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Ccna introduction
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1- CCNA - Introduction

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CCNA - Introduction

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1- CCNA - Introduction

  1. 1. CCNA – INTRODUCTION By: Sameh El-Hakim Cyber Security Engineer
  2. 2. INTRODUCTION Network is a group of devices connected together with certain topology or wireless. Topologies types:  Bus  Ring  Star “Centralized topology”  Mesh “They all connected together” n(n-1)/2
  3. 3. OSI MODEL Created by ISO Advantages: Divided the network into smaller and simpler components. Anything happening in in one layer doesn’t effect the other layers 7 layers: 1. Application layer 2. Presentation layer 3. Session layer 4. Transport layer 5. Network layer 6. Data link layer 7. Physical layer
  4. 4. APPLICATION LAYER “7” Is the interface between the actual application program. e.g.) File transfers, email …etc.
  5. 5. PRESENTATION LAYER “6” Responsible for format Data: Txt, video, audio …etc. Encrypt & decrypt the data. Compress & decompress the data.
  6. 6. SESSION LAYER Responsible for dialog control via 3 modes:  Simplex: Saying something and not getting a reply.  Half Duplex: two way communication but only send or receive at the same time. “e.g.) Walki Talkie”  Full Duplex: Send and receive at the same time “Like we talk in our life”
  7. 7. TRANSPORT LAYER “4” Take the data from the upper layers and reassemble & combine it in one data stream. 2 Protocols are integral to this layers: TCP & UDP. The Transport layer can either be connectionless or connection- oriented
  8. 8. CONNECTION ORIENTED COMMUNICATION “THREE WAY HANDSHAKE” I. The first segment is a request for synchronization called SYN. II. The next segment acknowledgement “SYN/ACK” III. The final segment is also acknowledgement to inform the receiver that the connection has been established. Characteristics: 1. A virtual circuit 2. It uses sequences 3. It uses flow control 4. It uses acknowledgement
  9. 9. DATA TRANSFER Flow Control 3 Types: Windowing, Buffering & congestion a voidance Windowing “Type of flow control”
  10. 10. ACKNOWLEDGEMENT If the receiver received all segment sent by the transmitting machine, it must send ACK to the sender to notify him that it has received all the segments and request the next segments, also once the sender send the segment it start a timer once it expire it start retransmitting the segments again.
  11. 11. NETWORK LAYER “3”  The Network layer, or layer 3, manages device addressing, tracks the location of devices on the network, and determines the best way to move data.  Responsible for routing.  Routing is finding a path on which data can pass from the source to destination.  Routers are Layer 3 devices  Data and route update packets are the two types of packets used at the Network layer:  Data packets These are used to transport user data through the internetwork. Protocols used to support data traffic are called routed protocols, and IP and IPv6 are key examples  Route update packets These packets are used to update neighboring routers about the networks connected to all routers within the internetwork. Protocols that send route update packets are called routing protocols; the most critical ones for CCNA
  12. 12. ROUTING TABLE EXPLANATION  NET -> Network addresses Protocol- specific network addresses.  INT -> Interface The exit interface a packet will take when destined for a specific network.  Metric The distance to the remote network. * Hops: are the number of router a packet passes through en route to a remote network A router in an internetwork. Each router LAN interface is a broadcast domain. Routers break up broadcast domains by default and provide WAN services.
  13. 13. THE DATA LINK LAYER “2”  Data Link layer will ensure that messages are delivered to the proper device on a LAN using hardware addresses and will translate messages from the Network layer into bits for the Physical layer to transmit.  As data is encoded with control information at each layer of the OSI model, the data is named with something called a Protocol Data Unit (PDU). At the Transport layer the PDU is called a Segment, Network layer is Packet, Data Link is Frame, and Physical layer is Bits.  Switches & bridges are layer 2 devices because it uses a specialized H/W called an ASIC “application-specific integrated circuit (ASIC)” * Latency is the time measured from when a frame enters a port to when it exits a port.
  14. 14. SWITCH EXPLANATION Sally will not hear Jon's frame because they are in different collision domains. Collision Domain: Each port on a bridge, a switch or a router is in a separate collision domain Broadcast Domain: All ports on a hub or a switch are by default in the same broadcast domain. All ports on a router are in the different broadcast
  15. 15. PHYSICAL LAYER “1”  Send bits & receive bits.  Hub is layer 1 device.
  16. 16. CSMA/CD When a collision occurs on an Ethernet LAN, the following happens: 1. A jam signal informs all devices that a collision occurred. 2. The collision invokes a random backoff algorithm. 3. Each device on the Ethernet segment stops transmitting for a short time until its backoff timer expires. 4. All hosts have equal priority to transmit after the timers have expired. * Backoff is the retransmission delay that’s enforced when a collision occurs, a host will resume transmission only after the forced time delay has
  17. 17. HALF DUPLEX & FULL DUPLEX
  18. 18. ETHERNET ADDRESSING OUIL Organizationally unique identifier by IEEE I/G: Individual/Group bit: • 0 -> MAC address can be located in the header • 1 -> broadcast/Multicast address in Ethernet. •G/L: Global/Local bit: • 0 -> Globally administration address, by IEEE. • 1 -> locally governed and administered address.
  19. 19. ETHERNET FRAME 1. Preamble An alternating 1,0 pattern provides a 5 MHz clock at the start of each packet 2. Start Frame Delimiter (SFD) is 10101011 3. Destination Address (DA) This transmits a 48-bit value using the least significant bit (LSB) fist. transmitting device. 5. Length or Type identify the Network layer protocol 6. Data This is a packet sent down to the Data Link layer from the Network layer. The size can vary from 46 to 1,500 bytes. 7. Frame Check Sequence (FCS) used to * When a receiving host receives the frame and runs the CRC, the answer should be the same. If not, the frame is discarded, assuming errors have occurred.
  20. 20. ETHERNET CABLING
  21. 21. CONTINUE ETHERNET CABLING
  22. 22. DATA ENCAPSULATION
  23. 23. PDU AND LAYER ADDRESSING
  24. 24. PORT NUMBERS AT THE TRANSPORT LAYER 0 ->1023 are reserved for well- known port numbers.
  25. 25. THREE-LAYER HIERARCHICAL MODEL
  26. 26. TRANSMISSION CONTROL PROTOCOL/INTERNET PROTOCOL (TCP/IP)  Created by DoD  TCP/IP is so popular because there were no set physical layer specifications, so it could run on any existing or future physical network
  27. 27. THE TCP/IP PROTOCOL SUITE
  28. 28. COMMON APPLICATION LAYER PROTOCOLS - PORTS AND TRANSPORT LAYER TECHNOLOGIES USED Protocol Port(s) TCP/UDP Description HTTP (Hypertext Transfer Protocol) 80 TCP  Used by Web servers to send web pages to clients’ Web browser (IE, Firefox, Opera) HTTPS (HTTP over SSL) 443 TCP  Provides a secure, encrypted connection  Padlock symbol is displayed in Web browser FTP (File Transfer Protocol) 20 & 21 TCP  Transfers files between servers & clients  20 – data  21 – control messages TFTP (Trivial File Transfer Protocol) 69 UDP  Transfers files between servers & clients  No login reqd SMTP (Simple Mail Transfer Protocol) 25 TCP  Used to send email messages between clients & servers and between servers POP3 (Post Office Protocol v 3) 110 TCP  Allows client software (Outlook Express, Pegasus) to retrieve email from mail server SNMP (Simple Network Management Protocol) 161 UDP  Allows network management applications to monitor devices remotely) Telnet 23 TCP  Allows user to log onto remote host (UNIX-based systems, routers, switches)and execute text-based commands NetBIOS 137, 138, 139 TCP  Used to route NetBIOS functionality over TCP/IP
  29. 29. COMMON APPLICATION LAYER PROTOCOLS - PORTS AND TRANSPORT LAYER TECHNOLOGIES USED Protocol Port(s) TCP/UDP Description NTP 123 UDP  Used to synchronize device on given network on the time DNS 53 UDP, TCP if size more than 512 bytes  Domain Name server DHCP 67 UDP  Assign IP addresses to hosts automatically/dynamically. IMAP 143, 993 with SSL TCP  Allows client software (Outlook Express, Pegasus) to retrieve email from mail server
  30. 30. DHCP PROCESS
  31. 31. TRANSPORT LAYER PROTOCOLS Transmission Control Protocol (TCP)
  32. 32. TRANSPORT LAYER PROTOCOLS User Datagram Protocol (UDP)
  33. 33. TCP vs UDP
  34. 34. THE INTERNET LAYER PROTOCOLS Internet Protocol (IP)
  35. 35. THE INTERNET LAYER PROTOCOLS Internet Control Message Protocol (ICMP): Buffer full/source quench If a router’s memory buffer for receiving incoming datagrams is full, it will use ICMP to send out this message alert until the congestion abates. Hops/time exceeded Each IP datagram is allotted a certain number of routers, called hops, to pass through. If it reaches its limit of hops before arriving at its destination, the last router to receive that datagram deletes it. Ping Packet Internet Groper (Ping) uses ICMP echo request and reply messages to check the physical and logical connectivity of machines on an internetwork.
  36. 36. ADDRESS RESOLUTION PROTOCOL (ARP)  Translate IP address to MAC address. * Reverse Address Resolution Protocol “RARP”: Translate MAC address to IP address.
  37. 37. REFERENCES * CCNA Routing and Switching Study Guide - Lammle, Todd * http://searchnetworking.techtarget.com * Interview questions: http://computernetworkingnotes.com/basic-networking-interview/questions-and- answers.html
  38. 38. THANK YOU 

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