Chapter 1. Practical Lab Methodology and Equipment

CCNA Practical Studies is a book dealing with the application of knowledge, not just the accumulation of knowledge. Our intention and hope is that, by the end of the book, your confidence and skill level in configuring and troubleshooting Cisco devices will have greatly increased. We ourselves came through the ranks of CCNA, CCNP, and CCIE, and through those experiences we learned that knowing networking theory is much different than configuring a networking device to operate according to that theory. During the certification process, we often experienced the frustration of understanding networking concepts but lacked the knowledge of how to configure networking devices according to those concepts in a real-world environment. These experiences made us feel that more hands-on experience was needed to help grasp the configuration tasks necessary to configure Cisco devices from start to finish. For this purpose, we have developed this book. Our approach to this book is simple:

  • To give you an opportunity to configure, step by step, a completely functional network with multiple routing protocols and ISDN dial backup

By doing so, you will be able to see and understand the impact that each command has and understand the method of configuring a network from scratch.

OSI Reference Model

Our method to configuring this network will follow the OSI reference model. The OSI model was developed to help break internetworking concepts into areas that can be identified and separated from other concepts. This helps you to understand the different tasks that must be completed to obtain internetwork connectivity. The advantages of having a layered approach are listed here:

  • Enables specialization in each of the layers
  • Reduces the complexity of the entire process by breaking up complex operations into simple elements
  • Provides an opportunity to define standards at each layer that are independent of the other layers
  • Provides a method to troubleshooting internetworking issues

Table 1-1 illustrates the OSI reference model.

Table 1-1. OSI Reference Model

Layer 7 Application
Layer 6 Presentation
Layer 5 Session
Layer 4 Transport
Layer 3 Network
Layer 2 Data link
Layer 1 Physical

Before getting into the methodology behind the OSI model and this book, review Table 1-2, which delves into the seven layers of the OSI model individually.

Table 1-2. OSI Reference Model Layers

Layer Name Functional Description Examples
Application (Layer 7) An application that communicates with other computers is implementing OSI application layer concepts. The application layer refers to communications services to applications. For example, a word processor that lacks communications capabilities would not implement code for communications, and word processor programmers would not be concerned about OSI Layer 7. However, if an option for transferring a file were added, the word processor would need to implement OSI Layer 7 (or the equivalent layer in another protocol specification). Telnet, HTTP, FTP, WWW browsers, NFS, SMTP gateways (Eudora, CC:mail), SNMP, X.400 mail, FTAM
Presentation (Layer 6) This layer's main purpose is defining data formats, such as ASCII text, EBCDIC text, binary, BCD, and JPEG. Encryption also is defined by OSI as a presentation layer service. For example, FTP enables you to choose binary or ASCII transfer. If binary is selected, the sender and receiver do not modify the contents of the file. If ASCII is chosen, the sender translates the text from the sender's character set to a standard ASCII and sends the data. The receiver translates back from the standard ASCII to the character set used on the receiving computer. JPEG, ASCII, EBCDIC, TIFF, GIF, PICT, encryption, MPEG, MIDI
Session (Layer 5) The session layer defines how to start, control, and end conversations (called sessions). This includes the control and management of multiple bidirectional messages so that the application can be notified if only some of a series of messages are completed. This allows the presentation layer to have a seamless view of an incoming stream of data. The presentation layer can be presented with data if all flows occur, in some cases. For example, an automated teller machine transaction in which you withdraw cash from your checking account should not debit your account and then fail before handing you the cash, recording the transaction even though you did not receive money. The session layer creates ways to imply which flows are part of the same session and which flows must complete before any are considered complete. RPC, SQL, NFS, NetBIOS names, AppleTalk ASP, DECnet SCP
Transport (Layer 4) Layer 4 includes the choice of protocols that either do or do not provide error recovery. Multiplexing of incoming data for different flows to applications on the same host (for example, TCP sockets) also is performed. Reordering of the incoming data stream when packets arrive out of order is included. TCP, UDP, SPX
Network (Layer 3) This layer defines end-to-end delivery of packets. To accomplish this, the network layer defines logical addressing so that any endpoint can be identified. It also defines how routing works and how routes are learned so that the packets can be delivered. The network layer also defines how to fragment a packet into smaller packets to accommodate media with smaller maximum transmission unit sizes. (Note: Not all Layer 3 protocols use fragmentation.) The network layer of OSI defines most of the details that a Cisco router considers when routing. For example, IP running in a Cisco router is responsible for examining the destination IP address of a packet, comparing that address to the IP routing table, fragmenting the packet if the outgoing interface requires smaller packets, and queuing the packet to be sent out to the interface. IP, IPX, AppleTalk DDP, ICMP
Data link (Layer 2) The data link (Layer 2) specifications are concerned with getting data across one particular link or medium. The data link protocols define delivery across an individual link. These protocols are necessarily concerned with the type of media in question; for example, 802.3 and 802.2 are specifications from the IEEE, which are referenced by OSI as valid data link (Layer 2) protocols. These specifications define how Ethernet works. Other protocols, such as High-Level Data Link Control (HDLC) for a point-to-point WAN link, deal with the different details of a WAN link. As with other protocol specifications, OSI often does not create any original specification for the data link layer but instead relies on other standards bodies such as IEEE to create new standards for the data link layer and the physical layer. IEEE 802.3/802.2, HDLC, Frame Relay, PPP, FDDI, ATM, IEEE 802.5/802.2
Physical (Layer 1) These physical layer (Layer 1) specifications, which are also typically standards from other organizations that are referred to by OSI, deal with the physical characteristics of the transmission medium. Connectors, pins, use of pins, electrical currents, encoding, and light modulation are all part of different physical layer specifications. Multiple specifications are sometimes used to complete all details of the physical layer. For example, RJ-45 defines the shape of the connector and the number of wires or pins in the cable. Ethernet and 802.3 define the use of wires or pins 1, 2, 3, and 6. So, to use a Category 5 cable with an RJ-45 connector for an Ethernet connection, Ethernet and RJ-45 physical layer specifications are used. EIA/TIA-232, V.35, EIA/TIA- 449, V.24, RJ45, Ethernet, 802.3, 802.5, FDDI, NRZI, NRZ, B8ZS

As you configure the network, you will deal mostly in Layers 1 through 4. Our approach to the network configuration task is to start at the physical layer, complete the configuration task for the physical layer, move on to the data link layer configuration task, and so on until you have completed all the configuration tasks and the network is up and operational. Later chapters in the book get into more detail in terms of configuration tasks. This method enables you to identify all needed configuration tasks for each layer, remembering that if the physical layer configuration tasks are not completed, the data link configuration task will not produce the desired result because they are dependant on the physical layer. This is true with the network layer as well—if the data link configuration tasks are not completed or are completed incorrectly, the network layer (primarily routing) will not function correctly.

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