1. Cisco Network Support Certifications 2. Networking Terms 3. INTRODUCTION TO NETWORKING 4. TYPES OF NETWORK 5. The Development of the Internet 6. NETWORK ARCHITECTURE 7. TOPOLOGY 8. BUS TOPOLOGY 9. RING TOPOLOGY 10. STAR TOPOLOGY 11. MESH TOPOLOGY 12. HYBRID TOPOLOGY 13. Speed of Networking device 14. NETWORK DEVICES 15. Exploring Wireless Network 16. REPEATERS 17. HUB 18. SWITCH 19. BRIDGE 20. ROUTERS 21. TRANSMISSION Telecommunication 22. Difference between Full Duplex, Half Duplex and Simplex 23. IP-ADDRESSING and IPV4 24. IPv4 address classes 25. IPV6 [ Internet Protocol Version 6 ] 26. SPEED OF VARIOUS DEVICES 27. Network Security 28. Some basic suggestion and steps to prevent Attacks and Network security 29. OSI model 30. UPPER and LOWER Layer 31. Application Layer (Layer 7) 32. Presentation Layer (Layer 6) 33. Session Layer (Layer 5) 34. Transport Layer (Layer 4) 35. Network Layer (Layer 3) 36. Data Link Layer 2 37. Physical Layer 1 38. TCP/IP The DoD Model 39. ROUTED PROTOCOL 40. Ports and Application 41. Important Application, Protocol and Port Number 42. Router Function 43. Types of Routing Protocols 44. STARTING ROUTER 45. CISCO IOS 46. Logging in to the Router 47. CISCO Router IOS commands List 48. Setting time and date of router 49. Router configuration commands 50. Optimizing Switch and Router 51. Understanding Router Terms 52. ROUTER SECURITY 53. Configuring CISCO SWITCH Security Policy 54. IMPLEMENTING STATIC ROUTING 55. UNDERSTANDING THE NEED FOR NAT 56. WAN Connections 57. Access List [ACL] 58. VLAN [Virtual Local Area Network] 59. SPANNING TREE :- BROADCAST STORM 60. Lab 1 Setting up a Serial Interface 61. Lab 2 : IP Addressing 62. Lab 3 Static Routes 63. Lab 4 Default Routes 64. Lab 5 RIP Routes 65. Lab 6 IGRP Routes 66. Lab 7 EIGRP Routes 67. Lab 8 OSPF Routes 68. Lab 9 CHAP and RIP 69. Lab 10 Standard Access-Lists with RIP 70. Lab 11 Extended Access-Lists with RIP 71. Lab 12 Static NAT 72. Lab 13 Many to One NAT 73. Lab 14 NAT Pool 74. Lab 15 ( 2950 Trunk ) 75. Lab 16 ( 2950 Trunk Dynamic ) 76. Lab 17 (2950 VLANs) 77. Lab 18 ( 2950 Deleting VLANs ) 78. Lab 19 ( 2950 VTP ) 79. Lab 20 ( 2950 VTP w/ client ) 80. Lab 21 ( 2950 Telnet )
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Data Link Layer 2 tutorials

Data received from Network Layer 3 "Packets" is formatted into "Frames" to be transmitted to the Physical Layer 1.

  • It adds the MAC addresses to frames.

  • It performs error detection not correction.

  • The Data Link layer ensures that messages are delivered to the proper device and translates messages from the Network layer into bits for the Physical layer to transmit.

  • It formats the message into data frames and adds a customized header containing the hardware destination and source address.

  • Physical addressing or hardware addressing (rather than logical addressing) ensures that data is delivered to the appropriate node on the LAN.

  • This layer is also responsible for error notification (not correction), network topology, and flow control.

  • Two devices that are used at Data Link Layer 2 are Bridges and Switch.

  • Two domains determine data transport reliability:

1) Broadcast Domain: A group of nodes that can receive each otherís broadcast messages and are segmented by routers.

2) Collision Domain: A group of nodes that share the same media and are segmented by switches. A collision occurs if two nodes attempt a simultaneous transmission. Carrier Sense Multiple Access Collision Detection (CSMA/CD) is an access method that sends a jam signal to notify the devices that there has been a collision. The devices then halt transmission for a random back-off time.

  • This is the only layer of the OSI model that has sublayers. The two sublayers define the IEEE Ethernet 802.3 frame, which in turn provides physical addressing and flow control. Routed protocol information IP, IPX, AppleTalk, and so on is provided to the upper layers.


The IEEE Ethernet 802.3 sublayers are

1) Media Access Control (MAC) and

2) Logical Link Control (LLC).


MAC (Media Access Control)

  • The MAC address is the hard-coded unique address on the network interface controller (NIC) LAN Card.

  • Each MAC address must be unique and it is in following format

  • It consist of 48 bits.

  • It must be displayed by 12 hexadecimal number from (0 to 9 and A to F).

  • The first 6 hexadecimal digits in address are reserved for Vendor code or Manufacture unique identifier and it is assigned by NIC manufacturer.


LLC (Logical Link Control)

  • The LLC sublayer complements the MAC sublayer in the ethernet model; the LLC is responsible for framing, error, and flow control.

  • LLC provides a service access point (SAP) identifier in the frame.

  • The SAP field of the frame consists of one byte that identifies an upper layer protocol (for example, 06 = IP, whereas E0 = IPX). The LLC inserts a destination SAP (DSAP) and a Source SAP (SSAP) in the frame.

  • Following chart shows example of Ethernet frame.

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