Table Of ContentCCNA Study Guide v2.44 – Aaron Balchunas 1
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Cisco CCNA Study Guide
v2.44 © 2011
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Aaron Balchunas
CCNA Study Guide v2.44 – Aaron Balchunas 2
Table of Contents
Part I – General Networking Concepts
Section 1 Introduction to Networking
Section 2 OSI Reference Model
Section 3 Ethernet Standards
Section 4 Hubs vs. Switches vs. Routers
Section 5 STP
Section 6 IPv4 Addressing and Subnetting
Section 7 TCP and UDP
Section 8 IPv6 Addressing
Section 9 Introduction to 802.11 Wireless
Part II – The Cisco IOS
Section 10 Router Components
Section 11 Introduction to the Cisco IOS
Section 12 Advanced IOS Functions
Part III - Routing
Section 13 The Routing Table
Section 14 Static vs. Dynamic Routing
Section 15 Classful vs. Classless Routing
Section 16 Configuring Static Routes
Section 17 RIPv1 & RIPv2
Section 18 IGRP
Section 19 EIGRP
Section 20 OSPF
Part IV – VLANs, Access-Lists, and Services
Section 21 VLANs and VTP
Section 22 Access-Lists
Section 23 DNS and DHCP
Part V - WANs
Section 24 Basic WAN Concepts
Section 25 PPP
Section 26 Frame-Relay
Section 27 NAT
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Part I
General Networking Concepts
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Section 1
- Introduction to Networking -
What is a Network?
Α network is defined as devices connected together to share information
and services. The types of data/services that can be shared on a network is
endless - documents, music, email, websites, databases, printers, faxes,
telephony, videoconferencing, etc.
Protocols are “rules” that govern the method by which devices share data
and services. Protocols are covered in great detail in subsequent sections.
Basic Network Types
Networks are generally broken down into two types:
LANs (Local Area Networks) - a high-speed network that covers a
relatively small geographic area, usually contained within a single building
or campus. A LAN is usually under the administrative control of a single
entity/organization.
WANs (Wide Area Networks) – The book definition of a WAN is a
network that spans large geographical locations, usually to interconnect
multiple LANs.
A more practical definition describes a WAN as a network that traverses a
public network or commercial carrier, using one of several WAN
technologies. Thus, a WAN can be under the administrative control of
several entities or organizations, and does not need to “span large
geographical distances.”
Note: Occasionally, books will define a third type of network known as a
MAN (Metropolitan Area Network). A MAN is defined as a network that
spans several LAN’s across a city-wide geographic area. The term “MAN”
is less prevalent than either LAN or WAN.
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Network “Architectures”
A host refers to any device that is connected to your network. Some define a
host as any device that has been assigned a network address.
A host can serve one or more functions:
• A host can request data (often referred to as a client)
• A host can provide data (often referred to as a server)
• A host can both request and provide data (often referred to as a peer)
Because of these varying functions, multiple network “architectures” have
been developed, including:
• Peer-to-Peer networks
• Client/Server networks
• Mainframe/Terminal networks
When using a peer-to-peer architecture, all hosts on the network can both
request and provide data and services. For example, configuring two
Windows XP workstations to share files would be considered a peer-to-peer
network.
Though peer-to-peer networks are simple to configure, there are several key
disadvantages to this type of architecture. First, data is spread across
multiple devices, making it difficult to manage and back-up that data.
Second, security becomes problematic, as you must configure individual
permissions and user accounts on each host.
When using a client/server architecture, hosts are assigned specific roles.
Clients request data and services stored on Servers. Connecting Windows
XP workstations to a Windows 2003 domain controller would be considered
a client/server network.
While client/server environments tend to be more complex than peer-to-peer
networks, there are several advantages. With data now centrally located on
a server or servers, there is only one place to manage, back-up, and secure
that data. This simplified management allows client/server networks to scale
much larger than peer-to-peer. The key disadvantage of client/server
architecture is that it introduces a single point of failure.
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Network “Architectures” (continued)
When using a mainframe/terminal architecture, often referred to as a thin-
client environment, a single device (the mainframe) stores all data and
services for the network. This provides the same advantage as a client/server
environment – centralized management and security of data.
Additionally, the mainframe performs all processing functions for the dumb
terminals (or thin-clients) that connect to the mainframe. The thin clients
perform no processing whatsoever, but serve only as input and output
devices into the mainframe. Put more simply, the mainframe handles all the
“thinking” for the thin-clients.
A typical hardware thin-client consists of a keyboard/mouse, a display, and
an interface card into the network. Software thin-clients are also prevalent,
and run on top of a client operating system (such as Windows XP or Linux).
Windows XP’s remote desktop is an example of a thin-client application.
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Section 2
- OSI Reference Model -
Network Reference Models
As computer network communication grew more prevalent, the need for a
consistent standard for vendor hardware and software became apparent.
Thus, the first development of a network reference model began in the
1970’s, spearheaded by an international standards organization.
A network reference model serves as a blueprint, dictating how network
communication should occur. Programmers and engineers design products
that adhere to these models, allowing products from multiple manufacturers
to interoperate.
Network models are organized into several layers, with each layer assigned
a specific networking function. These functions are controlled by protocols,
which govern end-to-end communication between devices.
Without the framework that network models provide, all network hardware
and software would have been proprietary. Organizations would have been
locked into a single vendor’s equipment, and global networks like the
Internet would have been impractical or even impossible.
The two most widely recognized network reference models are:
• The Open Systems Interconnection (OSI) model
• The Department of Defense (DoD) model
The OSI model was the first true network model, and consisted of seven
layers. However, the OSI model has become deprecated over time, replaced
with more practical models like the TCP/IP (or DoD) reference model.
Network models are not physical entities. For example, there is no OSI
device. Devices and protocols operate at a specific layer of a model,
depending on the function. Not every protocol fits perfectly within a specific
layer, and some protocols spread across several layers.
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OSI Reference Model
The Open Systems Interconnection (OSI) model was developed in the
1970’s and formalized in 1983 by the International Organization for
Standardization (ISO). It was the first networking model, and provided the
framework governing how information is sent across a network.
The OSI Model (ISO standard 7498) consists of seven layers, each
corresponding to a particular network function:
7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data-link
1 Physical
Various mnemonics have been devised to help people remember the order of
the OSI model’s layers:
7 Application All Away
6 Presentation People Pizza
5 Session Seem Sausage
4 Transport To Throw
3 Network Need Not
2 Data-link Data Do
1 Physical Processing Please
The ISO further developed an entire protocol suite based on the OSI model;
however, this OSI protocol suite was never widely implemented. More
common protocol suites can be difficult to fit within the OSI model’s layers,
and thus the model has been mostly deprecated.
A more practical model was developed by the Department of Defense
(DoD), and became the basis for the TCP/IP protocol suite (and
subsequently, the Internet). The DoD model is explained in detail later in
this guide.
The OSI model is still used predominantly for educational purposes, as
many protocols and devices are described by what layer they operate at.
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The Upper Layers
The top three layers of the OSI model are often referred to as the upper
layers. Thus, protocols that operate at these layers are usually called upper-
layer protocols, and are generally implemented in software.
The function of the upper layers of the OSI model can be difficult to
visualize. The upper layer protocols do not fit perfectly within each layer;
and several protocols function at multiple layers.
The Application layer (Layer 7) provides the actual interface between the
user application and the network. The user directly interacts with this layer.
Examples of application layer protocols include:
• FTP (via an FTP client)
• HTTP (via a web-browser)
• SMTP (via an email client)
• Telnet
The Presentation layer (Layer 6) controls the formatting of user data,
whether it is text, video, sound, or an image. The presentation layer ensures
that data from the sending device can be understood by the receiving device.
Additionally, the presentation layer is concerned with the encryption and
compression of data.
Examples of presentation layer formats include:
• Text (RTF, ASCII, EBCDIC)
• Music (MIDI, MP3, WAV)
• Images (GIF, JPG, TIF, PICT)
• Movies (MPEG, AVI, MOV)
The Session layer (Layer 5) establishes, maintains, and ultimately
terminates connections between devices. Sessions can be full-duplex (send
and receive simultaneously), or half-duplex (send or receive, but not
simultaneously).
The four layers below the upper layers are often referred to as the lower
layers, and demonstrate the true benefit of learning the OSI model.
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The Transport Layer
The Transport layer (Layer 4) is concerned with the reliable transfer of
data, end-to-end. This layer ensures (or in some cases, does not ensure) that
data arrives at its destination without corruption or data loss.
There are two types of transport layer communication:
• Connection-oriented - parameters must be agreed upon by both
parties before a connection is established.
• Connectionless – no parameters are established before data is sent.
Parameters that are negotiated by connection-oriented protocols include:
• Flow Control (Windowing) – dictating how much data can be sent
between acknowledgements
• Congestion Control
• Error-Checking
The transport layer does not actually send data. Instead, it segments data
into smaller pieces for transport. Each segment is assigned a sequence
number, so that the receiving device can reassemble the data on arrival.
Examples of transport layer protocols include Transmission Control
Protocol (TCP) and User Datagram Protocol (UDP). Both protocols are
covered extensively in another guide.
Sequenced Packet Exchange (SPX) is the transport layer protocol in the
IPX protocol suite.
The Network Layer
The Network layer (Layer 3) has two key responsibilities. First, this layer
controls the logical addressing of devices. Logical addresses are organized
as a hierarchy, and are not hard-coded on devices. Second, the network layer
determines the best path to a particular destination network, and routes the
data appropriately.
Examples of network layer protocols include Internet Protocol (IP) and
Internetwork Packet Exchange (IPX). IP version 4 (IPv4) and IP version 6
(IPv6) are covered in nauseating detail in separate guides.
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