/>Connects different networks<br/>Uses IP addresses]
        MODEM[Modem<br/>Connects to ISP<br/>Converts signals]
        AP[Access Point<br/>Broadcasts WiFi<br/>Connects wireless devices]
    end

    subgraph WhereUsed[Where They Live]
        HOME[Home Network]
        OFFICE[Office Network]
        ISP[ISP / Internet]
    end

    HUB --> HOME
    SWITCH --> OFFICE
    ROUTER --> HOME
    ROUTER --> OFFICE
    MODEM --> ISP
    AP --> HOME

    style Devices fill:#7c3aed,color:#fff
    style HUB fill:#ef4444,color:#fff
    style SWITCH fill:#10b981,color:#fff
    style ROUTER fill:#3b82f6,color:#fff
    style MODEM fill:#f59e0b,color:#fff
    style AP fill:#059669,color:#fff

Device	Layer	What it does
Hub	Layer 1 (Physical)	Broadcasts every signal to every port — inefficient
Switch	Layer 2 (Data Link)	Sends data only to the correct device using MAC addresses
Router	Layer 3 (Network)	Routes data between different networks using IP addresses
Modem	Layer 1	Converts digital signals to analog (for cable/DSL/fiber)
Access Point	Layer 2	Bridges wired network to wireless devices

🔢 MAC Addresses

Every network device has a MAC (Media Access Control) address — a permanent, unique identifier burned into the hardware.

Think of it like a government-issued ID number — unique to each device, never changes.

MAC Address Format: 00:1A:2B:3C:4D:5E   (6 pairs of hex digits)
                    00-1A-2B-3C-4D-5E
                    001A.2B3C.4D5E

IP vs MAC:

IP Address:  192.168.1.10  ← Like your mailing address (can change)
MAC Address: 00:1A:2B:3C:4D:5E  ← Like your fingerprint (permanent)

🔄 ARP (Address Resolution Protocol)

ARP maps IP addresses to MAC addresses so devices can talk on the local network.

sequenceDiagram
    participant Laptop as Laptop A<br/>192.168.1.10<br/>MAC: AA:AA:AA:AA:AA:AA
    participant Switch as Network Switch
    participant Printer as Printer B<br/>192.168.1.20<br/>MAC: BB:BB:BB:BB:BB:BB

    Note over Laptop,Printer: Laptop wants to send data to 192.168.1.20
    Laptop->>Switch: ARP Request: "Who has 192.168.1.20?<br/>Tell AA:AA:AA:AA:AA:AA"
    Switch->>Printer: Broadcast to all devices
    Printer-->>Laptop: ARP Reply: "192.168.1.20 is at BB:BB:BB:BB:BB:BB"
    Note over Laptop: Caches the result: 192.168.1.20 → BB:BB:BB:BB:BB:BB
    Laptop->>Printer: Now sends data directly using MAC address

Step by step:

Laptop knows the IP address (192.168.1.20) but not the MAC address
Laptop broadcasts an ARP request: “Who has this IP? Tell me your MAC!”
The device with that IP responds: “It’s me! My MAC is BB:BB:BB:BB:BB:BB”
Laptop caches the mapping (so it doesn’t ask again soon)
Now the laptop can send data directly using the MAC address

🌐 Packet Switching vs Circuit Switching

Circuit switching — A dedicated path is reserved for the entire conversation (old phone system). Packet switching — Data is split into packets, each finds its own way (the internet).

flowchart TB
    subgraph Circuit[Circuit Switching - Traditional Phone Call]
        C1["📞 Caller"] --> C2["Dedicated line reserved<br/>throughout conversation"]
        C2 --> C3["📞 Receiver"]
        C4["Even silence wastes<br/>the reserved bandwidth"]
    end

    subgraph Packet[Packet Switching - The Internet]
        P1["💻 Sender"] --> P2["Data split into packets"]
        P2 --> P3["Packet 1 → Route A"]
        P2 --> P4["Packet 2 → Route B"]
        P2 --> P5["Packet 3 → Route C"]
        P3 --> P6["💻 Receiver<br/>Reassembles packets"]
        P4 --> P6
        P5 --> P6
        P7["Efficient - bandwidth<br/>shared dynamically"]
    end

    style Circuit fill:#ef4444,color:#fff
    style Packet fill:#10b981,color:#fff

In Simple Words

Star (home WiFi), Mesh (data centers), Bus (old networks) — different ways to connect devices
Hubs broadcast to everyone; Switches send to the right device; Routers connect different networks
MAC addresses are permanent hardware IDs; IP addresses are logical addresses that can change
ARP translates IP → MAC addresses so local network communication works
The internet uses packet switching — data is split into packets that find their own way