Computer Network is an interconnection of multiple devices using multiple paths for the purpose of sending/receiving data or media. Multiple devices/mediums (e.g., routers, switches, hubs, and bridges and protocol rules are used to support the communication.

Key Concepts:

  • Network – Computers or devices connected in some way to exchange data.
  • Types of area networks – Local (LAN), Metropolitan (MAN) and Wide (WAN) area networks.
  • Network Topology: Physical Layer connections (e.g., Bus, Star, Mesh, Ring, and Daisy chain)
  • Network Protocols: set of rules or algorithms for communicating across the network
    • OSI Framework – Protocol reference model that specifies 7 layers of standards for communications
    • TCP/IP – Internet protocol suite standards used in computer networks (e.g., TCP, IP, UDP, ARP, DHCP, FTP, etc.).
  • Network Data Units: Packaging formats for data transmission at different layers (e.g., bits, frames, packets, segments, data)
  • Network Addresses:
    • Domain Name –  Assigned text label that identifies specific a Internet Protocol resource (i.e.,
    • Sub Domain – part of a larger domain used to improve efficiency or control (i.e.,
    • IP Address: Numeric address string assigned to devices across the network ; Consists of 4 bytes separated by periods (e.g.,
      • IPv4 address is 32-bits
      • IPv6 address is 128-bits.
    • MAC Address : physical address assigned by the manufacturer and is associated with its NIC (Network Interface Card). Type “ipconfig/all” .
    • Network Port: logical channel used to send/receive data on a device (range of 0-65535 addresses with 216 ports available). (Type “netstat -a” )
    • Network Socket: The unique combination of IP address and Port number that serves as an endpoint for sending and receiving data.
    • Host name: associated with a unique device name known as Hostname. (type ‘hostname’)
  • Address Servers:
    • DNS Server: Domain Name system translates web addresses (URLs) into their corresponding IP addresses. (use ‘nslookup’)
    • DCHP Server: Dynamically assigned an IP address when a device connects to the network
  • Other Network Concepts:
    • Software defined Networking (SDN)
    • Virtual LAN (VLAN) – any broadcast domain that is partitioned and isolated in a computer network at the data link layer (OSI layer 2).
    • Wireless (Wi-Fi) – wireless network protocols, based on the IEEE 802.11 family of standards, allowing nearby digital devices to exchange data by radio waves.
    • Internet – global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate.

OSI Model:

The Open Systems Interconnection model (OSI model) standardizes the interoperability of diverse systems by using standard interface protocols (rules). The model partitions a communication connections into the following (7) OSI Layers.

TCP IP Model:

Network Addresseses

  • MAC Address – Media Access Control Address is unique physical address of computer. Factory assigned in the NIC card for Layer2 Address Resolution Protocol (ARP). Six (6) bytes (48 bits) long.
  • IP address – logical identifier of a network connection for a device. Network assigned for Layer3. Four (4) bytes (32 bits)
  • Network Address Translation (NAT) – Private IP address or local address are translated into the public IP address. 
  • Port Address Translation (PAT) – Private IP addresses are translated into the public IP address via Port numbers.

Network Ports

A port number is used to connect to a Internet Protocol (IP) server and can be anything from 0 to 65535. The two common types of ports are TCP (Transmission Control Protocol) and UDP (User Datagram Protocol). Below are a few common ports to know by heart:


Network Traffic Analysis files 

  • Network Packets – formatted unit of data carried by a packet-switched network. A packet consists of control information and user data;[1] the latter is also known as the payload. 
  • Pcap – Packet Capture File which includes: (1) Source and Destination port #s , (2) IP addresses , (3) Physical (MAC) addresses, (4) Protocol and Encryption info, (5) Header and Payload info, (6) Wireless info and other data.  Use Wireshark or equivalent tool to analyze the PCAP. 

Network commands

  • ping – Linux (and Windows) command to measure the round-trip time for messages sent to a destination computer that are echoed back to the source. (e.g. ping
  • Nmap – Discover hosts and services on a computer network by sending packets and analyzing the responses.
  • traceroute – Linux command to measuring transit delays of packets across an Internet Protocol (IP) network
  • netstat – a command-line utility that displays TCP connections (both incoming and outgoing), routing tables, network interface, and network protocol statistics (e.g., netstat -r, netstat -a, netstat -ie, etc.)
  • ifconfig –  command utility for displaying the network interface configuration. (e.g., ifconfig -a)
  • host – When used with a fully qualified domain name (FQDN) the host command will return information associated with that name such as its IP address (e.g.  host