INTRODUCTION TO CISCO NETWORKING TECHNOLOGIES (641-821)

1. The primary advantage of bridging is increased bandwidth available on a segment because of the decreased number of devices in the collision domain.

2. Switches have the same basic functionality as bridges but they usually have more ports. Each switch port is a separate collision domain, and each port provides dedicated bandwidth.

3. Virtual local area networks (VLANs) can be used to make a group of switch ports into a separate, isolated LAN. Routing is required for communication between VLANs.

4. VLANs can function across multiple switches when they are connected by a trunk connection. Inter-switch linking (ISL) is used to create a trunk connection between Fast Ethernet ports on Cisco switches.

5. Switches make it possible to run Ethernet devices in full-duplex mode. In full-duplex mode, two devices share the Ethernet wire simultaneously and exclusively, enabling faster throughput because very few collisions are possible.

6. Store-and-forward switching reads the entire frame before making a forwarding decision; cut-through switching reads only the first six bytes ”the destination media access control (MAC) address ”to make a forwarding decision. Store-and-forward switching performs error checking; cut-through switching does not.

7. The primary advantages of routers are

   • They allow you to connect dissimilar LANs

   • They provide multiple paths to a destination network

   • They allow the interconnection of large and complex networks

8. Connection-oriented communication uses a nonpermanent path for data transfer. It involves three steps: establish the connection, transfer the data, and terminate the connection. A practical example of a connection-oriented communication would be a walkie-talkie conversation where the connection has to be established each time to the receiver by pressing a button, and once you are finished talking you release the button until you want to talk again. Connectionless communication uses a permanently established link. An example of a connection-oriented protocol is TCP and an example of connectionless communication protocol is UDP. Again, a practical example would be that of a telephone conversation where a connection is made and maintained throughout the duration of the call.

9. The layers of the OSI model are Application layer, Presentation layer, Session layer, Transport layer, Network layer, Data Link layer, and Physical layer.

   7. Application

   6. Presentation

   5. Session

   4. Transport

   3. Network

   2. Data Link

   1. Physical

10. Encapsulation, or tunneling, takes frames from one network system and places them inside frames from another network system.

11. The Presentation layer concerns itself with data representation, data encryption, and data compression. It supports different protocols for text, data, sound, video, graphics, and images, such as ASCII, MIDI, MPEG, GIF, and JPEG.

12. The Session layer establishes, manages , and terminates sessions between applications. Network file system (NFS), structured query language (SQL), and remote procedure calls (RPCs) are examples of Session layer protocols.

13. The Transport layer sits between the upper and lower layers of the OSI model. It performs flow control by buffering, multiplexing, and parallelization . It provides end-to-end data transport services by segmenting upper-layer applications, establishing an end-to-end connection, sending segments from one end host to another, and ensuring reliable data transport.

14. The primary functions of the Network layer of the OSI model are path determination and packet switching. In addition, remember that the Network layer is the domain of routing.

15. The primary functions of the Data Link layer of the OSI model are:

    • Allows the upper layers of the OSI model to work independently of the physical media

    • Performs physical hardware addressing

    • Provides optional flow control

    • Generates error notification

16. Convergence occurs when all routers in an internetwork agree on optimal routes. A routing loop occurs when a packet bounces back and forth between two or more routers.

17. Distance vector routing protocols send their entire routing tables to their neighbors. Link state protocols send the state of their own interfaces to every router in the internetwork.

18. Counting to infinity is a problem for distance vector routing protocols. It can be eliminated or mitigated by using the following techniques: maximum hop count, split horizon, route poisoning , and hold-down timers.

19. TCP provides a connection-oriented and reliable service to the applications that use its services with the use of acknowledgments, sequence number checking, error and duplication checking, and the TCP three-way handshake. User Datagram Protocol (UDP) provides a connectionless and best-effort service to the applications that use its services.

20. Well-known port numbers include:

    • File Transfer Protocol (FTP) 21

    • Telnet 23

    • Simple Mail Transfer Protocol (SMTP) 25

    • Domain Name System (DNS) 53

    • TFTP 69

    • Simple Network Management Protocol (SNMP) 161, 162

    • HTTP 80

21. Address Resolution Protocol (ARP) maps a known IP address to a physical address. Reverse Address Resolution Protocol (RARP) maps a known physical address to a logical address.

22. Understand the basic concepts of IP addressing. Dotted-decimal notation is the decimal representation of a 32-bit IP address. The dotted -decimal notation represents the four octets of bits by performing binary-to-decimal conversion for each octet and providing a decimal value for each octet.

23. You should know the decimal representation of classes A, B, and C addresses as well as the number of networks and nodes each supports as shown below:

    • Class A : 1 through 126

    • Class B : 128 through 191

    • Class C : 192 through 223

24. You should be able to recognize the default mask for each class of IP address as shown below:

    • Class A : 255.0.0.0

    • Class B : 255.255.0.0

    • Class C : 255.255.255.0

25. The network number and broadcast address for a given subnet are the first and last IP addresses, respectively. The range of usable IP addresses is all addresses between the network number and broadcast address. In binary format, the network number has all of the host bits of the address set to 0. The broadcast address has all of the host bits set to 1.

26. You should know how to do subnetting tasks very quickly. It will save you valuable time in the end.

27. The interface between the customer network and the WAN provider network occurs between the data terminal equipment (DTE) and the data communication equipment (DCE). DTE devices are usually routers. DCE devices are usually modems, channel service units/data service units (CSUs/DSUs), and terminal adapter/network terminations 1 (TA/NT1s).

28. Frame relay is a high-speed, packet-switching WAN protocol that operates at the Data Link layer. It runs on nearly any type of serial interface, uses frame check sequence (FCS) as its error-checking mechanism, and relies on a discard eligibility bit for congestion management. A virtual circuit must connect two DTE devices within a frame relay network. Permanent virtual circuits (PVCs) are more widely used than switched virtual circuits (SVCs) in frame relay networks.

29. Data link connection identifier (DLCI) serves as the addressing scheme within a frame relay network. Local Management Information (LMI) is a set of enhancements to frame relay that was developed by Cisco, StrataCom, Northern Telecom, and DEC. Cisco routers support LMI variations for American National Standards Institute (ANSI), Q933a, and Cisco.

30. DLCIs are mapped to network layer addresses through inverse ARP or by using the frame-relay map command.

31. Committed Information Rate (CIR) is the rate, in bits per second, at which data is transferred across the frame relay network.

32. Password Authentication Protocol (PAP) uses a two-way handshake to authenticate Point-to-Point Protocol (PPP) connections and transmits username/password information in clear text. Challenge Handshake Authentication Protocol (CHAP) uses a three-way handshake and relies on secret, encrypted passwords and unique IDs to authenticate PPP.

33. Integrated services digital network (ISDN) can be ordered as either basic rate interface (BRI) or primary rate interface (PRI). ISDN functions represent devices or hardware functions within ISDN. Reference points describe the logical interfaces between functions.

34. ISDN can be used to add bandwidth for telecommuting , improve Internet response time, carry multiple network layer protocols, and encapsulate other WAN services.

35. Dial-on-demand routing (DDR) works with ISDN to establish and terminate connections. It uses access lists to look for interesting traffic.