Networking

Fundamental Concepts of Networking

  • Definition of a Network: At its core, a network links two or more computers together for the purpose of communication.

  • Methods of Connection: Computers within a network may be linked through a variety of mediums, including but not limited to:

    • Cables (Ethernet, fiber, etc.)

    • Telephone lines

    • Radio waves

    • Satellites

    • Pigeons (conceptually used in historical "IP over Avian Carriers")

    • Lasers

    • Ultrasonic audio

    • Infrared light

    • Microwave

    • Other transmission technologies.

  • Physical Realization: Dr. Hochstetler describes a network essentially as the physical interconnection of nodes, noted as "this but with computers and a lot more copper wire."

History of Networks and the Origin of the Internet

  • Birth of ARPANet (1969): The Advanced Research Projects Agency Network (ARPANET) was established as the precursor to the modern internet.

  • The Strategic Goal: The primary objective of ARPANET was to maintain open lines of communication in the event of a nuclear exchange between the United States and the USSR. By decentralizing communication, the network could survive localized destruction.

  • Legacy Influence: Reference is made to the nuclear war documentary War Games as a cultural touchstone for the era's concerns.

  • Expansion (1975): By 1975, ARPANet grew significantly, connecting diversos nodes across the globe including:

    • Pacific/West Coast: Honolulu, Hawaii (via AMES), LBL, UTAH, LLL, SAI, XEROX, TYMS, STAN, FNWS, UCLA, SDC, AFWL, USC, RAND, USC-19, GWC.

    • Central/East Coast: PURDUE, LINCOLN, MIT IPC, MIT MAC, RADO, CCA, BBN, CARNEGIE, NCC, HARVARD, RUTGERS, BELVOIR, ABERDEEN, UR PAT, SDAC, MITRE, NBS, ARPA, ETAC, RML.

    • International Nodes: Kjeller (NORSAR, Norway) and University College London (UCL).

  • Hardware of 1975 ARPANet:

    • TIP: An Interface Message Processor that can be connected to host machines and terminals.

    • IMP: An Interface Message Processor that can be connected specifically to host machines.

Evolution of Communication Models: Circuit vs. Packet-Based Networks

  • Point-to-Point Communication (Pre-ARPANet): Before the development of packet-switching, communication for both computer data and human voice was strictly point-to-point.

  • Circuit Networks:

    • These involve direct circuits established between nodes (e.g., Node A to Node B).

    • They can be mentally modeled as a "single piece of copper" connecting the computers.

    • Vulnerability: In a circuit-based environment (TL ⇌ TR, involving nodes A, B, C, and D), if a specific node such as 'B' goes offline, the circuit is broken, and communication between nodes relying on that circuit path fails.

  • Packet-Based Networks (ARPANet Innovation):

    • Developed by the Advanced Research Projects Agency of the United States Department of Defense.

    • The Packetized Standard: Messages are broken down into small units called "datagram packets."

    • Routing Logic: These packets can be individually routed through different paths to reach their destination.

    • Resilience: If node 'B' goes offline, the network can route packets through alternate nodes (e.g., routing through C or D instead) to ensure the message arrives.

    • Reassembly: Each packet is assigned a number so that the destination machine can reorder them correctly to reconstruct the original message.

    • TCP/IP Emergence: This standard eventually became Transmission Control Protocol over Internet Protocol (TCP/IP) in 1974.

Network Device Labeling and Identifiers

  • MAC (Media Access Control) Address:

    • Definition: A unique, hardcoded physical label assigned to a network interface.

    • Scope: Used for communication within a local network.

    • OSI Layer: Operates at Layer 2 (Data Link).

    • Structure: The first three octets (24 bits) are known as the Organizationally Unique Identifier (OUI), which identifies the hardware manufacturer.

    • Example: b0:de:28:90:4b:90b0:de:28:90:4b:90 (The OUI b0:de:28b0:de:28 identifies Apple, Inc.).

  • IP (Internet Protocol) Address:

    • Definition: A unique, logical label assigned to a network interface.

    • Scope: Used for communication across different, interconnected networks.

    • OSI Layer: Operates at Layer 3 (Network).

    • Example (IPv4): 192.168.0.1192.168.0.1.

  • Hostname:

    • Definition: A human-readable "label" for a device connected to a network, designed for ease of memory.

    • Example: skibidi.

  • Fully Qualified Domain Name (FQDN):

    • Definition: The complete, non-ambiguous domain name that specifies the precise location of a device or service within the domain hierarchy.

    • Example: skibidi.toilet.roblox.eu.

Network Labeling and Resolution Protocols

  • ARP (Address Resolution Protocol): Resolves or discovers the physical MAC address associated with a known IPv4 address.

    • Example: Resolving 192.168.0.1192.168.0.1 to find MAC address b0:de:28:90:4b:90b0:de:28:90:4b:90.

  • NDP (Neighbor Discovery Protocol): Performs the same function as ARP but for the IPv6 protocol.

    • Example: Resolving 2001:db8::12001:db8::1 to MAC address b0:de:28:90:4b:90b0:de:28:90:4b:90.

  • DNS (Domain Name System): Resolves or find the IP address associated with a given hostname.

    • Example: Resolving google.com to the IPv4 address 141.251.116.113141.251.116.113.

  • DHCP (Dynamic Host Configuration Protocol): Automatically assigns IP addresses and other critical network configuration parameters to devices as they connect.

    • Example: Assigning IP address 192.168.1.10192.168.1.10 to a device with MAC address 00:1A:2B:3C:4D:5E00:1A:2B:3C:4D:5E upon network joining.

The OSI Model (Open Systems Interconnection)

  • Framework Definition: A conceptual model that organizes network communication into seven distinct layers. Each layer has specific functions meant to standardize and simplify the networking process.

  • Layer 7: Application:

    • Serves as the interface for end-user applications (e.g., Google Chrome web browser, email clients).

    • Provides network services directly to software applications.

  • Layer 6: Presentation:

    • Handles data translation, encryption, and compression.

    • Ensures that the data is in a format usable by the Application layer.

  • Layer 5: Session:

    • Manages the sessions between applications.

    • Controls the dialogue, synchronization, and duration of connections.

  • Layer 4: Transport:

    • Ensures reliable data transfer across the network.

    • Manages error correction and flow control.

    • Key Protocols: TCP (Transmission Control Protocol), UDP (User Datagram Protocol).

  • Layer 3: Network:

    • Responsible for routing packets across different networks.

    • Manages logical addressing, primarily using IP addresses.

  • Layer 2: Data Link:

    • Handles physical addressing (MAC addresses) and dictates how the medium is accessed.

    • Manages error detection and correction at the hardware level.

  • Layer 1: Physical:

    • Defines the physical characteristics of the connection (cables, electrical levels, switches).

    • Transmits raw bitstreams over the physical medium.

Network and Cybersecurity Devices

Standard Network Devices

  • Switches: Devices that switch packets between specific ports. They are used to define Local Area Networks (LANs).

  • Wireless Access Points (APs/WAPs): Provide network connectivity to wireless clients.

  • Routers: Route packets between different LANs, effectively creating Wide-Area Networks (WANs).

  • Load-Balancers (LBs): Distribute incoming network traffic across multiple servers to increase service availability and reliability.

  • DNS Servers: Dedicated servers that resolve human-readable hostnames into machine-routable IP addresses.

Cybersecurity Devices

  • Firewalls (FWs): Screen traffic residing between different LANs; they are described as "sorta dumb" because they follow basic rule-based filtering.

  • Intrusion Detection Systems (IDS): Systems that monitor network traffic and log unauthorized or suspicious intrusions.

  • Intrusion Prevention Systems (IPS): An advanced version of IDS that not only monitors but actively prevents detected intrusions ("smart but angry").

  • Web Application Firewall (WAF): A firewall specifically tailored for web servers, possessing high-level logic regarding HTTP traffic ("very smart on HTTP").

The Infrastructure of the Internet

  • The Path from Local to Global:

    1. Local Environment: Your home, dorm, or local hotspot (e.g., McDonald's parking lot).

    2. Edge Devices: Devices like Tablets and Wi-Fi connect to a Router/Switch/Firewall/Gateway.

    3. ISP (Internet Service Provider): Organizations such as AT&T, Frontier, or CenturyLink.

    4. Internet Backbone: ISPs connect to Internet Exchange Points.

    5. Target Nodes: Connection terminates at a Datacenter (e.g., "FakeTube Datacenter") which houses racks of servers connected via High-speed links (e.g., 4040 Gb Ethernet).

  • Scale: The Internet is defined as the "biggest WAN on earth."