The Comptia Network

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The Comptia Network+ examination is not an unbeatable monster. In fact, compared to many common

certification examinations, the Network+ exam is rather formulaic and easy to master with the righttraining. In this study guide, you will receive just that right training; in fact, you can master the facts you

need to know for the exam in 20 easy lessons. Each lesson is timed to take approximately one hour to

complete (which is a very generous estimate indeed); many people will be able to read the covered

material in less than half of that time.

Most of the lessons will follow a similar format content will be covered, with key points in bold, in a

small reading section, followed by a few questions for review. It is recommended that you read the section

multiple times to fully comprehend the material, as many of the key points covered come straight out of

exam pattern or theComptia Network+ examsyllabus. The review questions will almost always cover

concepts directly addressed in the reading sections and will also reflect typical exam questions.

Periodically, you will encounter some reading sections in which exam material is not directly

addressed, such as in the troubleshooting or review reading sections. Dont be fooled these areperhaps the most critical passages in helping you succeed on the exam because they cover the concepts

and methods necessary to be successful in answering exam questions, especially those requiring some

analysis.

After you have completed all 20 days of the Network+ study guide, you will probably be ready for the exam

(of course, you may want to check out ourSneak Peek Review.) So, it would be in your interest to

register for the exam ahead of schedule, but do know that you dont have to pay full price for the exam

many online companies offer reduced-price exams and a quick search on our forum will yield some of

these providers (also go through the article section formore details on vouchers).

The most important thing to remember while studying for this exam is that it tests primarily for your ability to

apply the relatively small amount of information covered by the exam to solve basic network issues. So,

when studying, dont simply memorize names and functions; instead, memorize the applications, pros, andpitfalls of all the networking components. Do this and you will succeed in your endeavor to earn the

Network+ certification!

Day 1:Network Topologies & Types Of Networks

Day 2:The OSI Model

Day 3:Networking Equipment - I

Day 4:Networking Equipment - II

Day 5:Understanding Frame Types, Especially Ethernet
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Day 6:Understanding Wireless

Day 7:TCP/IP Addressing and IPv6

Day 8:Protocols of the TCP/IP Protocol Suite

Day 9:NAT and ICS

Day 10:DHCP, Port Forwarding, and DMZ Hosts

Day 11:TCP/IP Troubleshooting Tools

Day 12:NetBIOS

Day 13:Network Troubleshooting - A Case Study

Day 14:Common Protocol Suites

Day 15:DNS

Day 16:WAN Technologies

Day 17:Network Management

Day 18:Remote Access

Day 19:Repair Tools

Day 20:Final Review Questions

Network Topologies & Types Of Networks

Topologies

Networking topologies are organized by the way in which information "flows" across a network. Below are

the basic topologies:

At the core of the Network+ exam and networking concepts in general is the idea of topology, or more

specifically, the manner in which data is exchanged over the network. Network topology is a mainly

conceptual topic - when we speak of "star" networks or "ring" networks, we are really speaking in terms of

the manner in which information is exchanged and not their physical setup. Remember that each

topology/network type has its unique advantages and disadvantages that will be tested on the

Network+ exam in the form of asking you "which is the most appropriate." Don't try to memorize the perks ofeach - rather, try to understand the manner in which each allows the exchange of information; then, the

advantages and disadvantages will seem only logical to you.

Bus - This is the most simplistic topology in which the nodes of the network are individually linked to up to

two successive othe nodes or another node and a terminating node or terminator. This is considered now an

archaic topology, because of the difficulty of troubleshooting network issues (how do you know which

node is causing the connection issue?), redundancy issues (if one node fails, the network as a whole

can fail), the need for terminators, and the amount of traffic created (every node between A and B must

receive the packet that A sends). The nodes linked in this topology are often referred to as "daisy-

chained."

Ring - Similar to a bus network in that nodes are linked to each other, but dissimilar in that the ends of a ring

network are not terminated because, well, there are no ends! A ring network is something like a "circular"

network in which each and every node is linked to two other nodes. This shares many of the same

weaknesses as the bus topology, including troubleshooting difficulty, redundancy issues, and traffic created,

and also adds an additional difficulty - the difficulty of adding a node to a token ring network.
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Star - This is the most typical and practical network setup. In a star network, each node maintains an

individual connection to a switch, where all other nodes are connected. Traffic between two known nodes,

therefore, only goes through the switch and not through other nodes. This increases the redundancy of the

network (one computer faltering will not cause the network to fail), increases data privacy (unicast traffic

does not travel through all nodes), and is a relatively easy-to-use setup. Disadvantages include reliance onthe switch (a fail-point) and the amount of wiring necessary.

Mesh/"Ad Hoc" - This is a rarely occurring configuration in which every node is connected to every other

node; it usually occurs only in wireless networks in "ad hoc" mode, which will be discussed later; in this

mode, each wireless card maintains a connection to each other wireless node it wishes to connect with,

forming a "mesh" of a network. This is a relatively easy to understand option but is inefficient, requires a

large amount of overhead, and is difficult to manage.

Combined or Hybrid - This is simply a topology referring to the case where more than one topology isutilized. For example, you may have three token ring networks connected to a central hub, forming a star of

token rings. This is one of many possibilities of a hybrid network.

Types of Networks (Access Models)

The Network+ examination is interested in your ability to identify network access models, generally referred

to as types of networks. This does not suggest the way in which network nodes are connected or the way

that information flows (as do topologies), but rather, the manner and mode in which nodes communicate

with each other and share information. There are three basic types:

Decentralized - Often referred to as "peer to peer" network, a decentralized network does not contain any

distinctions between client and server. In a decentralized network, every node acts as a client and/or a

server depending on the task at hand. For example, many file sharing networks are considered

"decentralized" because nodes both download and upload (serve) files. The ease of adding nodes and the

ease of setup is a drawing point of decentralized networks, but the pivotal downfall of these networks is their

difficulty of maintenance (a setting must be changed on each node to reflect a setting change on the whole

network).

Client-Server Access - In this type, nodes can either act as "clients" or "servers," requesting or handing out

information. Do not confuse the model with the star topology; though the star topology often utilizes the

client-server access model, this does not infer that every client-server network utilizes the star topology. In aclient-server network, management is easy and the network can offer services that decentralized

networks cannot, but this comes at the expense of difficulty in setup, setup cost, and server reliance.

Centralized - A centralized network is a modified client-server network in which the clients have no

individual control; that is, all maintenance and setup occurs at the server level. The extreme ease of


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management and ability to micromanage is a drawing point of this access method, but the prohibitive

cost and inflexibility of the method deter many from employing it.

The OSI Model

Contents

1 The Open Systems Interconnection (OSI) Model

2 Physical (Layer 1)

3 Data Link (Layer 2)

o 3.1 Sublayerso 3.2 Protocols

4 Network (Layer 3)

5 Transport (Layer 4)

6 Session (Layer 5)

7 Presentation (Layer 6)

8 Application (Layer 7)

9 Conclusion

The Open Systems Interconnection (OSI) Model

At the core of the Network+ exam is the OSI "Seven" Model. The model describes the ways and meansthat networks use to operate and for communication . Though you will seldom (if ever) encounter or use

it in practice, and although you will find it to be a mundane, ambiguous, or even arbitrary model, it is heavily

tested on the Network+ exam and therefore for our purposes, it is immediately relevant.

The OSI Model is like a seven-layered cake. Just like the cake the OSI Model is a LIE and will never help

you in life. But I digress, as the cake starts from the bottom and becomes more ornate as it reaches the top,

the OSI Model begins with the most basic layer, the Physical layer, and ends at the layer that we as users

encounter, the Application layer. Like a cake, each of the layers depends on the layers below it to

operate - for example, Outlook Express cannot receive email when the network cable is disconnected -

without the cable, the "cake" crumbles. (OK, this analogy is a bit of a stretch, but just go with it!) The order of

the layers, therefore, is quite important and you should have it intimately memorized.

Here are the layers, from bottom to top:

Name MnemonicLayer

Number

Application All 7

Presentation People 6

Session Seem 5
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Transport To 4

Network Need 3

Data Link Data 2

Physical Processing 1

Of course, you are free to come up with your own mnemonic device, but we do recommend you find some

way of remembering the layers because it will be a subject of the test. Which is not a lie, unfortunately.

More important than the order of the layers, however, is the function of the layers. Most exam questions on

the OSI model ask you, "Which layer does so-and-so operate in?" or something to that nature. Another

type of question that occurs frequently is, "A problem has occurred (Problem description). Which layer

is to blame ?" These questions can feel ambiguous or difficult, but most of the time, there is a single, clear

answer that makes itself known provided that you are aware of the model and the place each layer takes in

the model. We will now cover each layer in detail.

Physical (Layer 1)

At the base of the OSI model is the physical layer. This one is the easiest to understand - it encompasses

most of the physical aspects of the network; for example, a repeater (a piece of equipment that amplifies

signals) operates at the physical level because it is only concerned with transmitting the electric signal on

the wire - it does not try to interfere with, encode/decode, or otherwise logically manipulate the signal. Think

of the physical layer as the "electrical" layer of the model - the physical layer is the layer of low-level

networking equipment, such as some hubs, cabling, and repeaters . The physical layer is never

concerned with protocols or other such higher-layer items.

Examples of hardware in this layer:

Network adapter

Repeater

Network hub

Modem

Fiber Media Converter

Data Link (Layer 2)

The Data Link Layer transfers data between adjacent nodes in a Wide Area Network, or between nodes on

any given Local Area Network. This layer also provides the procedural means to transfer data betweennetwork entities and sometimes to detect and correct errors that have occurred within the Physical Layer.

Since the Data Link layer is concerned primarily with local delivery within a LAN, data link frames do not

cross the boundaries of a local network segment and instead focus on local delivery, addressing, and media

arbitration.

Switches operate in the Data Link layer.


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Sub layers

The Data Link Layer is often subdivided into two sublayers, the LLC Sublayer and the MAC Sublayer:

The LLC (or Logical Link Control) Sublayer multiplexes protocols running atop the Data Link

Layer, and provides flow control, acknowledgement, and error control. It also specifies the

mechanisms to be used for addressing stations and for controlling the data exchanged between

machines.

The MAC (or Media Access Control) Sublayer determines who is allowed to access the media at

any one time (as in CSMA/CD) and provides frame synchronization, which determines where one

frame ends and the next begins.

Protocols

Protocols in the Data Link Layer include:

Ethernet for LANs

PPP

HDLC

ADCCP for point-to-point connections

PTPPD Point-to-Point Portal Device

Network (Layer 3)

The Network layer is where the frames of the Data Link layer become packets. It can be described as the

puberty of the OSI model. It is where the boys of the Data Link layer become men. The best way to think of

the Network layer is as the mailroom clerk of the OSI model. The clerk receives mail and directs it to the

appropriate couriers. In similar fashion, the Network layer translates the frames it receives from the Data

Link layer into more logical packets which can be routed to other networks (like sending it to a courier). At

the Network layer, you can begin to actually communicate across a Network, but the service is called

"unreliable" because no connection can be established. Communication over the Network layer is something

like throwing a message in a bottle into the sea or hollowing out the wall and writing cryptic references to the

Companion Cube at the Aperture Science enrichment center- you cannot verify that the other person

ever reads the message. The Network Layer is the layer that uses IP addresses. Most of what we call

"routing" occurs at the network layer - that is,network traffic is routed from one network to another at this

layer, allowing for inter-network (as opposed to intra-network) communication.

Transport (Layer 4)

At the Transport layer, the Network layer's packets are sorted and organized into "segments." This is

different from the idea of packets in the Network layer in one fundamental way: the segments of data over

the Transport layer contain information on the connection and the transmission of data. The Transport

layer removes the uncertainty of "throwing the message in the bottle" that we experience over the Network

layer by attaching to segments (which are basically continued packets) information about the state of a

connection. Thus, the Transport layer uses the LLC sub-layer of the Data Link layer to establish

connections between hosts. The protocols that are typically associated with the Transport layer are:


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TCP: Connection-Oriented, reliable - unlike the "message in the bottle," or "hidden Companion

Cube reference," it can verify that a segment or packet reaches the location, or note failure

UDP: Connectionless, unreliable - it is like a "smarter" message in the bottle service; it makes a

best-effort delivery but does not establish a connection or verify receipt

Session (Layer 5)

The Session layer is the layer that initiates and terminates the transport layer connection-oriented

services . While the Session layer is not widely used by protocols, it is important in that it is responsible for

managing the connections that we value and that the Transport layer provides. In other words, the Session

layer is like the GLaDOS of the transport layer, just like GLaDOS tells the robots what to do and promises

them eternal damnation in case of insubordination, the Session layer also bosses the Transport layer

around.

Presentation (Layer 6)

The Presentation layer translates the segments of information from the Transport layer into data that can be

used at the Application layer. It is like the C3-PO of the OSI model. It is something of an intermediary

between the network node's processing area and the network node's actual networking area - it can

interpret the segments or packets it receives and change them into "data formats" that we all know

and that the PC can recognize.

Application (Layer 7)

This is the top of our cake, utilizes the layers below it, and includes the functions that we are most familiar

with - the end-user application protocols such as FTP and HTTP, the vital services like DHCP and DNS,

and several obscure applications. This is where the sockets are defined. The Application layer does indeed

cover a wide variety of protocols and services, but don't let this overwhelm you. In general, when trying to

decide if a service or protocol is an application level one, ask: "Does this facilitate networking, or does

networking facilitate the service?" If the answer is the latter, you know it is an Application layer service.

Conclusion

The OSI model permeates the theoretical foundation of all networking hardware, software, and standards. It

is the common denominator of networking (at least as far as the Network+ exam is concerned) and will

reappear in just about any discussion of any networking topic. How can you expect to survive the daily

IT department's water cooler conversations without knowing about the OSI model? So, be sure to keep theOSI model in the back of your head and continue to study it! Your reputation among the noble workers of

your company's help desk depends upon it!

The Network+ exam will test you on your ability to differentiate between and recognize the roles of various

pieces of networking equipment. For each piece of equipment, you can generally be expected to know its

function, place in the OSI model, and what differentiates it from similar equipment.


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The Equipment

Hub: A hub, at the most basic level, is a dumb device that operates at the Physical layer of the OSI

model. A hub forwards all signals it receives to all connected network devices . Think of a hub as a

drunk when he speaks, he speaks to all around him, even if he really only means to speak with one

person.

Switch: Because the hub is something of a drunk, it can be an inefficient (think about the excess traffic

created) and unsecure device. Imagine if you wish to send sensitive credit card information over the network

do you really want every node to receive your electronic signal? To alleviate this, the switch was

developed. A switch operates at the Data Link layer of the OSI model. It uses the MAC sub-layer to

forward the relevant frames of information only to the intended recipient. Messages can still be

broadcast, but this is only an option and not the normal condition. Unlike the drunken hub, the switch can

speak softly to one person at a time or announce to the crowd. The Network+ exam tends to test you on this

difference between a hub and switch, so keep it fresh in your mind.

Bridge: A bridgealso operates at the Data Link layer (aka Layer 2) and is used to connect two (similar or

dissimilar) physical network segments together, forming a larger inter-network. It can forward packets or

reject them based on their destination (MAC) address. Note: The connected network segments must have

same network ID.

Router: The routeroperates at the Network layer of the OSI Model and is used to forward packets across

network segments to reach a certain destination address. Do not be confused between a router and a

bridge a bridge simply forwards packets or frames based on their destination address from one connected

network segment to another. A router can determine where a packet should be sent to given its final

destination (IP address). Usually, routers forward packets to other routers, but sometimes routers also

forward to other pieces of network equipment. A router is usually used to connect a home computer to analways-on Internet connection through the home network. To appreciate what a router really does, run

tracert to your favorite website and see how many steps (hops) are involved in getting from your computer to

the web server in question.

Gateway: A gatewayis any device that serves to interface with other networks using dissimilar

protocols . For example, a gateway might interface between a home network and the Internet or between a

NetBIOS network and an IPX/SPX network. A gateway operates in any of the seven OSI layers.

WAP: A Wireless Access Pointis a device that allows wireless devices to access and to communicate

with the network. It acts as a bridge between the wired, traditional network and other wireless

devices.Alternatively, it can act as a bridge between wireless devices and another, linked WAP. It typically

operates in the Network layer of the OSI model as a sort of router/bridge/switch combination. Note that most

WAP devices direct traffic by MAC address, making them switched.


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NIC: A Network Interface Cardis a device that allows a node to connect to the network, typically in the

form of a computer card(PCI/ISA), but also in the form of an external (think USB) device. It can either

be wired and connect to a traditional, wired network, or wireless, and connect to a WAP.

Applying the Knowledge

So now that you know a bit about some networking equipment, lets end with a few review questions thatapply your knowledge.

1. Which of the following devices operate at the Application layer of the OSI model?

A. Hub

B. Switched Hub

C. Router

D. Gateway

E. Bridge

2. You have been asked to implement a network design that incorporates a star topology and is safe from

packet sniffing (other nodes receiving network traffic not directed towards them). In addition, the network

will connect to other networks, including the Internet. Which of the following is not recommended for such a

setup?

A. Switch

B. CAT5 Cabling

C. Hub

D. Router

E. Gateway

Answers

1. The gateway operates at the Application layer of the OSI model , so the answer is D.

2. Because a hub is not immune to such sniffing, as it broadcasts all traffic, the hub would be a terrible

choice for that setup. The answer is C.

We continue now with more networking equipment that you will be expected to know on the Network+

examination. Remember, the exam likes to test on the differences between pieces of equipment as well

as their specific application and place in the OSI model.

Networking Equipment - I


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Equipment

CSU/DSU: A CSU/DSU (Channel Service Unit/Data Service Unit) is a special type of bridge that operates

between the WAN (wide) and LAN (local) networks. It is typically found in devices such as cable

modems, which are not modems in the true sense of the word, but rather, converters from one digital signal

to another. CSU/DSU devices operate in the physical layer of the OSI model.

Modem: A modem (short for modulator demodulator) acts like a sort of CSU/DSU between digital/analog

networks. That is, a modem can translate a physical analog signal to a digital one, and vice-versa. It

typically acts as the intermediary between the analog phone system and digital networks. Modems

operate in the physical layer of the OSI model.

ISDN Adapter: ISDN is a somewhat archaic technology that allows connection via a special digital phone

line. An ISDN Adapter is a CSU/DSU for ISDN connections.

Firewall: A firewall is a device that can filter traffic coming into and out of a network. There are different

types of firewalls that will be tested on the Network+ exam:

Packet Filtering This firewall operates at the network layer of the OSI model, and filters traffic based on

the headers (destination/source) of the individual packets.

Circuit Level Circuit level firewalls filter traffic based on whether or not a session has been established

between the destination and source using TCP handshaking. You can think of a circuit level firewall as

a protective father who will not let his daughter date a boy until he gets to know him. In a similar way,

circuit level firewalls regulate traffic based on whether or not a trusted connection has been established.

These operate in the Session layer of the OSI model.

Application Level Application level firewalls inspect the contents of packets, rather than the

source/destination or connection between the two. Application level firewalls are similar to proxies in that

they operate and regulate between two segments of the network. Remember that an Application Level

firewall operates in the 7th layer of the OSI model (Application Layer) and can inspect the actual

contents of packets.

Stateful Inspection This firewall combines the circuit level and the application level firewall

techniques and is most commonly employed today. It assures the connection (session) between the two

parties is valid (like the circuit level firewall) and inspects packets from this connection to assure the packets

are not malicious (application level). So, the stateful inspection firewall operates in the network, session,and application layers of the OSI model.

Proxy: Proxy Servers operate at the Application layer of the OSI model and serve as filters of client-Internet

traffic. Instead of establishing direct connections between the clients and servers on the Internet,

clients connect to the proxy server, which can filter their request and then forward it to the Internet.

The information sent back is first filtered and then sent back to the client. In this way, a proxy server is

something like the propaganda office of an oppressive government that only presents to its citizens


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information that has gone through the office. The citizens never directly know what is going on, but instead,

what the government (the proxy server) has told them.

And Now for Some Quick Review

So, you should now have a command of all of the tested Network+ equipment. Below are a few questions

that should help stretch your mind a bit.

1. You have a small network connected to the Internet via phone line. Which of the following pieces of

equipment will you need?

a. CSU/DSU

b. Modem

c. ISDN Adapter

d. Bridge

e. Token Ring

2. A client reports that he is unable to connect to a few pages on the Internet, but can connect to almost all

others. Which of the following would prevent him from connecting to these pages?

a. Gateway

b. Router

c. Firewall

d. Proxy Server

e. All of the Above

Answers

1. B A modem modulates/demodulates signals between analog (phone) networks and digital (local area)

networks.

2. D Only the Proxy Server is able to filter individual pages in this way.

Networking Equipment - II

Contents

1 Understanding Frame Types, Especially Ethernet

2 Remembering the Ancestors
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3 Ethernets Entrance

4 Considerations with Ethernet

5 Ethernet Media Table

Understanding Frame Types, Especially Ethernet

Frame technologies are the medium between the physical electric signals and the higher-level logical

packets that drive networking technology. Through the years, we have seen a number of prominent frame

technologies.

Ethernet (802.3) is the frame technology standard that drives most networks today and probably the one

that you are most familiar with. Understanding Ethernet is a key to doing well on the Network+ exam, yet

there is actually not much information that you need to know about Ethernet. Instead, it is more important

that you understand how Ethernet works and the methods it employs in controlling traffic on the wire.

Remember that Ethernet is not a protocol as it operates at the Data Link layer of the OSI model.

Remembering the Ancestors

Before you can understand (and appreciate) Ethernet, it is important to backtrack a bit through the

predecessors of the Ethernet standard.

Typically, when networks are illustrated to laypeople, they are demonstrated as computers that appear to

be linked or daisy-chained to each other. This in fact was one of the earliest networking concepts, the bus

topology. That topology is inexorably linked to the 802.4 Token Bus standard, which defined the way in

which data would move across a token bus network. The standard stipulates that data would be treated like

a token that is, data would move through the network, passing from one node to the next until it reached

its destination. You can imagine some of the problems incurred with this for example, for a frame to travel

across the network, it would have to pass through every node between two communicating nodes. This

mode of communication made impossible the idea of information privacy; in addition, the bus technology is

infamous for the large amount of traffic produced. Dont forget that bus networks require terminators

on the ends on networks to end token travel.

The token ring (802.5), though an improvement on the bus design was only a slight improvement at best. In

the ring formulation, a token still had to be passed from node to node the only difference was that in

the token ring, there was no need for terminators necessarily, but in practice, very few ring networks literally

daisy-chain all of their nodes together. In fact, in many cases, the terminators are still employed. Still, the

ring was promoted as an improvement to the bus standard and a competitor to the rising Ethernet standard.

Ethernets Entrance

Yet, in the end, Ethernet prevailed. The key difference between Ethernet and the aforementioned two

standards was that Ethernet featured a seemingly counter-intuitive and problematic approach to handling

network traffic. In the Ethernet standard, traffic is not passed on a token. Instead, information is sent

almost haphazardly along the wire without regard to the status of other packets. In the token formulation, the

transfer of information can be schematically controlled because the passing of tokens implies that no

collisions occur. Ethernet, in contrast, features a system called CSMA/CD (Carrier Sense Multiple Access

with Collision Detection) that allows Ethernet to automatically detect and fix collisions in frame

communication. The basic principle behind this system can be conveyed in three steps:
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Determine if frame is ready for transmission (if wire is idle); wait until it becomes open

Send frame

Run collision detection procedure if collision occurs

Note About How Ethernet Works: Notice that there is no passing of tokens through nodes in the

Ethernet standard. So, it is very possible that collisions occur. If they do occur, Ethernet simply waits a

random back off period before reattempting transmission. After too many failures, the attempts stop and

the transmission itself is deemed a failure.

Also be aware: Ethernet has a feature called promiscuous mode in which nodes can receive all frames of

information and not just those passed along to those specific computers. This can be defeated by using

switching.

Now, critics of the time charged that the Ethernet system was inefficient, that failing to prevent collisions

would create excess network traffic, and that the Ethernet standard would be inherently slow in nature. All

of these concerns however proved to be unnecessary as the Ethernet standard is still dominant today and

has been since the early 1990s.

Considerations with Ethernet

As with any networking technology, Ethernet has special facets and features you must take into account

when troubleshooting it and dealing with it. One of the most important features of Ethernet today is the

ability to auto-negotiate network speed and duplex mode. Duplex mode refers to whether the traffic is

one-way (talk or listen) or two-way (talk and listen). Half duplex is akin to a one-way radio. A node can

transmit or receieve, but not do both at the same time. Full duplex allows for two-way communication, a

node can both transmit and receive at the same time. Auto-negotiation allows Ethernet devices to determinewhich mode to use. In addition, Ethernet speeds vary depending on medium and the router or gateway

employed; below is a table of Ethernet media and information you should know concerning them.

Ethernet Media Table

Name/Max Length of Cable Type Speed Use

10Base5 / 500 m.

Special coaxial cable, needs

vampire taps (cut into wire to

read), SHARED MEDIUM

(similar to bus)

10

Mbps

Oldest technology and media; rarely

employed today

10Base2 (ThinNet) / 185 m. Coaxial cable with BNCconnector. SHARED MEDIUM

10Mbps

Also old and rarely used, remember

that it requires special circular BNCconnector, similar to cable TV

connector

10BaseT / 100 m.

Twisted Pair wire with

EXCLUSIVE MEDIA (connected

to hubs rather than to other

nodes), RJ-45

10

Mbps

Used RJ-45 connectors (look like

large phone line connector)

100BaseTX (Fast

Ethernet) / 100 m.

Twisted pair wire, EXCLUSIVE

MEDIA, RJ-45

100

Mbps

An improvement on speed of

10BaseT, capable of auto-


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negotiation of speed

1000BaseT (Gigabit

Ethernet) / 100 m.

Twisted pair wire, EXCLUSIVE

MEDIA, RJ-45

1000

MbpsAnother speed improvement

Faster Speed/Other media

Ethernet (10GBASE-SR,

10GBASE-CX4, etc) / 2000+

m.

Uses next-generation fiber optic

cabling to achieve 10+ Gbps

speeds

10+

Gbps

Another speed improvement and

change in connectors, cabling

Note for the exam: You may see options such as 100BaseFX this simply means it is the same as

100BaseTX, but with a fiber optic connection (media) and an SC or ST connector.

Understanding Wireless

Contents

1 Understanding Wireless

2 General Wireless Info 3 Some Review

4 Answers

Understanding Wireless

The Network+ exam is becoming increasingly focused on wireless technology, so it is in your best interest to

learn all of the current wireless standards and implementations. As with almost everything you must learn for

the Network+ exam, it is crucial that you learn the differences between the standards/implementations

and not just their features. Exam questions typically deal with which one to implement, not what this

implementation does. Read and study accordingly.

IrDA (Infrared Data)

IrDA technology allows for communication over network through infrared beams. Infrared (a specturm of

light) does not pass through solid objects, so a direct and clear path is essential for correct IrDA

operation. IrDA typically operates at speeds around 16-25Mbps, but is known to operate at faster speeds

with specialized equipment. It is a rather uncommon wireless networking technology given its inability to

transmit signals where light is blocked. To do this, a lower frequency radio signal is necessary.

Bluetooth

Bluetooth (802.15.1) technology has received a lot of buzz lately, but it is basically a short-range wireless

technology designed to allow for connectivity between portable consumer wireless devices and

Bluetooth enabled wireless access points. Because of the relatively weak and low-frequency radio signal

employed, Bluetooth is typically limited to a 20-35ft. access range. It is therefore usually limited to

applications involving those portable consumer devices and not LAN technology, the most common

application of Wi-Fi.
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Wireless Fidelity (Wi-Fi)

Wi-Fi technology has really taken off in the last few years; it is probably almost as commonly known by its

IEEE name, 802.11(letter). It is a technology that utilizes low-frequency (2.4 and 5GHz.), mid-powered

radio waves to transmit data across wireless networks. While 5 GHz has a higher theoretical throughput,2.4 GHz tends to have a better range. There exist many flavors of the 802.11 standard; they differ

primarily in speed and typical usage. These flavors are listed in a convenient table below:

Name-

StandardSpeed (Mbps) Usage

802.11a 54 5GHz band; outdated; used for LAN networking in businesses; expensive

802.11b 11 Cheaper 2.4GHz mode;

802.11g 54/108Cross between A and B flavors; 2.4GHz at fast speeds. Also offers

backwards compatibility

802.11n 150/300/450/600 Works at either 2.4 GHz or 5 GHz

General Wireless Info

One of the major factors or considerations that many companies think about before employing wireless

technology is its somewhat high cost, though it is falling as time goes by. Still, cost is a major

consideration. Wireless networks are also subject to interference from microwaves, phones, and other

radio devices. Wireless networks are compatible with Ethernet using a MAC bridge that translates wireless

frames into Ethernet frames.

Most wireless networks today connect using a sort of wireless Star topology that is, in many setups,

wireless devices all connect to a single wireless access point. Wireless traffic can be (but is notnecessarily) switched, so information is not easily sniffed from a wireless network. However, Wi-Fi

LANs have become somewhat notorious for their relative insecurities in terms of ease of access. Wi-Fi

LANs are by default accessible without any sort of authentication and therefore vulnerable to different

types of attacks and of course, mooching (wardriving). In addition, the original wireless encryption, Wired

Equivalent Privacy WEP is considered weak by todays standards and should not be used if at all possible.

WEP was replaced by Wi-Fi Protected Access WPA which uses TKIP to encrypt data. WPA was further

improved upon with WPA2, which uses AES to encrypt data. WPA2 should always be used when possible.

Wireless networks can also operate in ad-hoc mode, meaning that nodes can, if they so incline, connect

to each other individually in a sort of mesh scheme. This adds redundancy but makes management of

such a network almost impossible.

Some Review

1. Which of the following IEEE standards specifies Wi-Fi networking?

a. 802.3

b. 802.5c


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c. 802.5d

d. 802.11

e. 802.21

2. You have a large (500+ user) network and wish to link some nodes (laptops) to the network wirelessly,

while leaving most connected to existing hardware. Which of the following would be the most appropriate

setup?

a. Connect the hubs and laptops in a wireless ring topology

b. Connect the laptops to the mainframe using 802.3 10BaseT

c. Employ ad-hoc mode between laptops

d. Employ a star topology, connecting the laptops to a WAP

e. Connect the laptops using IrDA

3. Which of the following is not a valid concern associated with Wi-Fi?

a. War driving

b. Limited signal range

c. Compatibility issues with Ethernet standard

d. Cost of Wi-Fi equipment

e. Interference

Answers

1. 802.11 defines Wi-Fi networking, so the answer is D.

2. The best choice is D, because it allows your network to retain the existing physical topology while allowing

the new nodes (laptops) to connect wirelessly in a manageable and scalable way.

3. All of the mentioned are concerns with the exception of C, which is absurd because Wi-Fi was specificallydesigned to work with 802.3 using a bridge.

TCP/IP Addressing and IPv6

1 TCP/IP Addressing and IPv6
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2 The IPv4 Address

3 IPv6

4 Practicing What You Preach

5 Answers

TCP/IP Addressing and IPv6

The Network+ exam will contain a few questions on TCP/IP IPv4 addressing, which is a fairly simple

subject matter to master and will earn you some easy points. It is therefore recommended that you

understand what an IP address is and how the numbering of the IP address reveals network information.

The IPv4 Address

An IPv4 Address, often shortened to IP Address, is a numeric identifier of a network node that uniquely

identifies that node either on a LAN or on the wider Internet. Therefore, if two nodes on a network use the

same IP address, a conflict will occur as the IP address reflects a one-to-one relationship between

hardware and logical address. As a result, neither of the two nodes with duplicate addresses will receive full

communications.

The IP address is 32-bit number comprised of four octets ranging from 0 to 255, or 256 numbers

(numbers that range from 0 to 2^8-1, hence the term "octet"). Given this, there are a limited number of IP

addresses at maximum, 256^4 or 4,294,967,296. This number is inflated because certain IP addresses

are reserved or unavailable. Given the rate of growth that the Internet is currently experiencing, it is widely

recognized that 4 billion IP addresses will not be enough to compensate for all of the nodes of the world. It is

for this reason that many advocate changing to IPv6, which is 128 bits and utilizes hexadecimal (base 16),

rather than octal (base 8), numbers. IPv6 will be covered briefly later. What you should know is that although

IPv6 is superior in many ways to IPv4, IPv4 is the most commonly used protocol for now and so is the one

tested on the Network+ exam.

The IP address is comprised of two parts: the netid and the hostid. The netid indicates the network that

a node is on while the hostid indicates the actual, specific node. The number of octets dedicated to the netid

varies based on the first number of the network. Actually, that first number tells you quite a bit. The first

number determines the size (Class) of the network and therefore both the number of octets dedicated to the

"netid" and the number dedicated the "hostid". Below is a table of the first octet numbers and information

about their classes:

The Class-Octet Table

ClassFirst Octet

RangeExample Default Subnet Typical Application

A (netid . hostid . hostid .

hostid)1-126 17.14.22.211 255.0.0.0 University Network System

B (netid. netid. hostid.

hostid)128-191 143.144.1.1 255.255.0.0

Corporate System or Hospital

Network

C (netid. netid. netid.

hostid)192-223 204.213.288.222 255.255.255.0

Small Business, Home Internet

Connection

If you noticed, there is a column above for Default Subnet. Subnetting is a feature of TCP/IP whereby

networks can be subdivided, creating logical networks within a given network. This allows one, in effect, to
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create multiple networks on a single IP network by routing the subnets (nodes connect via a default gateway

which can find the router) necessary for communication with other logical networks.

Note that there are some reserved IP address ranges:

IP Range And Purpose

Range Purpose

127.0.0.0 127.255.255.255 Loopback (returns the node that requests it)

10.0.0.0 10.255.255.255 Private Network (Class A)

172.16.0.0 - 172.31.255.255 Private Network (Class B )

192.168.0.0 192.168.255.255 Private Network (Class C)

(255.255.255.255 is reserved as a Broadcast address, which sends information to all nodes on the

same network)

Often times, a connection (through a router) to the Internet may be shared by multiple computers, which

raises the question: What IP addresses do the computers that connect to the Internet through the router

take? Actually, they are assigned a private IP address in one of the above reserved ranges for

communication within the LAN; external communication is all channeled through the single wide IP

address. This is called Network Address Translation and dont worry about it for now well cover it later.

IPv6

IPv6 is an emerging technology that is coming into networking as the IPv4 address space is being

exhausted. It differs from IPv4 in several important ways, first it is 128 bits instead of 32 bits, it is written in

hexadecimal instead of decimal, and bytes are seperated by colons instead of periods.

With those considerations we can write an IPv6 address as such:

0000:0000:0000:1aff:1923:ab00:0000:22a1:3712:0000:0000:0000:acc2:32aa:8eff:bf00

Obviously this is an unwieldy number for networking so the authors of IPv6 gave us some shortcuts to help

us out. First a double colon can be used to symbolize long strings of zeroes in an address but only once for

each address. For example, the previous address could be written as:

::1aff:1923:ab00:0000:22a1:3712:0000:0000:0000:acc2:32aa:8eff:bf00

or

0000:0000:0000:1aff:1923:ab00:0000:22a1:3712::acc2:32aa:8eff:bf00

but not

::1aff:1923:ab00:0000:22a1:3712::acc2:32aa:8eff:bf00

as the computer would have no way of knowing how long each block of zeroes actually is thus rendering the

address unreadable.


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Additionaly consecutive zeroes can be expressed as a single 0. So our previous address would be correctly

expressed as:

::1aff:1923:ab0:0:22a1:3712:0:0:0:acc2:32aa:8eff:bf0

While still far longer than an IPv4 address you can see that this is much more manageable.

The authors did us another favor and created a new loopback address. Rather than losing an entire range of

addresses as they did in IPv4, the IPv6 loopback is ::1.

This should cover everything you need to know about IPv6 for the Network+ exam. However, as a network

technician you should remember that it is an emerging technology, at some point you will have to work with

it, and you should keep up with, and eventually know it as well as IPv4.

Practicing What You Preach

Now, here are a few sample problems that should help you jog your knowledge on IP addressing.

1. A network has nodes on IPs ranging from 143.144.12.0 to 143.144.12.222. The router on this network is

at 143.144.12.1. The IP address of Node A is 143.144.12.27. What is the default gateway for Node A?

A. 255.255.0.0

B. 127.0.0.1

C. 143.144.12.27

D. 143.144.12.26

E. 143.144.12.1

2. Which of the following is a valid public Class A IP address?

A. 127.143.22.22

B. 10.41.55.16

C. 0.4.0.3

D. 123.2.15.15

E. 166.44.13.12

3. Which of the following is a not a possible subnet mask?

A. 255.0.0.0


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B. 255.255.0.0

C. 255.255.252.0

D. 255.255.255.0

E. 255.255.255.255

4. Which of the following is a valid IPv4 address?

A. 4:AC:AD:34

B. 266.144.13.3

C. 244.233.12.1

D. 10:0:0:1

E. 10:0:0:A

5. You install and configure a new computer. In doing this, you add the new computer to your IP-based

network and assign it an IP address. After restarting, you notice that the connection to the network is

sporadic; in addition, another user calls you and complains that his network connection is not functioning.

What is the most likely explanation?

A. You configured the wrong default gateway

B. You configured a duplicate IP address

C. You used a unique IP address

D. You configured a duplicate subnet address

E. You used a unique subnet address

Answers

1. The default gateway for a node is the same as the router that connects the node to the other subnets on

the entire LAN; therefore, because the router is 143.144.12.1, the default gateway is 143.144.12.1. The

answer is (E)

2. Review the table to see the ranges for valid Class A IP addresses. Note that although ([[Image:|user

posted image]] is in the range 1-126, 10.x.x.x is reserved for private Class A networks. Therefore (D) is the

correct answer.

3. All of the above are possible except for (E), which is reserved as the broadcast address. Note that answer

C is a possible subnet address.


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4. IP addresses are four octets (numbers within 0-255, normally 1-254) separated by periods. The only

choice that satisfies this is choice C

5. After adding the new PC to the network, neither the new PC nor the complaining users PC is receiving full

service. The only way that the new PC would affect the users PC is if the new PC is using a duplicate IP

address, which would deny service to either. Therefore the answer is B.

Protocols of TCP/IP Protocol Suite

Contents

1 TCP/IP stack

2 Data Link

3 Network

4 Transport

5 Application

TCP/IP stack

The TCP/IP stack has more than just the TCP and IP protocols; in fact, it is home to the most pervasive and

prevalent protocols that cover many layers of the OSI model. The Network+ exam will test you on your

knowledge of the protocols of the TCP/IP stack (suite), including information on the layers and uses

of the individual protocols. Below is a list of the exam-tested protocols, arranged by place in the OSI

model.

Data Link

Because no protocols operate at the Physical layer of the OSI model, we begin at the Data Link layer.

The ARP (Address Resolution) protocol operates at the Network layer and is used to translate logical IP

addresses into Data Link (Physical) MAC (Media Access Control) addresses. It is basically the

translator between Layers 2 and 3.

The RARP (Reverse ARP) is similar to the ARP protocol, but translates MAC addresses into IP addresses.

Network

The ubiquitous IP protocol allows for much of the routing capabilities of the Internet; specifically, it allows

for the connectionless transfer of packets. Most of the functionality concerning the IP protocol is actually

centered on the concept of addressing, or assigning unique logical identifiers to nodes.

ICMP (Internet Control Message Protocol) Is a connectionless protocolthat allows you to use functions

such as ping to check if a route is available to a certain network node. More generally, ICMP is used to

manage control messages.
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IGMP (Internet Group Management Protocol) is used to add, delete, and modify members of multicast

groups. A multicast is a packet sent to more than one user but not all users distinguished, of course, from

the broadcast, which is a message to all users.

The RIP (Routing Information Protocol) allows for the routing of internal (and also some Internet) traffic

and adapting to changes in network structure.

Transport

TCP (Transmission Control Protocol) is the connection-oriented protocol that allows for reliable data

transfer and receipt of delivery between two network nodes. One of the unique features of TCP is the

concept of a port, or an opening into a node in which data is sent and/or received. Higher-level protocols

(especially Application layer protocols) depend on TCP ports to allow outside nodes to communicate with

specific services.A port number is always between 1 and 65536, inclusive.

UDP(User Datagram Protocol) is the connectionless equivalent of TCP. In a Connectionless protocol, a

session is not created before sending the data, therefore, there is no guarantee of data delivery.

UDP is usually seen as an unreliable protocol because of this but does facilitate several higher-level

protocols and also utilizes the 1-65536 port system. Make sure you understand that there is a distinctionthen between TCP and UDP ports namely, the protocol employed.

Application

The Network+ exam will not test you very much on the individual application layer protocols, but you will

need to know simple information such as their purpose and port number. Remember that when it is said that

a service operates on a certain port, it doesnt mean that the service cannot operate on a different port; it just

means that is the default.

HTTP (Hypertext Transfer Protocol) is the protocol that facilitates transfer of data via the world wide web.

Typically, data is transferred in the form of pages, or HTML markup. HTTP operates on TCP 80.

HTTPS (Secure HTTP) uses TCP 443 to securely transfer HTTP data via SSL, or Secure Socket Layer.

Sites that require increased security, such as an online merchant, use HTTPS to protect user information.

(Note: TLS is the newer SSL)

FTP (File Transfer Protocol) operates on TCP ports 20(data) /21(transmission control). It is used in simple

file transfers from one node to another without any security (transferred in cleartext).

SFTP (Secure FTP) is a version of FTP that uses SSH to transfer data securely, thus using whichever port

SSH uses. Port 22 for those who can't figure it out.

TFTP (Trivial FTP) is a UDP version of FTP that utilizes UDP port 69. It is called trivial because it is

relatively unreliable and inefficient and so is more often used for inter-network communication (along

routers) than in real node-to-node file transfers.

Telnet (Telecommunications Network) is used to remotely connect to a node. All communications with telnet

are in cleartext (even the password for authentication) and should not be used in sensitive situations. It is

called terminal emulation software because the remote terminal is available upon connection. Telnet

operates on TCP 23.


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SSH (Secure Shell) is a secure replacement of Telnet. Telnet transfers information in plain or clear text,

but SSH allows terminal emulation in cipher text, which equates to enhanced and increased security. SSH

operates on TCP 22.

NNTP (Network News Transfer Protocol) is a protocol used by client and server software to carry USENET

(newsgroup) postings back and forth over a TCP/IP network. NNTP operates on TCP port 119.

LDAP (Lightweight Directory Access Protocol) is a Directory Services protocol that basically allows a

server to act as a central directory for client nodes. A famous implementation of LDAP is Microsofts Active

Directory (Domain). LDAP operates on TCP and UDP 389.

NTP (Network Time Protocol) allows for synchronizing network time with a server. NTP operates on UDP

123.

POP3 (Post Office Protocol) is the mailbox protocol of the Internet and allows users to download mail from a

mail server. The server will hold onto your mail until you access it. Once you try to access it, your client

software will download all of your incoming mail and wipe it from the server. POP3 operates on TCP 110.

IMAP4 (The Internet Message Access Protocol) is a slightly better version of the mailbox protocol. IMAP4

allows for server-based repositories of sent mail and other specialized folders. Basically, when using IMAP4

instead of POP3 as your incoming mailprotocol, you download very minimal information to your local

machine and when you want to access actual incoming mail, you are pulling this directly from the mail

server. This allows you to access your mail from virtually anywhere (like yahoo mail). IMAP4 operates on

TCP 143.

SMTP (Simple Mail Transfer Protocol) is the postman of the Internet. It allows for mail to be sent. You

would use this in conjunction with POP3 or IMAP4 to be able to send/receive mail. If you do not define

SMTP (usually is, though), you will only be able to receive mail. SMTP operates on TCP 25.

DNS(Domain Name System) Resolves easy to read domain names such as google.com into computer

readable IP addresses such as 72.14.204.147 DNS operates on UDP 53

SNMP (Simple Network Management Protocol) A protocol for managing devices on IP networks, such as

modems, switches, routers, or printers.Works on UDP 161

NAT & ICS

Contents

1 NAT & ICS

2 How Network Address Translation Works

3 Considerations

4 ICS (Internet Connection Sharing)

5 Quick Review

6 Answers:

NAT & ICS
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The ICS-enabled PC can then share its connection with other Windows computers, acting as an NAT

device. In addition, the ICS-enabled PC can automatically assign IP addresses through DHCP, a feature

covered in a different article.

Quick Review

1. A user complains that he cannot access his office computer through Remote Desktop. He iscertain that he has entered the correct hostname to connect to and that Remote Desktop is

listening on the office computer. What is the most likely explanation?

a. Remote Desktop has encountered an illegal exception

b. He needs to enable ICS on the remote PC

c. He needs to enable NAT on the remote PC

d. NAT on the office router/gateway is blocking his request to his office PC

e. His office router/gateway is down

2. Which of the following is not a reason that NAT is currently employed?

a. Exhaustion of IPv4 addresses

b. Ability to block incoming traffic from remote hosts

c. Ability to share an Internet connection

d. To minimize costs (for having extra IP addresses)

e. Allows automatic assignment of IPv4 addresses

Answers:

1. The user cannot access his PC because his PC is most likely behind an NAT-enabled device, which

would prevent incoming traffic because no port would be available by default. The answer is D.

2. DHCP allows automatic assignment of IPv4 addresses; this is not a feature of NAT. The answer is E.

DHCP, Port Forwarding, and DMZ Hosts

Contents

1 DHCP, Port Forwarding, and DMZ Hosts

2 DHCP

3 Port Forwarding
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4 DMZ Host

5 Applying the Knowledge

6 Answers

DHCP, Port Forwarding, and DMZ Hosts

You will, as a Network administrator, probably deal with DHCP, port forwarding, and the DMZ more often

than you may like. These technologies are classically associated with NAT technology; so, many

modern networks utilize them to provide various network services and greater security.

DHCP

Dynamic Host Configuration Protocol, or DHCP, is the service that allows for the dynamic (often called

auto-magical) IP configuration of client nodes on a given network. Typically (in most home or small-office

networks), DHCP is employed over manual configuration. In larger networks, DHCP can be very

advantageous because it allows network administrators to "kick back and relax" while addresses are auto-

magically assigned through a DHCP server. However sometimes a manual configuration may be more

desirable so that administrators know which computers correspond to which IP address that is, so that theassignments are permanent.

DHCP works on a release/renew system. When an address is requested and assigned, it is actually

leased to the requesting node for a given period of time. After half of the lease time has expired, the

requesting node will automatically request a renewal of the IP to the original DHCP server. In most cases,

the server will help the client renew the assigned IP address. If the server that the IP was originally assigned

from (the DHCP server that assigned the IP) is unavailable after around 87.5% of the lease time has

expired, the client will send a broadcast to all network nodes asking for an IP address. When the lease

expires, however, the node will lose the IP address. Note that DHCP operates in a client/server rationale,

so a DHCP client requests an IP address from a willing DHCP server. DHCP assigns the:

IP address

Subnet mask

Default gateway

Microsoft Windows, Linux, and Macintosh all offer built-in DHCP server functionality.

Port Forwarding

Most routers today offer a feature called port forwarding that works in conjunction with NAT (Network

Address Translation) to provide openings for incoming traffic to internal network nodes. A typical

application of port forwarding is network configuration for a file sharing program. The file sharing program on

node 192.168.1.4 may need a specific port open to accept incoming traffic for example, lets say TCP

4444. Because of NAT, requests on TCP 4444 will not be handled because the traffic is being directed to the

router, which does not have any service operating on TCP 4444. However, the router can be configured to

forward requests on port TCP 4444 to 192.168.1.4, which can handle the requests on TCP 4444, thusallowing for the incoming traffic to be handled on that port. The general formulation for port forwarding is:

Port Request on (TCP/UDP) (Port Number)Forwards to(Internal IP Address)

DMZ Host

A DMZ (Demilitarized Zone) host is a special (security) feature in many modern routers. A DMZ host is

basically a catch-all host for requests on non-configured ports. For example, in the previous example,
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lets say port forwarding is not configured, but a DMZ host on 192.168.1.33 is. Then, the request to the

router on TCP 4444 (because it is not forwarded) will be automatically sent to 192.168.1.33:4444. There are

two main benefits associated with DMZ hosts.

1. Port forwarding doesnt have to be configured for each individual service (though it is generally a

BAD idea to setup an ordinary PC as a DMZ host)

2. As a security feature (quite the opposite of number 1), so that all of the suspicious (non-port-

forwarded) traffic can be directed to a single sanitized host

Applying the Knowledge

1. Which of the following technologies allows a PC to forward incoming requests on certain ports to

specific computers?

a. NAT

b. ICS

c. DMZ

d. Port Forwarding

e. DHCP

2. A user complains that he cannot connect to the network. You ask him for his IP information and

he says that his IP is manually assigned. Which of the following could be eliminated as cause of the

problem?

a. The media may be faulty, severed, or incorrectly connected

b. His IP address, subnet mask, or default gateway may be wrong

c. His network card may not be functioning correctly

d. The DHCP server is down

e. The default gateway is down

Answers

1. Port forwarding allows for the forwarding of specific port requests to specific computers. The answer is D.

2. Because the IP address is manually assigned, the DHCP server could not be an issue because it is notbeing utilized. All of the other choices, however unlikely, are possibilities. The answer is D.

TCP/IP Troubleshooting Tools

TCP/IP is a wonderful protocol suite; it comprises almost all of the functionality and the core services that

make possible for the Internet and its applications. However, with great power come many problems; so,


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knowledge of TCP/IP troubleshooting will be necessary in your networking-related career and especially in

your ability to pass the Network+ exam. In fact, you will probably encounter around four or five

questions on TCP/IP troubleshooting alone on the Network+ exam.

Your knowledge of TCP/IP troubleshooting depends on your command of TCP/IP tool usage. Many of the

following tools are used in typical troubleshooting operations, and almost all of them can be used to eitheridentify or eliminate a potential problem in a troubleshooting situation. We will go over general network

troubleshooting in more detail in later articles.

To give an example of the way TCP/IP troubleshooting tools can help, consider the common tool ping.

Ping operates over the ICMP protocol (using ICMP Echo Request and Echo response) to attempt to

contact a host given some kind of unique identifier (hostname, domain, IP, etc.). If it is successful, it will

return a reply from that IP address; if it is unsuccessful, it will inform you that the destination could not be

reached. Why is this useful? Suppose you are trying to determine why you are unable to access the

companys remote email server through Outlook. The problem could stem from a number of issues,

including

The computer is not properly configured for the internal network (media problems, TCP/IP

configuration issues, router is down, etc.)

The Internet connection is down

There is an issue in connecting to the email server at the Application or Connection layers (maybe

he is connecting to the wrong port, NAT issues, email server is rejecting connections)

The remote host is down or is unavailable in general (IP connection issues)

Obviously, these are only four of many possibilities, but they are four possibilities that can be further

investigated through Ping. For example, to ping your router would indicate to you if your router or network

connection is down, or if the problem lies at the remote host level. This kind of step-by-step, process of

elimination process is how most troubleshooting takes place. Some other tools include:

Tracert: Traces the connection path to a remote host, step-by-step. Allows you to see where

the connection is lost for example, sometimes a connection to a remote host may stop at an ISP

router, at which point you can determine that the issue is a WAN problem.

Netstat: Depending on the parameters, gives varying degrees of information about TCP/IP

connections and protocols. Examples include information such as all connections and listening

ports, routing table etc

Ipconfig: Displays IP configuration information with the switch (/all), which includes IP address,

subnet mask, and default gateway. Ipconfig can also be used to force a DHCP release or renew

operation, using the switches /release and /renew

ifconfig: Displays IP configuration information in a UNIX environment. ifconfig

interface_namecan also be used to display the IP configuration information for a specific interface

Winipcfg - the GUI-based Windows 9x-era ipconfig tool

ARP Returns the MAC address that maps from a given IP address

RARP Returns the IP address that maps to a given MAC address


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Nslookup Used to troubleshoot DNS issues; can be used to find an IP given a DNS name

There are of course other TCP/IP tools, but they will be covered in other sections (i.e. NetBios). The most

important things to remember about the above TCP/IP tools are not the details of their functionality, but

rather, remember the troubleshooting operations that they are associated with. For example, if you

read about some sort of DNS issue, you should immediately think Nslookup before considering other tools.

Quick Practice

1. A user reports that he is unable to connect to your companys network. The user is running

Windows 98. Which of the following commands would be most appropriate to run?

a. ipconfig

b. winipcfg

c. winipconf

d. ipconf

2. Which of the following commands can be used to renew a DHCP leased address?

a. Dhcp /renew

b. Dhcp /lease?extend

c. Ipconfig /renew

d. Ipconfig /extend

3. Which utility shows active connections on a host?

a. Netstat

b. Telnet

c. Tracert

d. ICMP

4. Which of the following uses ICMP echo requests to determine if a remote host is available?

a. Ping

b. Telnet

c. Arp

d. ICMP

Answers


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1. Winipcfg is the equivalent of ipconfig for Windows 9x machines. The answer is B

2. Ipconfig with the switch /renew can renew a DHCP lease; the answer is C

3. Netstat shows active connections on a host. The answer is A

4. Ping uses ICMP echo requests to check if a host is reachable. The answer is A

NetBIOS

Contents

1 NetBIOS

2 NetBIOS Naming

3 NetBIOS Sessions

4 Quick Review

5 Answers:

NetBIOS

NetBIOS, or Network Basic Input/Output System, allows for session-layer communication on the OSI

model. NetBIOS is primarily concerned with two functions: naming and starting/stopping NetBIOS

sessions. Since NetBIOS is not actually a networking protocol (it's an API) it is not routable and therefore

nodes are only visible to other nodes within the same subnet. It also provides for an unreliable NetBIOS

datagram service which is rarely utilized these days (and probably not on your Network+ exam). So, we will

cover the two basic aspects of NetBIOS: naming and sessions.

NetBIOS Naming

NetBIOS names are 16 bytes in length but usually consist of 15 characters, with the last being reserved for

special purposes. You are probably familiar with the 15 character limit if you have any experiences with

naming PCs almost all operating systems require the PC name to be 15 characters in length or less. All

NetBIOS names resolve to one or more IP addresses. If a NetBIOS name resolves to a single IP address

(that is, if the relationship is said to be one-to-one), it is called a Unique Name. If the name

resolves to more than one computer, it is said to be a Group Name. The Network+ exam tests you

specifically on NetBIOS naming in Microsoft Windows networks. Name resolution is an important feature of

a NetBIOS network; after all, how would you know which NetBIOS names correspond to given IP

addresses? NetBIOS name resolution is handled through several means.

A broadcast is simply a request to all nodes on a network to resolve a given name. Think of it as calling

out someone in a crowd. Yelling Is Anthony Parks here? may result in someone who identifies himself as

Mr. Parks to turn around and proclaim, Yes, I am Anthony! Alternatively, perhaps nobody in the crowd

bears that name, and the request may be forwarded to other people. Similarly, in a NetBIOS network,

broadcasts are sent to all nodes, asking for a response if a computer recognizes the name as its own.

However, broadcasts can be cumbersome and boggle down a busy network imagine the amount of noise

created if everyone is asking for someone in a crowded room! To resolve this problem, several centralized

NetBIOS name resolution services exist, including:
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