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Step-By-Step Guide to the CCNA Exam, Part I
Need help studying for Cisco's CCNA exam? In this two-part series, our expert guides you through the CCNA exam objectives.

by Emmett Dulaney

9/18/2002 -- One of the most popular certification exams is the Cisco Certified Network Associate (CCNA) exam (#640-607), which leads to CCNA certification. This is a single-exam certification that also acts as a first step toward higher-level Cisco certifications such as the Cisco Certified Network Professional (CCNP). The exam is 75 minutes in length and now includes simulation-based questions. Between 45 to 55 questions are asked. The exam consists of eight major objective categories:

  • Bridging/Switching
  • OSI Reference Model & Layered Communications
  • Network Protocols
  • Routing
  • WAN Protocols
  • Network Management
  • LAN Design
  • Cisco Basics, IOS & Network Basics

PART II NOW LIVE
Editor's Note: Part II of this story is now live. To acces it, please click here.
In this article we will look at the first four objectives through a series of tables that list the sub-objectives for each and the information (or location to the information) you should know to prepare for this objective area. Next month, we will work through the remaining four objective categories. When we're done, you'll have a good general overview of all the material covered by the exam's objectives plus a solid collection of links for furthering your studies.

Objective #1: Bridging/Switching

Sub-Objective Information
Name and describe two switching methods. The two switching methods are store-and-forward and cut-through. With store-and-forward, the switch reads the entire frame (copying it into a buffer) and then does a CRC check before sending on (assuming no error).With cut-through, there is no error checking - thus decreasing latency. The forwarding is done after the header is read (and actually, only the destination MAC address of the header).
Distinguish between cut-through and store-and-forward LAN switching. This is a further itemization of the first objective. In cut-through switching, there is no CRC check done, and the packet is forwarded on based upon the address in the header. The whole packet does not even need to be received before being forwarded. With store-and-forward, the entire packet must be received and a CRC check done on it when it arrives. After the CRC check verifies the contents, then the packet is forwarded on toward its destination.
Describe the operation of the Spanning Tree Protocol and its benefits. The primary purpose of the Spanning Tree Protocol is to eliminate (as much as possible) loops. This is accomplished by blocking connections that can lead to loops. Cisco has published the PDF file, "Understanding Spanning-Tree Protocol" here.
Describe the benefits of virtual LANs. Virtual LANs allows managers to logically group networks that span topologies. This allows the manager/administrator to add, remove, and move devices as they need to and still maintain performance. Cisco's coverage of VLANs can be found in a PDF file here.


Objective #2: OSI Reference Model & Layered Communications

Sub-Objective Information
Describe data link and network addresses and identify key differences between them.

Data link addresses are physical addresses most often referred to as the MAC address (Media Access Control). MAC addresses are explored further in the next objective.

Network addresses exist at the Network layer and are logical (versus physical) addresses.

Define and describe the function of the MAC address.

MAC addresses are uniquely assigned to devices and there are no duplicates. They are hexadecimal addresses (12 digits) that are separated by dashes. The first six digits identify the manufacturer, and the last six identify the device.

The primary function of MAC addresses is to uniquely identify the network interface card (NIC) or other device. In TCP/IP, ARP (Address Resolution Protocol) is used to map the IP address (logical) to the MAC address (physical).

An example of a MAC address is: 00-03-47-3c-1c-25

List the key internetworking functions for the OSI Network layer. Rather than repeat what you already know if you've worked with networking for anytime at all, your time is best spent looking at what Cisco wants you to know for this objective at http://www.cisco.com/warp/public/535/2.html
Identify at least three reasons why the industry uses a layered model.
  1. Changes in one area do not affect other areas.
  2. Dividing the tasks makes each element less complex.
  3. Vendors can implement solutions at one or more layers without having to recreate the entire model.
Describe the two parts of network addressing; then identify the parts in specific protocol address examples.

The two parts of the network address are the network id and the host id. The division between the two, in TCP/IP, is obtained by comparing/contrasting the subnet mask against the IP address. You must know the three classes of host addresses (A, B, and C), and how to subnet, as detailed at: http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/ip.htm

Define and explain the five conversion steps of data encapsulation.
  1. Upper layers convert the message to data and send it to the Transport layer.
  2. The Transport layer converts the data to segments and sends it down to the Network layer.
  3. The Network layer converts the segments to packets and sends them to the Data Link layer.
  4. The Data Link layer converts the packets to frames and sends them to the Physical layer.
  5. The Physical layer converts the frames to 1's and 0's (electrical signals) and sends them across the network.

At each layer, header information is added. At the receiving end, the process is reversed, with headers being stripped off at each layer.

Describe connection-oriented network services and connectionless network service, and identify their key differences.

As the name implies, connection-oriented services must have a connection in order to communicate. A classic example of this is FTP, used to transfer files from one host to another. A connection must exist between the two hosts before communication can commence.

Connection-less protocols communicate without a dedicated connection existing. The classic example of this is e-mail -- when you send a message, it may reach the host it is intended for immediately or quite a while later. You send the e-mail without a dedicated connection.

In the world of TCP/IP, TCP is the Transport layer protocol that is used when a connection is required; while UDP is used in its place with a connection is not required. A primer from Cisco on understanding TCP/IP can be found here.

Identify the parts in specific protocol address examples.

This is basically commonsense and overlaps with earlier objectives. An IP address has two parts, and so on. You should review NetWare Protocols as posted here.

Describe the advantages of LAN segmentation.

LAN segmentation reduces the number of nodes per segment and makes administration easier, reduce bandwidth waste, and improve scalability.

Describe LAN segmentation using bridges.

The key issue is that the bridge relies upon the MAC address to determine whether the host to be reached is on this network segment or not. If the host is on this segment, then the data is left alone to travel throughout the network (and reach the host). If the host is not on this segment, then the data is sent across the bridge. Bridges can be used to connect two segments together, and no more than two.

An O.K. overview from Cisco can be found within this document.

Describe LAN segmentation using routers.

The router allows more than one segment to be communicated with. Instead of relying on MAC (layer 2) addresses, the router uses Network (layer 3) addresses. Click here for more information.

Describe LAN segmentation using switches.

Switches move the discussion into the VLAN realm and offer performance increases over other solutions due to physical definitions as opposed to logical, etc. The best overview for this topic can be found here.

Describe the benefits of network segmentation with bridges.

Click here.

Describe the benefits of network segmentation with routers

Click here.

Describe the benefits of network segmentation with switches

Click here.


Objective #3: Network Protocols

Sub-Objective Information
Describe the different classes of IP addresses (and subnetting)

There are five classes of IP addresses, distinguishable by the first digits (octet):

Class A - 0 to 126
Class B - 128 to 191
Class C - 192 to 223
Class D - 224 to 239
Class E - 240 to 255

Classes A, B, and C are used for assigning numbers to hosts, while Class D is generally used for Multicasting, and Class E is used for experimentation and broadcasting. The 127 octet range is reserved and cannot be used, as 127.0.0.1 is the loopback address for each host.

Using all of the numbers within the range, it is possible to have 16 million hosts on a Class A network, 65,000 on a Class B network, and 254 on a Class C network. Subnetting allows you to divide the network into a number of smaller networks, and reduces the number of hosts that can exist (overall and on each subnet).

The Cisco overview available here contains the necessary exam information on addresses and subnets.

Identify the functions of the TCP/IP network-layer protocol.

The Network layer is where IP addressing and routing take place. Not only does IP operate at this layer, but ICMP (Internet Control Message Protocol) does as well. Think: addressing, routing, and basic communication. Click here for more information.

Identify the functions performed by ICMP. ICMP first came about as a result of RFC 792 as an extension to IP. Most famous for the echo capabilities (ping), it supports packets that contain error, control, and information messages. Click here for more information.
Configure IP addresses.

IP addresses can be configured in one of two ways: manually or automatically. To configure addresses manually, you go to the host and enter an address that is unique within the scope of that host's communication range. This means that if the host is directly connected to the Internet, the address given to it must be unique within the entire Internet. On the other hand, if the host communicates only with a handful of other hosts, and reaches the Internet through a NAT (Network Address Translation) server, then the address need only be unique among the hosts it communicates directly with. Each operating system has a slightly different utility for entering the addressing information, but global among them all is the fact that you must not only enter the address for the host, but also related information. Related information includes the subnet mask, and can include such variables as the default gateway (router), DNS server, WINS server, etc.

To automatically configure hosts, you must set up a DHCP (Dynamic Host Configuration Protocol) server on your network and give it a pool (scope) of addresses that it can issue to hosts. The hosts contact the DHCP server and it leases them an address (and associated variables) from the pool for a set time period. If the information is no longer needed, it will be returned to the pool, but as long as it is needed, the host will continuously try to renew the lease from the server.

DHCP simplifies administration and management of IP addressing.

Verify IP addresses.

There are a number of tools that can be used to verify IP addresses. To see the values that have been assigned to a host, you can use the ipconfig utility with Windows NT and Windows 2000, or the winipcfg utility with Windows 9x. Similar functionality is present with the ifconfig utility in Unix and Linux.

You can test the address by pinging it from and seeing the response. Similarly, name resolution can be verified by pinging the host with the host name rather than the IP address.

The other primary utility you can use is trace (tracert/traceroute/etc. - dependent upon the operating system). This utility works like ping except not only does it show you that a response is received, but it will also show the hops taken to receive that response.

List the required IPX address and encapsulation type.

An IPX address, like an IP address, consists of two parts - network and host (node). 32 its of the address identify the network, while 48 bits identify the host for a total address of 80 bits.

IPX encapsulation occurs at the Data Link Layer and four types can be used over Ethernet:

  1. Ethernet_II
  2. Ethernet_802.2
  3. Ethernet_802.3
  4. Ethernet_SNAP (SubNetwork Access Protocol)

A description of the four types can be found here.

You can see the IPX address with the command:

Show IPX interface {interface}

Where {interface} is replaced by the name of the interface - such as "ethernet 0". Other commands that would be useful include:

Show ipx route

And

Show ipx traffic

For a list of IPX commands, click here.

Objective #4: Routing

Sub-Objective Information
Define flow control and describe the three basic methods used in networking. Flow control is used for data reliability -- to make sure the receiver gets the information sent by the sender in amounts that it can handle. This can be accomplished with buffering, sequencing and windowing, or acknowledgements of transmission. RFC 793 includes flow control as discusses sliding windows. The value of the sliding windows is that the size of the window is set by the receiver, thus allowing them to manage the flow of the information they can handle. Click here for more information.
Add the RIP routing protocol to your configuration.

To add RIP (Routing Information Protocol) to your configuration, the primary command is:

router rip

A list of all the commands employed can be found here.

Add the IGRP routing protocol to your configuration.

The primary way IGRP differs from RIP is in that each router with IGRP can have multiple default routes. To add IGRP (Interior Gateway Routing Protocol) to your configuration, the primary command is:

router igrp

Click here for more information.

Observations
A great deal has been made of the fact that this exam now includes simulation questions -- the change in number from 640-507 to 640-607 reflects that. While a new type of question was added, that was the only change: the content remains the same. This means that all the books on the market (and there are a proliferation of them) written to the 640-507 exam are still valid and can be used for exam study. Don't forget to check out the exam interface tutorial available here.

You'll also note from the links above that Cisco has posted most of the information that you need to know for the exam in a number of PDF files that are used for their own training and customer support. When studying for any exam, there is no better material you can find than that provided by the vendors themselves.

Lastly, the vast majority of information required for passing these objective categories should be known by anyone who has been a network administrator for any length of time at all. With a few exceptions, much of this same information has appeared on beginning networking exams (such as Microsoft's old Networking Essentials, and Novell's Networking Technologies) for years. Given that, this portion of the exam should not prove to be too much of a difficulty for most test-takers.

That's it until next month, when we'll cover the rest of this exam's objectives.

Questions or comments on this article? Post your thoughts below! Want to be notified as soon as Part 2 is published? Sign up for CertCities.com's e-mail newsletter.


Emmett Dulaney is the author of several books on Linux, Unix and certification. He can be reached at .

 

 

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