Networking+ 1.2

Week $1$ Night $2$ Agenda

• Review: Synthesis of concepts from Week $1$ Night $1$.

• Academic Content: Chapter $1$ Part $2$ (The OSI Framework).

• Practical Application: Hands-on laboratory exercise $1.2$ using Cisco Packet Tracer.

Week $1$ Night $1$- Review

• Common Network Protocols:

  • File Transfer: FTP (File Transfer Protocol) on port $21$ and FTPS (FTP Secure) utilizing $SSL/TLS$.

  • Web Traffic: HTTP (Hypertext Transfer Protocol) on port $80$ and HTTPS (HTTP Secure) on port $443$.

  • Remote Access: RDP (Remote Desktop Protocol) for GUI access and SSH (Secure Shell) for secure command-line access.

• Network Topologies:

  • Star: All nodes connect to a central hub or switch; most common in modern LANS

  • Mesh: Every node connects to every other node (Full Mesh) or some others (Partial Mesh); provides high redundancy.

  • Bus: All nodes share a single communication line; legacy technology.

  • Hub-and-Spoke: A central 'hub' connects multiple 'spokes' (remote sites); common in $WAN$ setups.

  • Hybrid: A combination of $2$ or more different topologies to optimize performance and cost.

• Network Hardware:

  • NIC (Network Interface Card): The physical interface providing a constant connection to the network.

  • Switch: A Layer $2$ device that uses $MAC$ addresses to forward data only to the intended recipient within a $LAN$.

  • Router: A Layer $3$ device used to connect different networks and dictate the best path for data using $IP$ addresses.

• Network Types:

  • WAN: Spans large geographical areas (e.g., the Internet).

  • MAN: Connects users within a specific geographic area like a city.

  • LAN: Localized to a single room, building, or campus.

  • PAN: Very short range (e.g., Bluetooth connection between a phone and a headset).

Chapter $1$ Part $2$ Objectives

• Analyze and differentiate between the $7$ layers of the OSI model.

• Implement the standard $7$-step troubleshooting methodology for systematic problem resolution.

• Master command-line interface ($CLI$) tools for network diagnostics ($ping$, $tracert$, $ipconfig$).

The Seven-Layer OSI Model

• The OSI (Open Systems Interconnection) Model is a conceptual framework standardized by the $ISO$ to characterize the telecommunication functions of a computing system without regard to its underlying internal structure and technology. It consists of $7$ distinct layers:

  • L7: Application

  • L6: Presentation

  • L5: Session

  • L4: Transport

  • L3: Network

  • L2: Data Link

  • L1: Physical

OSI Model Overview: Encapsulation and Data Units

• Encapsulation: As data moves down from the Application to the Physical layer, each layer adds a header (and sometimes a trailer) containing control information. This is called a Protocol Data Unit (PDU).

• Decapsulation: The reverse process occurs at the receiving end, where headers are stripped as the data moves up the stack.

• PDU Names per Layer:

  • Layers 7, 6, 5: Generic Data or Payload (L7PDU).

  • Layer 4: Segment (if using TCP) or Datagram (if using UDP). Logic includes Source/Destination Port numbers.

  • Layer 3: Packet. Logic includes Source/Destination $IP$ addresses.

  • Layer 2: Frame. Infrastructure includes Source/Destination $MAC$ addresses and a FCS (Frame Check Sequence) trailer for error detection.

  • Layer 1: Bits. Raw digital signals transmitted over the media.

Detailed Explanation of OSI Layers

Layer 7: Application Layer

• Facilitates communication between software applications and lower-layer network services.

• Protocols: $DNS$ (Domain Name System), $DHCP$ (Dynamic Host Configuration Protocol), $SMTP$ (Email), and $SNMP$ (Monitoring).

Layer 6: Presentation Layer

• Acts as the 'translator' for the network. It handles data formatting, compression, and encryption/decryption (e.g., converting $EBCDIC$ to $ASCII$ or handling $SSL/TLS$ encryption).

Layer 5: Session Layer

• Establishes, manages, and terminates connections (sessions) between local and remote applications. It handles 'checkpointing' to allow data streams to resume from the last known good state if interrupted.

Layer 4: Transport Layer

• Orchestrates end-to-end communication and error recovery.

• TCP: Connection-oriented; uses a $3$-way handshake ($SYN$, $SYN-ACK$, $ACK$) to ensure reliable delivery.

• UDP: Connectionless; best-effort delivery without acknowledgement, ideal for streaming/VoIP where speed is prioritized over perfect accuracy.

• Flow Control: Prevents the sender from overwhelming the receiver with too much data at once.

Layer 3: Network Layer

• Handles logical addressing and routing. It determines the physical path the data should take based on network conditions and priority.

• IP (Internet Protocol): The primary mechanism for addressing (both $IPv4$ and $IPv6$).

• Fragmentation: If a packet is too large for a network segment's MTU (Maximum Transmission Unit), this layer breaks it down.

• ICMP: Used for diagnostic messages (e.g., 'Destination Unreachable').

Layer 2: Data Link Layer

• Manages physical addressing ($MAC$ addresses) and access to the physical media.

• Sublayers:

  • LLC (Logical Link Control): Identifies the Network layer protocol.

  • MAC (Media Access Control): Manages hardware addresses and frames.

• ARP (Address Resolution Protocol): Links an $IP$ address to a physical $MAC$ address.

Layer 1: Physical Layer

• Defines the mechanical, electrical, and functional specifications for the physical link.

• Includes connectors, cables (Cat$5e$, Cat$6$, Fiber), and signaling (voltages for copper, light pulses for fiber, radio waves for Wi-Fi).

Network Models: P2P vs. Client-Server

• Peer-to-Peer (P2P):

  • No centralized authority; every computer is an equal.

  • Pros: Inexpensive, no specialized version of $OS$ required.

  • Cons: Security is decentralized; adding more than $10$ users causes massive performance degradation.

• Client-Server:

  • Uses a central NOS (Network Operating System) like Windows Server with Active Directory.

  • Resources are stored on high-powered servers; clients 'request' services.

  • Pros: High scalability, centralized backups, and unified security policies.

  • Cons: Central point of failure; requires specialized administrative knowledge.

The $7$-Step Troubleshooting Model

1. Identify the Problem: Define symptoms. Question users carefully. Check for recent changes to the environment.

2. Establish a Theory of Probable Cause: Start with the most obvious (Layer $1$: is it plugged in?). Use top-down or bottom-up approaches.

3. Test the Theory: Prove the hypothesis. If the theory fails, return to Step $2$.

4. Establish a Plan of Action: Document steps to resolve while minimizing impact on other services.

5. Implement the Solution: Perform the fix or escalate to a senior technician.

6. Verify Full Functionality: Ensure the original problem is gone and no new problems were created. Implement preventive measures.

7. Document Findings: Create a record of the fix in a knowledge base or ticketing system to aid future troubleshooting.

• Analyze and differentiate between the $7$ layers of the OSI model.

• Implement the standard $7$-step troubleshooting methodology for systematic problem resolution.

• Master command-line interface ($CLI$) tools for network diagnostics ->$ping$ , $tracert$ , $ipconfig$).

The Seven-Layer OSI Model

• The OSI (Open Systems Interconnection) Model is a conceptual framework standardized by the $ISO$ to characterize the telecommunication functions of a computing system without regard to its underlying internal structure and technology. It consists of $7$ distinct layers:

  • L7: Application

  • L6: Presentation

  • L5: Session

  • L4: Transport

  • L3: Network

  • L2: Data Link

  • L1: Physical

OSI Model Overview: Encapsulation and Data Units

• Encapsulation: As data moves down from the Application to the Physical layer, each layer adds a header (and sometimes a trailer) containing control information. This is called a Protocol Data Unit (PDU).

• Decapsulation: The reverse process occurs at the receiving end, where headers are stripped as the data moves up the stack.

• PDU Names per Layer:

  • Layers 7, 6, 5: Generic Data or Payload (L7PDU).

  • Layer 4: Segment (if using TCP) or Datagram (if using UDP). Logic includes Source/Destination Port numbers.

  • Layer 3: Packet. Logic includes Source/Destination $IP$ addresses.

  • Layer 2: Frame. Infrastructure includes Source/Destination $MAC$ addresses and a FCS (Frame Check Sequence) trailer for error detection.

  • Layer 1: Bits. Raw digital signals transmitted over the media.

Detailed Explanation of OSI Layers

Layer 7: Application Layer

• Facilitates communication between software applications and lower-layer network services.

• Protocols: $DNS$ (Domain Name System), $DHCP$ (Dynamic Host Configuration Protocol), $SMTP$ (Email), and $SNMP$ (Monitoring).

Layer 6: Presentation Layer

• Acts as the 'translator' for the network. It handles data formatting, compression, and encryption/decryption (e.g., converting $EBCDIC$ to $ASCII$ or handling $SSL/TLS$ encryption).

Layer 5: Session Layer

• Establishes, manages, and terminates connections (sessions) between local and remote applications. It handles 'checkpointing' to allow data streams to resume from the last known good state if interrupted.

Layer 4: Transport Layer

• Orchestrates end-to-end communication and error recovery.

• TCP: Connection-oriented; uses a $3$-way handshake ($SYN$, $SYN-ACK$, $ACK$) to ensure reliable delivery.

• UDP: Connectionless; best-effort delivery without acknowledgement, ideal for streaming/VoIP where speed is prioritized over perfect accuracy.

• Flow Control: Prevents the sender from overwhelming the receiver with too much data at once.

Layer 3: Network Layer

• Handles logical addressing and routing. It determines the physical path the data should take based on network conditions and priority.

• IP (Internet Protocol): The primary mechanism for addressing (both $IPv4$ and $IPv6$).

• Fragmentation: If a packet is too large for a network segment's MTU (Maximum Transmission Unit), this layer breaks it down.

• ICMP: Used for diagnostic messages (e.g., 'Destination Unreachable').

Layer 2: Data Link Layer

• Manages physical addressing ($MAC$ addresses) and access to the physical media.

• Sublayers:

  • LLC (Logical Link Control): Identifies the Network layer protocol.

  • MAC (Media Access Control): Manages hardware addresses and frames.

• ARP (Address Resolution Protocol): Links an $IP$ address to a physical $MAC$ address.

Layer 1: Physical Layer

• Defines the mechanical, electrical, and functional specifications for the physical link.

• Includes connectors, cables (Cat$5e$, Cat$6$, Fiber), and signaling (voltages for copper, light pulses for fiber, radio waves for WiFi).

Network Models: P2P vs. Client-Server

• Peer-to-Peer (P2P):

  • No centralized authority; every computer is an equal.

  • Pros: Inexpensive, no specialized version of $OS$ required.

  • Cons: Security is decentralized; adding more than $10$ users causes massive performance degradation.

• Client-Server:

  • Uses a central NOS (Network Operating System) like Windows Server with Active Directory.

  • Resources are stored on high-powered servers; clients 'request' services.

  • Pros: High scalability, centralized backups, and unified security policies.

  • Cons: Central point of failure; requires specialized administrative knowledge.

The $7$-Step Troubleshooting Model

1. Identify the Problem: Define symptoms. Question users carefully. Check for recent changes to the environment.

2. Establish a Theory of Probable Cause: Start with the most obvious (Layer $1$: is it plugged in?). Use top-down or bottom-up approaches.

3. Test the Theory: Prove the hypothesis. If the theory fails, return to Step $2$.

4. Establish a Plan of Action: Document steps to resolve while minimizing impact on other services.

5. Implement the Solution: Perform the fix or escalate to a senior technician.

6. Verify Full Functionality: Ensure the original problem is gone and no new problems were created. Implement preventive measures.

7. Document Findings: Create a record of the fix in a knowledge base or ticketing system to aid future troubleshooting.