Jeremy's IT Lab - CCNA Course Lecture Notes

Introduction

• Free complete course for CCNA presented by Jeremy.
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• Today's focus: TCP and UDP (Layer 4 protocols).

Overview of Layer 4

• Previous layers covered: 1 (cables), 2 (MAC addresses, switching), 3 (IP addresses, routing).
• Layer 4 provides transparent data transfer between end hosts.
• It encapsulates data with a Layer 4 header and uses lower layers to deliver data unchanged.

Functions of Layer 4 Protocols

• Transparent Data Transfer: Hosts unaware of underlying network details.

• Services Provided by TCP:

  • Reliable data transfer: Ensures all data is received.
  • Error recovery: Resends data if errors occur.
  • Data sequencing: Organizes data in order.
  • Flow control: Manages data traffic to avoid overwhelming hosts.

• Layer 4 Addressing: Uses port numbers to identify application protocols and manage sessions.

• Sessions: An exchange of data between devices, allowing multiple connections simultaneously.

Port Numbers

• Well-known Ports (0-1023): Major protocols like HTTP, FTP.
• Registered Ports (1024-49151): Less strict registration for use.
• Ephemeral Ports (49152-65535): Used for random source port selection.

TCP (Transmission Control Protocol)

• Connection-oriented protocol: Establishes a connection before sending data.
• Key Features:
  • Reliable communication: Acknowledges each TCP segment.
  • Sequencing: Uses sequence numbers for proper order.
  • Flow control: Adjusts data transmission rate via window size field.

TCP Header Overview

• Key fields: Source/Destination ports, Sequence number, Acknowledgment number, Window Size.
• Flags: Important for establishing (SYN, ACK) and terminating (FIN, ACK) connections.

TCP Connection Establishment (Three-Way Handshake)

1. PC1 sends SYN to SRV1.
2. SRV1 responds with SYN-ACK.
3. PC1 sends ACK.

• TCP Connection Termination (Four-Way Handshake):
  1. PC1 sends FIN.
  2. SRV1 responds with ACK.
  3. SRV1 sends FIN.
  4. PC1 sends ACK.

TCP Reliability

• Acknowledgment and retransmission of lost segments.
• Forward Acknowledgment: Specifies the next expected segment number.
• Sliding Window: Adjusts data flow control dynamically.

UDP (User Datagram Protocol)

• Connectionless Protocol: Sends data without establishing a connection.
• Key Features:
  • No reliable communication or acknowledgments.
  • No sequencing, flow control, or error recovery.
• UDP Header: Contains four fields (Source/Destination ports, Length, Checksum).

Comparison: TCP vs. UDP

• TCP: Reliable, connection-oriented, larger overhead.
• UDP: Faster, lower overhead, no guarantees of delivery.
• Use Cases:
  • TCP: File downloads, email (SMTP).
  • UDP: Real-time applications (VoIP, video calls).

Important Protocols and Port Numbers

• TCP Protocols:

  • FTP: 20, 21
  • SSH: 22
  • Telnet: 23
  • SMTP: 25
  • HTTP: 80
  • POP3: 110
  • HTTPS: 443

• UDP Protocols:

  • DHCP: 67, 68
  • TFTP: 69
  • SNMP: 161, 162
  • Syslog: 514
  • DNS: Uses both TCP and UDP.

Review of Key Points

• Layer 4 provides services and addressing via port numbers.
• TCP is reliable and connection-oriented; UDP is simpler and faster.
• Memorization of key port numbers essential for CCNA.

Quiz Questions Overview

1. Recognize well-known port numbers (0-1023).
2. Source port range for random selections (ephemeral).
3. Features unique to TCP vs. UDP.
4. Application Layer protocols using TCP.
5. Acknowledgment values in TCP communication.

Additional Resources

• Anki flashcard deck for port numbers.
• Upcoming Wireshark demo for practical understanding.

Conclusion

• Appreciation for channel members.
• Encouragement to subscribe, like, and share.