Data_Link_Layer_OSI_Model summary type.pptx

basic summary

1. Data Link Layer – Cisco Networking Class Understanding OSI Layer 2: Functions, Protocols, and Applications

2. Learning Objectives Explain the role of the Data Link Layer in the OSI Model Describe framing, addressing, error detection, and access control Identify Layer 2 devices and protocols Apply concepts in troubleshooting scenarios

3. OSI Model Review Layer 1 – Physical Layer 2 – Data Link (focus of this session) Layer 3 – Network Layer 4 – Transport Layers 5-7 – Session, Presentation, Application

4. Definition Provides reliable data transfer across physical link Encapsulates raw bits into frames Ensures error detection and access control

5. Responsibilities Framing – organizes bits into frames Addressing – MAC addresses for identification Error Detection – CRC, checksum Flow Control – manages transmission rate Access Control – regulates access to medium

6. Layer 2 Devices Network Interface Card (NIC) Switches – forward frames based on MAC Bridges – connect LAN segments

7. Frame Structure Header – contains addressing information Payload – encapsulated data Trailer – error detection (CRC)

8. MAC Addressing 48-bit physical address Format: 00:1A:2B:3C:4D:5E OUI (first 24 bits) = vendor Last 24 bits = unique device ID

9. Types of Communication Unicast – one-to-one Broadcast – one-to-all Multicast – one-to-many (group)

10. LLC & MAC Sublayers LLC – Logical Link Control Identifies upper-layer protocols (IP, IPX, etc.) MAC – Media Access Control Controls frame access to the medium

11. Media Access Methods CSMA/CD – Ethernet, detects collisions CSMA/CA – Wi-Fi, avoids collisions Token Passing – legacy LANs

12. Switching Basics Switches learn MAC addresses from incoming frames Build MAC address table dynamically Forward frames only to intended port

13. VLANs Virtual LANs segment broadcast domains 802.1Q tagging used to separate traffic Improves security and performance

14. Error Detection Causes: noise, collisions, interference CRC – Cyclic Redundancy Check Checksum, Parity bits

15. CRC Example Data: 1101011011 Divisor (Generator): 10011 Division remainder = 1110 Frame sent = 11010110111110

16. ARQ Protocols Stop-and-Wait ARQ Go-Back-N ARQ Selective Repeat ARQ

17. IEEE 802 Standards 802.3 – Ethernet 802.11 – Wi-Fi 802.5 – Token Ring (legacy)

18. PPP and HDLC Point-to-Point Protocol (PPP) High-Level Data Link Control (HDLC) Used in WAN links

19. ARP (Address Resolution Protocol) Maps IP address to MAC address Essential for local communication ARP cache stores resolved addresses

20. Troubleshooting at Layer 2 Duplex mismatches MAC flapping issues Spanning Tree Protocol (STP) loops

21. Wireshark Example Capture Ethernet II frame Fields: Destination MAC, Source MAC, EtherType Inspect CRC in trailer

22. Summary Data Link Layer provides reliable local delivery Uses MAC addressing and framing Detects errors with CRC Supports LAN/WAN protocols and VLANs

23. Quiz Questions 1. Which sublayer handles error detection? 2. What is the size of a MAC address? 3. Which IEEE standard defines Wi-Fi? 4. What is the purpose of VLAN tagging?

24. Case Study Small LAN topology with switches and hosts Frame forwarding based on MAC addresses Troubleshooting misconfigured VLAN

25. Q&A Questions? Discussion and clarifications