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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
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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. |
- Changes in one
area do not affect other areas.
- Dividing the tasks
makes each element less complex.
- 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. |
- Upper layers convert
the message to data and send it to the Transport layer.
- The Transport layer
converts the data to segments and sends it down to the Network layer.
- The Network layer
converts the segments to packets and sends them to the Data Link layer.
- The Data Link layer
converts the packets to frames and sends them to the Physical layer.
- 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:
- Ethernet_II
- Ethernet_802.2
- Ethernet_802.3
- 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.
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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 eadulaney@anderson.edu.
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