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Comptia Security + Chapter 1 501
- 1. CompTIA Network + Chapter 2 Dissecting the OSI Model
- 2. Objectives What is the purpose of a Network model? What are the layers of the OSI model? What are the characteristics of each layer of the OSI model? How does the TCP/IP stack compare to the OSI model? What are the well-known TCP and/or UDP port numbers for a given collection of common applications
- 3. The Purpose of Reference Models It breaks network communication into smaller, simpler parts that are easier to develop. It facilitates standardization of network components to allow multiple-vendor development and support. It allows different types of network hardware and software to communicate with each other. It prevents changes in one layer from affecting the other layers so that they can develop more quickly. It breaks network communication into smaller parts to make learning it easier to understand.
- 4. Warriors of the Net
- 5. The OSI seven-layer model Application Presentation Session Transport Network Data Link Physical Figure 2-2 OSI Stack 1 2 3 4 5 6 7
- 6. Mnemonics for the OSI Model Away Pizza Sausage Throw Not Do Please All People Seem To Need Data Processing
- 7. Protocol Data Unit (PDU) Application Presentation Session Transport Network Data Link Physical Segments Packets Frames Bits Figure 2-3 PDU Names
- 8. Quick Summary of Layers 1-4 Transport Network Data Link Physical 1 2 3 4 TCP & UDP Ports Routers, IP Address Switches, MAC Address Cables Service WAN LAN
- 9. OSI Layers in Wireshark 1 2 3 4 7
- 10. Physical Layer Application Presentation Session Transport Network Data Link Physical How Bits are represented on the medium Wring standards for connectors and jacks Physical topology Synchronizing bits Bandwidth usage Multiplexing strategy Figure 2-4 Layer 1: Physical Layer
- 11. Wiring Standards
- 12. Asynchronous and Synchronous Communications Synchronizing Bits Two devices must agree on when one bit stops and another bit starts Asynchronous Uses start and stop bits Synchronous Internal clocks are synchronized at each end of the cable
- 13. Bandwidth Usage Broadband Multiple channels share the same medium Ex: cable TV uses frequency division multiplexing (each channel uses a different frequency range) Baseband The whole medium is used for one transmission Example: Ethernet
- 14. ABCA_CABCA_C Time-Division Multiplexing (TDM) Each channel gets the same amount of time on the wire AAAA B_B_ CCCC
- 15. ABCACABCAC Statistical Time-Division Multiplexing (StatTDM) AAAA B_B_ CCCC Busy channels get more time on the wire
- 16. Frequency Division Multiplexing (FDM) AAAA B_B_ CCCC Example: signals sent with different colors through the same fiber optic cable AAAA B_B_ CCCC AAAA B_B_
- 17. Layer 1 Devices Cables Wireless access points Hubs Because they dont pay any attention to addresses, they just deliver signals to every connected device like a crossover cable
- 18. Data Link Layer Data Link Application Presentation Session Transport Network Physical Physical Addressing Logical topology Method of transmitting on the media Figure 2-8 Layer 2: The Data Link Layer MAC LLC Connection Services Synchronizing transmissions
- 19. MAC Addresses IPCONFIG /ALL Physical Address Built into the network interface
- 20. Connection Services Flow control Prevents sender from sending data faster than the client can accept it Error control When a frame is received, a checksum is used to detect errors Usually a Cyclic Redundancy Check (CRC) If the receiver's checksum does not match the sender's checksum, the frame is discarded and resent
- 21. Layer 2 Devices Switches Bridges Network Interface Cards (NICs)
- 22. Network Layer Network Data Link Application Presentation Session Transport Physical Logical addressing Switching Route discovery and selection Connection services Bandwidth usage Multiplexing strategy Figure 2-9 Layer 3: The Network Layer
- 23. IP Address Logical address Changes when the device is moved
- 24. Switching Packet switching Data is broken into packets Many packets travel along network connections like cars on a freeway Circuit switching A physical line is dedicated to each connection Ex: old copper landline phone systems Message switching Store-and-forward, like email
- 25. Layer 3 Devices Routers Multilayer Switches
- 26. Transport Layer Transport Network Data Link Application Presentation Session Physical TCP/UDP Windowing Buffering Figure 2-10 Layer 4: The Transport Layer
- 27. TCP and UDP Transmission Control Protocol (TCP) Connection-oriented and reliable Handshake makes sure both ends are ready Segments are acknowledged and resent if necessary User Datagram Protocol (UDP) Connectionless and unreliable No handshake Best-effort delivery, no acknowledgements
- 28. TCP Sliding Window Sender Receiver Window Size 1 Segment 1 Ack 2 Window Size 2 Ack 4 Segment 2 Segment 3 Window Size 4 Ack 8 Segment 4 Segment 5 Segment 6 Segment 7 Figure 2-11 TCP Sliding Window
- 29. ICMP (Internet Control Message Protocol) At layer 4 Used by ping and traceroute, and to indicate errors such as dropped packets
- 30. Session Layer Session Transport Network Data Link Application Presentation Physical Setting up a session Maintaining a session Tearing down a session Figure 2-12 Layer 5: The Session Layer
- 31. Example of a Session User logs in with a username & password All data now has a special significance until that user logs off, or the session times out, or is terminated some other way Layer 6 Protocol H.323 (voice or video) NetBIOS (file sharing)
- 32. Presentation Layer Presentation Session Transport Network Data Link Application Physical Data formatting Encryption Figure 2-13 Layer 6: The Presentation Layer
- 33. Application Layer Application Presentation Session Transport Network Data Link Physical Application services Service advertisement
- 34. Application Layer Closest to the user Hands data to an application in the format it expects, with no addresses or other transmission artifacts Examples: a downloaded file, an email message
- 35. The TCP/IP Stack Application Transport Internet Network Interface
- 36. The TCP/IP and OSI Models Compared Application Transport Internet Network Interface TCP/IP Stack Application Presentation Session Transport Network Data Link Physical OSI Stack Figure 2-15 TCP/IP Stack
- 37. IP Ver4 Header
- 38. TTL (Time-to-Live) TTL decreases by one each time the packet is forwarded by a router If TTL reaches zero, the packet is discarded This eliminates packets trapped in routing loops
- 40. TCP Header Figure 2-17 TCP Segment Format
- 41. TCP Header Fields Port numbers Indicate which program on the end device should receive the data Examples: Port 25 for email, 80 for HTTP Window size Number of bytes that can be sent before waiting for an ACK
- 42. TCP Header Fields Sequence and Acknowledgement numbers Used to put packets in order to reassemble files and other large messages Flags like SYN and ACK are used for the TCP handshake and to acknowledge data received
- 43. UDP Header 0 16 31 SOURCE PORT DESTINATION PORT LENGTH CHECKSUM No handshake, acknowledgements, sequencing, or flow control
- 44. Common Ports Link Ch 2d for flash cards
- 45. Port Types Port numbers are assigned in various ways, based on three ranges: System Ports (0-1023), System Ports are assigned by IETF process for standards-track protocols, as per RFC6335. Also known as well- known-ports User Ports (1024-49151) ,User Ports are assigned by IANA using the "Expert Review" process, as per RFC6335 Dynamic and/or Private Ports (49152-65535), Dynamic Ports are not assigned, they are dynamically created as your computer need them. Also known as ephemeral ports.
- 46. Communication Between Two Systems