Notes for Computer Networks Lab 01

Lab Rules and Session Expectations

• Maintain discipline during the lab.
• Listen and follow the instructions as they are given.
• Just raise hand if you have any problem.
• Completing all tasks of each lab is compulsory.
• Get your lab checked at the end of the session.

What is a Network

• Network (A group or system of interconnected people or things).
• Computer Network: a telecommunications network which allows nodes to share resources.
• In computer networks, networked computing devices exchange data with each other using a data link.
• Connections between nodes are established using either cable media or wireless media.
• Types of Computer Network based on size include: LAN, MAN, WAN.

Host and Topology

• Host: A device (e.g., computer or server) connected to a network that communicates within the network.
• Each host typically has a unique identifier, like an IP address, to enable data exchange.
• Topology: The arrangement of links, nodes, etc., in a network. It can be depicted physically or logically.
• Common LAN topologies: bus, ring, star, tree, and mesh.

RJ45 Connector and Wiring Schemes

• RJ45 Connector: An 8-pin/8-position plug or jack used to connect computers onto Ethernet-based LANs.
• Two wiring schemes used to terminate twisted-pair cable onto the connector interface: T568A and T568B.
• These schemes define the color order of wires on the connector.

Types of Cables

1) Straight Cable

• Used to connect different types of devices.
• Common uses include:
  • Connect a computer to a switch/hub's normal port.
  • Connect a computer to a cable/DSL modem's LAN port.
  • Connect a router's WAN port to a cable/DSL modem's LAN port.
  • Connect a router's LAN port to a switch/hub's uplink port (for expanding the network).
  • Connect 2 switches/hubs using an uplink port on one and a normal port on the other.
• Visual identifier: Both sides of the cable have the same wire arrangement/colors.

2) Crossover Cable

• Used to connect same-type devices directly or for certain expansion scenarios.
• Common uses include:
  • Connect 2 computers directly.
  • Connect a router's LAN port to a switch/hub's normal port (normally used for expanding network).
  • Connect 2 switches/hubs using normal ports on both switches/hubs.
• Visual identifier: The wire arrangement on Side A and Side B are different in color sequence.

Auto-MDI/MDI-X

• If there is auto MDI/MDI-X support on a switch, hub, network card, or other devices, you may not need a crossover cable.
• The crossover function can be enabled automatically when needed.

Network Terminologies

• NIC (Network Interface Card): The hardware interface from a host to the network.
• MAC (Media Access Control): The physical address of a device. Example: $00:C0:9F:9B:D5:46$.
• Hub: A basic device that connects multiple devices but has no routing tables or intelligence; data is broadcast to all ports.
• Switch: Connects devices on a network using packet switching to receive, process, and forward data to the destination.
• Router: Decides where a packet should be sent to reach a destination outside the local network.
• IP Address: Addresses consisting of four decimal numbers. Examples: $192.168.0.1$ and $131.170.40.33$.
• Port Address: Each host has $65{,}535$ ports, each mapped to a specific application capable of sending/receiving packets.
• Gateway Address: The address of the router that connects a network to other networks and the Internet.
• Domain Name: Human-readable names that map to IP addresses (e.g., $www.google.com$ maps to $66.102.7.104$).
• DNS Server: Domain Name System Server; converts between IP addresses and domain names.
• DHCP: Dynamic Host Configuration Protocol; can assign a unique IP address to a host upon restart and provide a DNS address.

OSI Model (Overview)

• OSI model is a concept-based model that defines and standardizes how a computing or telecommunication system functions.
• Goal: Achieve interoperability through standards among diverse communications.
• It is a Layer-Based System with seven distinct layers.
• The names of the seven layers are not listed in the provided content.

Operating Systems: Windows & Linux Commands

• Most computers run Linux or Windows.
• Linux (overview):
  • Free and open source.
  • Open source reduces likelihood of hidden security weaknesses.
  • Forms the basis of many networking devices (e.g., routers).
  • Provides a powerful command line for scripting and network exploration.
  • Use manual pages (e.g., {
    }man ping) or info pages (e.g., {
    }info ping).
  • Some commands require root privileges; you may log in as a user and open a root terminal.
• Windows (overview):
  • Dominates the desktop market; GUI is user-friendly for many.
  • Windows also provides command line programs and GUI tools for network configuration.
  • To explore command options, you can type: {
    }hh ntcmds.chm in the terminal, and for command-specific help use: $-h, /?, -help, or ?$
• Note: Every engineer with networking knowledge should be familiar with both OSs.

Common Linux Commands

• Ifconfig
• hostname
• nslookup
• ping
• traceroute
• netstat
• Usage notes:
  • To find the IP address of the computer/host: $ifconfig$
  • To display the hostname: $hostname$
  • To list info about DNS and joined hosts: $nslookup$
  • To check if a host is reachable (by IP or hostname): $ping$
  • To trace route from a host through internet routers: $traceroute$
  • To print status of network ports, routing tables, and more: $netstat$

Common Windows Commands

• ipconfig
• hostname
• nslookup
• ping
• tracert
• Netstat
• Usage notes:
  • To view network configuration and IP details: $ipconfig$
  • To display the hostname: $hostname$
  • To query DNS information: $nslookup$
  • To check connectivity: $ping$
  • To trace route to a destination: $tracert$
  • To view network ports and routing information: $netstat$

IP Addressing and Subnets (IPv4)

• An IP address is a categorical division of internet protocol addresses used for IPv4-based routing. Classes are used for different types of networks.
• In some networks behind a router, addresses belong to default public/private subnets associated with classes A, B, or C.
• Subnet Mask (default unsubnetted classes):
  • For Class A: 1s for network/subnet bits and 0s for host bits. Example: $255.0.0.0 = 11111111.00000000.00000000.00000000$
  • For Class B: $255.255.0.0 = 11111111.11111111.00000000.00000000$
  • For Class C: $255.255.255.0 = 11111111.11111111.11111111.00000000$
• Note: The description mentions that the default, unsubnetted network has 1s for network/subnet bits and 0s for host bits; the subnetting details were not further elaborated beyond these examples.

IP Addressing Examples and Class Concepts

• IP address examples provided: $192.168.0.1$ and $131.170.40.33$.
• A host or router requires an IP address to participate in data exchange within a network.

Summary of Key Points

• Networks enable resource sharing across connected devices via wired or wireless media.
• Local, metropolitan, and wide-area networks are categorized by scale (LAN/MAN/WAN).
• Topologies describe how devices are interconnected; common LAN topologies include bus, ring, star, tree, and mesh.
• RJ45 connectors and wiring schemes (T568A/B) define pinouts for Ethernet cables on LANs.
• Straight cables connect different device types; crossover cables connect similar device types; auto-MDI/MDI-X can automate cross-over behavior.
• Core network devices include NIC, MAC, Hub, Switch, Router, and Addressing concepts (IP, Port, Gateway).
• DNS and DHCP provide name resolution and dynamic IP assignment respectively.
• The OSI model provides a framework of seven layers to standardize network communications, emphasizing interoperability.
• Linux and Windows offer complementary command ecosystems for network diagnostics and configuration.
• IP addressing in IPv4 uses classes (A, B, C) with default subnet masks; subnet masks define which bits represent the network vs. host portions.