Networking Refresher

Introduction

• IP Addresses

• MAC Addresses

• TCP, UDP, and the Three-Way Handshake

• Common Ports and Protocols

• The OSI Model

• Subnetting

IP Addresses

Layer 3 - Network

IP (Internet Protocol) addresses, IPv4 and IPv6 - core internet addressing protocols, operating on layer 3 of OSI model.

• IPv4: 192.168.0.1 - decimal notation

  • 4 octets of 8 bits = 32 bits

  • Total IPv4 addresses:

• IPv6: 2001:0db8:85a3:0000:0000:8a2e:0370:7334 - hexadecimal notation

  • 8 groups of 16 bits = 128 bits

  • Total IPv6 addresses:

Key IPv6 improvements:

• Enhanced security

• Simplified network configuration

• More efficient routing

Transition challenges:

• IPv4 and IPv6 not directly compatible

• Ongoing global shift from IPv4 to IPv6

• Critical for sustaining internet growth and accommodating future devices

Displays the network interface configuration and status:

ifconfig

ipconfig

MAC Addresses

Layer 2 - Data Link

MAC (Media Access Control) address - unique identifier assigned to network interface controllers (NICs) of network devices.

• MAC Address: 00:1A:2B:3C:4D:5E - hexadecimal notation

  • 6 pairs of hexadecimal digits = 48 bits:

    • First 3 pairs: Manufacturer identifier

    • Last 3 pairs: Unique device identifier

Lookup devices using the first 3 pairs: https://www.macvendorlookup.com

TCP, UDP, and the Three-Way Handshake

Layer 4 - Transport

TCP (Transmission Control Protocol) and UPD (User Datagram Protocol) - transport layer protocols in computer networks.

• TCP:

  • Connection-oriented

  • Reliable, ordered, error-checked delivery

  • Uses acknowledgment, retransmission, and flow control

  • Breaks data into packets with sequence numbers

  • Suitable for: web browsing, email, file transfer, remote login

• UDP:

  • Connectionless

  • Simpler and lightweight

  • No guaranteed delivery or packet order

  • Suitable for: streaming media, online gaming, DNS, VoIP

Three-Way Handshake - establishes TCP connections:

1. SYN: Client sends SYN packet with initial sequence number

2. SYN-ACK: Server responds with SYN-ACK packet, own sequence number

3. ACK: Client acknowledges with ACK packet, incremented sequence number

Capture Packet Data using Wireshark:

wireshark&

Common Ports and Protocols

TCP Protocols:

UDP Protocols:

Protocols using both TCP and UDP:

The OSI Model

OSI (Open Systems Interconnection) model - conceptual framework standardizing communication system functions into seven distinct layers.

key aspects:

• Separates complex network communication into manageable layers

• Facilitates interoperability and troubleshooting

• Conceptual model, not always reflecting exact implementations

• Useful reference for understanding network communication

Subnetting

Subnetting - Process of dividing a network into smaller subnetworks

CIDR (Classless Inter-Domain Routing) - Method to represent IP addresses and subnet masks

Concepts:

• Borrows bits from host portion to create subnet identifier

• Allows efficient use of IP addresses

• Facilitates network management and routing

CIDR Notation:

• Format: IP address/prefix length

• Example: 192.168.0.0/24

  • First 24 bits: Network portion

  • Remaining 8 bits: Host portion

Subnetting example:

Subnetting (borrowing 2 bits):

New Subnet Mask: 255.255.255.192

Benefits:

• Flexible network boundaries

• Efficient address allocation

• Enhanced network organization

Subnetting Sheet:

Bits Sheet:

How to calculate the Subnet: