Networking

Key Networking Concepts

Understanding the roles of various protocols and port ranges is essential for effective networking. Below is an overview of critical concepts:

TCP and UDP Protocols

• Encapsulation: Both TCP and UDP are encapsulated within the IP protocol, enabling communication over networks.
• OSI Layer: Operate at OSI Layer 4 (Transport Layer), managing data delivery between applications.

TCP (Transmission Control Protocol)

• Connection-oriented: Ensures reliable data transfer through acknowledgment and retransmission.
• Flow Control: Manages data flow to prevent overwhelming the receiver.
• Use Cases: Web browsing (HTTP/HTTPS), email (SMTP, IMAP), file transfers (FTP).

UDP (User Datagram Protocol)

• Connectionless: Sends data without establishing a connection, trading reliability for speed.
• No Flow Control: Suitable for time-sensitive transmissions.
• Use Cases: Streaming (audio/video), DNS queries, VoIP.

Port Ranges

• Non-Ephemeral Ports (0–1023):

  • Also known as well-known ports, used for standardized services.
  • Examples:
    • HTTP (80)
    • HTTPS (443)
    • FTP (21)

• Ephemeral Ports (1024–65535):

  • Temporary ports assigned dynamically for client-side communication.

ICMP (Internet Control Message Protocol)

• Purpose: Used for network diagnostic and administrative tasks rather than data transfer.
• Functions:
  • Ping requests to check host availability.
  • Traceroute for path analysis.

The OSI Model

The OSI (Open Systems Interconnection Reference) Model is used as a reference for understanding how network communication occurs. Each layer has specific responsibilities and includes certain technologies or protocols.

Layer 1 - Physical Layer

• Description: Handles the physical connection between devices, including transmission of raw binary data over physical mediums.
• Typical Components:
  • Cables (Ethernet, fiber optics, coaxial)
  • Connectors (RJ45, RJ11)
  • Physical network devices (hubs, repeaters)
  • Transmission standards (voltage levels, timing)

Layer 2 - Data Link Layer

• Description: Provides reliable data transfer by addressing and error detection between directly connected nodes.
• Typical Components:
  • MAC (Media Access Control) addresses
  • Switches
  • Ethernet (IEEE 802.3), Wi-Fi (IEEE 802.11)
  • Frame structure and error-checking mechanisms (e.g., CRC)

Layer 3 - Network Layer

• Description: Handles logical addressing and routing of data packets across networks.
• Typical Components:
  • IP addresses (IPv4, IPv6)
  • Routers
  • Protocols (e.g., IP, ICMP, ARP)
  • Packets and packet forwarding

Layer 4 - Transport Layer

• Description: Ensures end-to-end communication, error recovery, and flow control between devices.
• Typical Components:
  • TCP (Transmission Control Protocol) segments
  • UDP (User Datagram Protocol) datagrams
  • Port numbers
  • Flow control, error detection, and retransmission mechanisms

Layer 5 - Session Layer

• Description: Manages and maintains communication sessions between applications.
• Typical Components:
  • Session establishment, management, and termination
  • Protocols (e.g., NetBIOS, RPC, PPTP)
  • Checkpoints for data recovery in case of interruptions

Layer 6 - Presentation Layer

• Description: Translates, formats, and secures data for the application layer.
• Typical Components:
  • Data encoding (e.g., ASCII, EBCDIC)
  • Data compression (e.g., JPEG, GIF)
  • Application encryption and decryption (e.g., SSL/TLS, HTTPS)

Layer 7 - Application Layer

• Description: Provides an interface for end-user applications to communicate over a network.
• Typical Components:
  • Web browsers and servers
  • Protocols (e.g., HTTP, FTP, SMTP, DNS)
  • APIs for network services (e.g., REST, SOAP)
  • User-facing applications (e.g., email clients, chat applications)

Routing & Switching

This guide covers essential concepts in routing and switching, including MAC addresses, duplex modes, casting types, and routing protocols.

MAC (Media Access Control)

• Description: The hardware address of a network adapter.
• Characteristics:
  • Unique and 6 bytes long.
  • Used for communication within a local network.

Duplex Modes

• Half-Duplex:

  • Devices can either send or receive data but not both simultaneously.
  • Example: Legacy Ethernet hubs.

• Full-Duplex:

  • Devices can send and receive data simultaneously.
  • Example: Modern Ethernet switches.

Collisions and CSMA

• Collision: Occurs when two devices try to communicate simultaneously.
• CSMA/CD (Carrier Sense Multiple Access/Collision Detect):
  • Used in half-duplex Ethernet to manage collisions.
• CSMA/CA (Collision Avoidance):
  • Prevents collisions; often used in wireless networks where collision detection is impractical.

Switches

• Functions:
  • Forwards or drops frames based on MAC address.
  • Maintains a MAC address table.
  • Ensures a loop-free environment using STP (Spanning Tree Protocol).
• Features:
  • Broadcast Frames: Sent to all devices (e.g., ARP requests). Stops at routers.
  • ARP (Address Resolution Protocol): Maps IP addresses to MAC addresses.

Casting Types

• Unicast:
  • Communication between one sender and one receiver.
  • Example: Web surfing, file transfers.
• Broadcast:
  • Sends information to all devices in the broadcast domain.
  • Limited to IPv4; not used in IPv6.
• Multicast:
  • Sends information to a specific group of devices.
  • Example: Multimedia delivery.

Protocol Data Unit (PDU)

• Definition: A unit of data for transmission.
• Examples by OSI Layer:
  • Ethernet: Frame
  • IP: Packet
  • TCP: Segment
  • UDP: Datagram

Maximum Transmission Unit (MTU)

• Definition: The largest IP packet size that can be sent without fragmentation.
• Impact: Fragmentation slows data transfer.

STP and RSTP

• STP (Spanning Tree Protocol): Prevents loops in a network.
  • Port States:
    • Blocking: Prevents loops.
    • Listening: Cleans the MAC table.
    • Learning: Adds MAC addresses to the table.
    • Forwarding: Operational state for data transmission.
    • Disabled: Port is turned off by admin.
• RSTP (Rapid Spanning Tree Protocol, 802.1w):
  • Faster convergence than STP.
  • Backwards-compatible.

Additional Networking Features

• Trunking: Connects multiple VLANs over a single link.
• DMZ (Demilitarized Zone): Adds an extra layer of security for sensitive services.
• Port Mirroring: Copies traffic for analysis (e.g., SPAN port).

Routers

• Function: Directs IP packets based on destination IP addresses.
• Routing Types:
  • Static Routing:
    • Manually configured by admins.
    • Secure but lacks automatic rerouting.
  • Dynamic Routing:
    • Routers exchange routing information.
    • Scalable and automatic but requires more resources.
  • Default Route:
    • Used when no specific route is available.

Routing Protocols

• Interior Gateway Protocol (IGP):
  • Used within a single AS (Autonomous System).
  • Examples: OSPF, RIPv2 (IPv4), OSPFv3, RIPng (IPv6).
• Exterior Gateway Protocol (EGP):
  • Routes between multiple AS.
  • Example: BGP (Border Gateway Protocol).
• Dynamic Protocol Types:
  • Distance-Vector: Uses hop count (e.g., RIPv2, EIGRP).
  • Link-State: Considers connectivity and speed (e.g., OSPF).
  • Hybrid: Combines features of both (e.g., BGP).

IP Addressing

• IPv4:
  • Length: 4 bytes (32 bits).
  • Format: Four octets separated by dots.
• IPv6:
  • Length: 16 bytes (128 bits).
  • Format: Eight groups of hexadecimal values.
• Other Features:
  • Dual-stack: Supports both IPv4 and IPv6 simultaneously.
  • Tunneling: Allows IPv6 traffic over IPv4 networks.

Quality of Service (QoS)

• Purpose: Manages and prioritizes network traffic.
• Methods:
  • CoS (Class of Service).
  • DiffServ (Differentiated Services).

Advanced Concepts

• Port Forwarding: Maps external IP/port to internal IP/port; also called static NAT.
• Access Control Lists (ACLs):
  • Filters traffic based on rules.
  • Often used in firewalls with an implicit deny rule.
• Circuit Switching: Establishes a dedicated connection (e.g., PSTN, ISDN).
• Packet Switching: Data is divided into packets and sent over shared media (e.g., SONET, ATM, DSL).
• Software Defined Networking (SDN):
  • Separates control and data planes.
  • Centralized and programmable management.