Network+ 2005 In Depth (P19) ppt

To converse,VoIP callers can use either a traditional telephone, which uses analog signals, a telephone spe-cially designed for TCP/IP transmission, or a computer equipped with a microph

Voice signals can be carried over TCP/IP networks in a variety of configurations To converse,VoIP callers can use either a traditional telephone, which uses analog signals, a telephone spe-cially designed for TCP/IP transmission, or a computer equipped with a microphone, speaker,and VoIP client software And on any VoIP network, a mix of these three types of clients ispossible.

If a VoIP caller uses a traditional telephone, signals issued by the telephone must be converted to ital form before being transmitted on a TCP/IP-based network.This conversion can be accomplished

dig-in several ways One way is by usdig-ing an adapter card withdig-in a computer workstation The traditionaltelephone line connects to an RJ-11 port on the adapter card The adapter card, along with its devicedrivers and software on the computer, converts the voice signals to IP packets, and then issues thepackets to the data network

A second way to achieve this conversion is by connecting the traditional telephone to a switch

or router capable of accepting traditional voice signals, converting them into packets, then

issuing the packets to a data network One example of such a switch is a digital PBX or, more commonly, an IP-PBX (PBX stands for private branch exchange, which is the term used to

describe a telephone switch used to connect calls within a private organization.) In general, anIP-PBX is a private switch that accepts and interprets both analog and digital voice signals.Thus, it can connect with both traditional PSTN lines and data networks An IP-PBX trans-mits and receives IP-based voice signals to and from other network connectivity devices, such

as routers or gateways

In a third scenario, the traditional telephone connects to an analog PBX, which then connects

to a voice-data gateway In this case, the gateway connects the traditional telephone circuitswith a TCP/IP network (such as the Internet or a private WAN) The gateway digitizes incom-ing analog voice signals, compresses the data, assembles the data into packets, and then issuesthe packets to the packet-switched network This process relies on special VoIP compressionand digitizing protocols In addition, to translate between the PSTN and VoIP networks,gateways follow special VoIP signaling protocols A discussion of these protocols is beyond thescope of this book However, if you choose to specialize in VoIP networking, you need to under-stand such protocols thoroughly When transferring calls from a packet-switched network to

a circuit-switched network (for example, if you call your home telephone number from youroffice’s IP telephone), a gateway performs the same functions in the reverse order

Figure 11-16 depicts the different ways traditional telephones can be used to access a VoIP network

Rather than traditional telephones, most new VoIP installations use IP telephones (or IP phones), which transmit and receive only digital signals When a caller uses an IP telephone,

his voice is immediately digitized and issued from the telephone to the network in packet form

To communicate on the network, each IP telephone must have a unique IP address, just as anyclient connected to the network has a unique IP address The IP telephone looks like a tradi-tional touch-tone phone, but connects to an RJ-45 wall jack, like a computer workstation Then,its connection may pass through a connectivity device, such as a hub or switch, before reach-ing the IP-PBX An IP-PBX may contain its own voice-data gateway, or it may connect to a

separate voice-data gateway, which is then connected to the network backbone Figure 11-17illustrates different ways IP telephones can connect with a data network.

IP telephones act much like traditional telephones For example, they feature speed-dialing,call hold, transfer, and forwarding buttons, conference calling, voice mail access, speakers andmicrophones, and an LCD screen that displays caller ID and call hold information They come

in both mobile and wire-bound styles More sophisticated IP telephones offer features not able with traditional telephones Because IP telephones are essentially network clients, likeworkstations, the number and types of customized features that can be programmed for use withthese phones is limitless Makers of IP telephones include Alcatel, Avaya, Cisco, Mitel, NEC,Nortel, and Siemens In the United States, an IP telephone can cost between $150 and $750.Rather than using traditional telephones or IP telephones, a third option is to use a computer

avail-programmed to act like an IP telephone, otherwise known as a softphone Softphones and IP

tele-phones provide the same calling functions; they simply connect to the network and deliver services

in different manners Before it can be used as a softphone, a computer must meet minimum ware requirements (which any new workstation purchased at an electronics store would likely meet),

hard-be installed with an IP telephony client, and communicate with a digital telephone switch In tion, softphone computers must have a sound card capable of full-duplex transmission, so that both

addi-Chapter 11 513

VOIP (VOICE OVER IP)

FIGURE 11-16 Accessing a VoIP network from traditional telephones

the caller and the called party can speak at the same time Finally, a softphone also requires a phone and speakers or a headset.

micro-Despite all the advantages to using VoIP, it is more difficult to transmit voice signals over apacket-switched network than data signals, which are designed for packet-switched transmis-sion First, more so than data transmissions, voice conversations can easily be distorted by aconnection’s quality of service When you talk with your friend, you need to hear his syllables

in the order in which he mouthed them, and preferably, without delay Therefore, packets rying voice signals must be received in the same order in which they were issued and reassem-

car-FIGURE 11-17 Accessing a VoIP network from IP phones

bled quickly (In contrast, data packets do not necessarily have to be received in the same order

in which they were transmitted, because the destination node will sort the information when

it arrives.) Also, voice transmissions are subject to distortion if the connection becomes toonoisy In general, to prevent delays, disorder, and distortion, a voice connection requires morededicated bandwidth than a data connection

When VoIP is carried via the Internet, it is often called Internet telephony But not all VoIP

calls are carried over the Internet In fact, VoIP over private lines is an effective and ical method of completing calls between two locations within an organization And becausethe line is private, its network congestion can be easily controlled, thus resulting in better soundquality than an Internet telephone call can provide But given the Internet’s breadth and lowcost, it is appealing to consider the Internet for carrying conversations that we currently trans-mit over the PSTN

econom-Chapter Summary

◆ Subnetting separates one network or segment into multiple logically defined ments, or subnets A network administrator might subnet a network to achieve sim-pler troubleshooting, enhanced security, improved performance, and easier networkmanagement

seg-◆ A subnet mask provides clues about the location of network information in an IPaddress Bits in a subnet mask that equal 1 indicate that corresponding bits in an IPaddress contain network information Bits in a subnet mask that equal 0 indicate

that corresponding bits in an IP address contain host information

◆ To create subnets, some of an IP address’s bits that would, by default, represent hostinformation are changed to represent network information instead The change isindicated by a change in the subnet mask’s bits

◆ If you use subnetting on your LAN, only your LAN’s devices need to interpret yourdevices’ subnetting information External routers, such as those on the Internet, payattention to only the network portion of your devices’ IP addresses—not their subnetmasks—when transmitting data to them

◆ A newer variation on traditional subnetting is provided by CIDR (Classless Domain Routing) CIDR offers additional ways of arranging network and host informa-tion in an IP address In CIDR, conventional network class distinctions do not exist

Inter-◆ CIDR allows the creation of supernets, or subnets established by using bits that mally would be reserved for network class information By moving the subnet

nor-boundary to the left, more bits are made available for host information, thus ing the number of usable host addresses on a subnetted network

increas-◆ Gateways facilitate communication between different subnets Because one device on thenetwork cannot send data directly to a device on another subnet, a gateway (usually in theform of a router interface) must intercede and hand off the information

Chapter 11 515

CHAPTER SUMMARY

◆ Every device on a TCP/IP-based network has a default gateway, the gateway that firstinterprets its outbound requests to other subnets, and then interprets its inbound requestsfrom other subnets.

◆ Internet gateways maintain default routes to known addresses to expedite data transfer.The gateways that make up the Internet backbone are called core gateways

◆ NAT (Network Address Translation) allows a network administrator to “hide”

IP addresses assigned to nodes on a private network In NAT, gateways assign missions valid Internet IP addresses when the transmission is sent to the Internet

trans-◆ ICS (Internet Connection Sharing) is a service, included with Windows 98, Me,

2000, and 32-bit versions of XP operating systems, that allows a network of puters to share a single Internet connection through an ICS host computer

com-◆ Many private organizations use browser-based services for communication among rized employees of the organization over an intranet For communication with authorizedpersonnel both from the organization and external to the organization, they may use anextranet

autho-◆ All Internet mail services rely on the same principles of mail delivery, storage, and pickup,though they may use different types of software to accomplish these functions

◆ Mail client software can communicate with various types of mail server software,because the TCP/IP Application layer protocols used for this communication arestandard

◆ SMTP (Simple Mail Transfer Protocol) is responsible for moving messages fromone e-mail server to another over TCP/IP-based networks SMTP operates throughport 25, with requests to receive mail and send mail going through that port on theSMTP server SMTP is used in conjunction with either POP or IMAP MIMEoperates over SMTP to enable mail messages to contain non-ASCII content, such

as graphics, audio, video, and binary files Most modern e-mail clients supportMIME encoding

◆ POP (Post Office Protocol) is a mail retrieval protocol The most current and monly used version of POP is called POP3 Using POP3, messages are downloadedfrom the mail server to a client workstation each time the user retrieves messages

com-◆ IMAP (Internet Message Access Protocol) is another mail retrieval protocol Itsmost current version is IMAP4 IMAP4 differs from POP3 in that it allows users tostore messages on the mail server, rather than always having to download them tothe local machine This is an advantage for users who do not always check mail fromthe same computer

◆ The netstat utility displays TCP/IP statistics and the state of current TCP/IP ponents and connections It also displays ports, which can signal whether services areusing the correct ports

com-◆ The nbtstat utility provides information about NetBIOS names and their addresses

If you know the NetBIOS name of a workstation, you can use nbtstat to determinethe workstation’s IP address

◆ The nslookup utility allows you to look up the DNS host name of a network node

by specifying the node’s IP address, or vice versa Nslookup is useful for

trou-bleshooting host configuration and DNS resolution problems

◆ The dig utility, like nslookup, queries the network’s DNS database to return mation about a host given its IP address, or vice versa In its simplest form, or whenused with one of its many switches, dig provides more information than nslookup

infor-◆ The whois utility allows you to obtain DNS registration information for a level domain

second-◆ The traceroute utility, known as tracert on Windows-based systems, uses ICMP totrace the path from one networked node to another, identifying all intermediate

hops between the two nodes This utility is useful for determining router or subnetconnectivity problems

◆ Typing ipconfigat the command prompt of a system running Windows NT, 2000,

XP, or Server 2003 reveals the TCP/IP settings for that computer

◆ You can view TCP/IP settings on a system that uses the Windows 9x or Me ing system by typing winipcfgat the command prompt

operat-◆ Ifconfig is the utility that establishes and allows management of TCP/IP settings on

a UNIX-type of system

◆ VoIP (voice over IP) is the use of packet-switched TCP/IP-based networks to carryvoice signals An organization may use VoIP to save money on telephone calls, cen-tralize management of voice and data services, or take advantage of customizable callfeatures

◆ Many types of clients and network designs are available with VoIP networks Clientscan be traditional telephones, IP telephones, or softphones (a computer running

telephony software and connected to a microphone and headphones)

◆ Analog VoIP clients may connect to traditional PBXs (private telephone switches),which then connect to a voice-data gateway that digitizes call information DigitalVoIP clients typically connect to a digital PBX or a router with VoIP capabilities

Key Terms

ANDing—A logical process of combining bits In ANDing, a bit with a value of 1 plus another

bit with a value of 1 results in a 1 A bit with a value of 0 plus any other bit results in a 0

CIDR (Classless Inter-domain Routing)—An IP addressing and subnetting method in

which network and host information is manipulated without adhering to the limitationsimposed by traditional network class distinctions CIDR is also known as classless routing orsupernetting Older routing protocols, such as RIP, are not capable of interpreting CIDRaddressing schemes

Chapter 11 517

KEY TERMS

CIDR block—In CIDR notation, the number of bits used for an extended network prefix.

For example, the CIDR block for 199.34.89.0/22 is /22

CIDR notation—In CIDR, a method of denoting network IDs and their subnet boundaries.

Slash notation takes the form of the network ID followed by a /, followed by the number of bits thatare used for the extended network prefix

classful addressing—An IP addressing convention that adheres to network class distinctions, in

which the first 8 bits of a Class A address, the first 16 bits of a Class B address, and the first 24 bits

of a Class C address are used for network information

Classless Inter-domain Routing—See CIDR.

classless routing—See CIDR.

convergence—The use of packet-switched networks to carry data, plus video and voice

sig-nals

core gateway—A gateway that operates on the Internet backbone.

default gateway—The gateway that first interprets a device’s outbound requests, and then

interprets its inbound requests to and from other subnets In a Postal Service analogy, thedefault gateway is similar to a local post office

default router—See default gateway.

dig (domain information groper)—A TCP/IP utility that queries the DNS database and

provides information about a host given its IP address or vice versa Dig is similar to thenslookup utility, but provides more information, even in its simplest form, than nslookup can

digital PBX—See IP-PBX.

domain information groper—See dig.

extended network prefix—The combination of an IP address’s network ID and subnet

infor-mation By interpreting the address’s extended network prefix, a device can determine the net to which an address belongs

sub-extranet—A network that uses browser-based services to exchange information within an

orga-nization and with certain, authorized users outside of that orgaorga-nization.

HTML (Hypertext Markup Language)—The language that defines formatting standards for

Web documents

Hypertext Markup Language—See HTML.

ICS (Internet Connection Sharing)—A service provided with Windows 98, Me, 2000 and

32-bit versions of XP operating systems that allows one computer, the ICS host, to share itsInternet connection with other computers on the same network

ICS host—On a network using the Microsoft Internet Connection Sharing service, the

com-puter whose Internet connection other comcom-puters share The ICS host must contain two work interfaces: one that connects to the Internet and one that connects to the LAN

net-ifconfig—A utility that establishes and allows management of TCP/IP settings on

UNIX-type of systems

IMAP (Internet Message Access Protocol)—A mail retrieval protocol that improves on the

shortcomings of POP The single biggest advantage IMAP4 has relative to POP is that itallows users to store messages on the mail server, rather than always having to download them

to the local machine The most current version of IMAP is version 4 (IMAP4)

IMAP4 (Internet Message Protocol, version 4)—The most commonly used form of the

Internet Message Access Protocol (IMAP)

Internet Connection Sharing—See ICS.

Internet Message Access Protocol—See IMAP.

Internet Message Access Protocol, version 4—See IMAP4.

Internet telephony—The provision of telephone service over the Internet.

intranet—A network or part of a network that uses browser-based services to exchange

infor-mation within an enterprise Intranets may be contained within a LAN or may be accessiblevia a WAN or the Internet

IP-PBX—A private switch that accepts and interprets both analog and digital voice signals

(although some IP-PBXs do not accept analog lines) It can connect with both traditionalPSTN lines and data networks An IP-PBX transmits and receives IP-based voice signals toand from other network connectivity devices, such as a router or gateway

IP phone—See IP telephone.

IP telephone—A telephone used for VoIP on a TCP/IP-based network IP telephones are

designed to transmit and receive only digital signals

IP telephony—See Voice over IP.

MIME (Multipurpose Internet Mail Extensions)—A standard for encoding and

interpret-ing binary files, images, video, and non-ASCII character sets within an e-mail message

Multipurpose Internet Mail Extensions—See MIME.

NAT (Network Address Translation)—A technique in which IP addresses used on a private

network are assigned a public IP address by a gateway when accessing a public network

nbtstat—A TCP/IP troubleshooting utility that provides information about NetBIOS names

and their addresses If you know the NetBIOS name of a workstation, you can use nbtstat todetermine its IP address

Chapter 11 519

KEY TERMS

netstat—A TCP/IP troubleshooting utility that displays statistics and the state of current

TCP/IP connections It also displays ports, which can signal whether services are using the rect ports

cor-Network Address Translation—See NAT.

network number—See network ID.

network prefix—See network ID.

nslookup—A TCP/IP utility that allows you to look up the DNS host name of a network node

by specifying its IP address, or vice versa This ability is useful for verifying that a host is figured correctly and for troubleshooting DNS resolution problems

con-PBX (private branch exchange)—A telephone switch used to connect calls within a private

organization

POP (Post Office Protocol)—An Application layer protocol used to retrieve messages from

a mail server When a client retrieves mail via POP, messages previously stored on the mailserver are downloaded to the client’s workstation, and then deleted from the mail server

POP3 (Post Office Protocol, version 3)—The most commonly used form of the Post Office

Protocol

Post Office Protocol—See POP.

Post Office Protocol, version 3—See POP3.

private branch exchange – See PBX.

Simple Mail Transfer Protocol—See SMTP.

slash notation—See CIDR notation.

SMTP (Simple Mail Transfer Protocol)—The Application layer TCP/IP subprotocol

respon-sible for moving messages from one e-mail server to another

softphone—A computer programmed to act like an IP telephone Softphones present the caller

with a graphical representation of a telephone dial pad and can connect to a network via a LAN,WAN, PPP dial-up connection, or leased line

supernet—A type of subnet that is created using bits that normally would be reserved for

net-work class information—by moving the subnet boundary to the left

supernet mask—A 32-bit number that, when combined with a device’s IP address, indicates

the kind of supernet to which the device belongs

supernetting—See CIDR.

toll bypass—A cost-savings benefit that results from organizations completing long-distance

telephone calls over their packet-switched networks, thus bypassing tolls charged by commoncarriers on comparable PSTN calls

traceroute (tracert)—A TCP/IP troubleshooting utility that uses ICMP to trace the path from

one networked node to another, identifying all intermediate hops between the two nodes.Traceroute is useful for determining router or subnet connectivity problems On Windows-based systems, the utility is known as tracert

Voice over IP (VoIP)—The provision of telephone service over a packet-switched network

running the TCP/IP protocol suite One form of VoIP (pronounced “voyp”) is Internet phony, though VoIP is frequently used over private networks to circumvent long-distance tollcharges

tele-VoIP – See voice over IP.

winipcfg—The TCP/IP configuration and management utility for use with Windows 9x and

Me systems Winipcfg differs from ipconfig in that it supplies a graphical user interface

whois—The utility that allows you to query ICANN’s DNS registration database and find the

4. The _ utility displays TCP/IP statistics and detailsabout TCP/IP components and connections on a host.

9. True or false? The Post Office Protocol is a Transport layer protocol used to retrievemessages from a mail server

10. True or false? Voice over IP is the use of packet-switched networks and the TCP/IPprotocol to transmit voice conversations

11. To calculate a host’s network ID given its IP address and subnet mask, you follow alogical process of combining bits known as _

12. A network or part of a network that uses browser-based services to exchange tion within an enterprise is known as a(n) _

informa-13. The utility that allows you to query the DNS registration database and obtain mation about a domain name is called _

infor-14. The _ utility uses ICMP to trace the path from one worked node to another, identifying all intermediate hops between the two nodes

net-15. On Unix-type systems, the _ utility allows you to ify TCP/IP settings for a network interface, release and renew DHCP-assignedaddresses, or simply check the status of your machine’s TCP/IP settings

mod-Troubleshooting Network Problems

Chapter 12

After reading this chapter and completing the exercises, you will be able to:

■ Describe the steps involved in an effective troubleshooting

probably spends more time fixing network problems than designing or upgrading a network.Some breakdowns (such as an overtaxed processor) come with plenty of warning, but others(such as a hard disk controller failure) can strike instantly.

The best defense against problems is prevention Just as you maintain your car regularly, youshould monitor the health of your network regularly Of course, even the most well-monitorednetwork will sometimes experience unexpected problems For example, a utility companycould dig a new hole for its cable and accidentally cut your dedicated link to the Internet Insuch a situation, your network can go from perfect to disastrous performance in an instant Inthis chapter, you learn how to diagnose and solve network problems in a logical, step-by-stepfashion, using a variety of tools

Troubleshooting Methodology

Successful troubleshooters proceed logically and methodically This section introduces a basictroubleshooting methodology, leading you through a series of general problem-solving steps.These steps follow the recommendations specified in CompTIA’s Network+ exam objectives.Bear in mind that experience in your network environment may prompt you to follow thesteps in a different order or to skip certain steps entirely For example, if you know that onesegment of your network is poorly cabled, you may try replacing a section of cable in that area

to solve a connectivity problem before attempting to verify the physical and logical integrity ofthe workstation’s NIC In general, however, it is best to follow each step in the order shown.Such a logical approach can save you from undertaking wasteful, time-consuming efforts such

as unnecessary software or hardware replacements

Steps for troubleshooting network problems are as follows:

1. Identify the symptoms and potential causes Record what you learn from people orsystems that alerted you to the problem and keep that documentation handy

2. Identify the affected area Are users across the entire network experiencing the lem at all times? Or, is the problem limited to a specific geographic area of the net-work, to a specific demographic group of users, or to a particular period of time? Areall of the symptoms related to a single problem, or are you dealing with multipleproblems?

prob-NET+

4.9

3. Establish what has changed Recent hardware or software changes may be causing thesymptoms.

4. Select the most probable cause To find the probable cause, you may need to completethe following:

a. Verify user competency

b. Recreate the problem, and ensure that you can reproduce it reliably

c. Verify the physical integrity of the network connection (such as cable tions, NIC installations, and power to devices), starting at the affected nodesand moving outward toward the backbone

connec-d. Verify the logical integrity of the network connection (such as addressing, tocol bindings, software installations, and so on)

pro-5. Implement an action plan and solution and be prepared for all potential effects Forexample, if you have to reassign IP addresses, how will the change of an IP address on

a server affect its clients? Or, in another case, if you upgrade the type of client ware used on a workstation, how will that affect a user’s daily routine?

soft-6. Test the result Has your solution been implemented successfully?

7. Identify the results and effects of the solution

8. Document the solution and process Make sure that both you and your colleagues

understand the cause of the problem and how you solved it This information should

be kept in a centrally available repository, such as an online database

Chapter 12 525

TROUBLESHOOTING METHODOLOGY

In addition to the organized method of troubleshooting described in this section, agood, general rule for troubleshooting can be stated as follows: Pay attention to theobvious! Although some questions may seem too simple to bother asking, don’t dis-count them You can often save much time by checking cable connections first Everynetworking professional can tell a story about spending half a day trying to figure outwhy a computer wouldn’t connect to the network, only to discover that the networkcable was not plugged into the wall jack or the device’s NIC

TIP

Identify the Symptoms and Potential Causes

When troubleshooting a network problem, your first step is to identify the specific symptoms

of the problem After you identify the problem’s symptoms, you can begin to deduce its cause.For example, suppose you have identified a user’s inability to access a network drive as a symp-tom At that point, you can list several potential causes, including a faulty NIC, cable, hub, orrouter; an incorrect client software configuration; a server failure; or a user error On the otherhand, you can probably rule out a power failure, a printer failure, an Internet connectivity fail-ure, an e-mail server failure, and a host of other problems

NET+

4.9

NET+

4.9

Answering the following questions may help you identify symptoms of a network lem that aren’t immediately obvious:

prob-◆ Is access to the network affected?

◆ Is network performance affected?

◆ Are data or programs affected? Or are both affected?

◆ Are only certain network services (such as printing) affected?

◆ If programs are affected, does the problem include one local application, one worked application, or multiple networked applications?

net-◆ What specific error messages do users report?

◆ Is one user or are multiple users affected?

◆ Do the symptoms manifest themselves consistently?

One danger in troubleshooting technical problems is jumping to conclusions about the toms For example, you might field 12 questions from users one morning about a problem print-ing to the network printer in the Facilities Department You might have already determinedthat the problem is an addressing conflict with the printer and be in the last stages of resolv-ing the problem Minutes later, when a 13th caller says, “I’m having problems printing,” youmight immediately conclude that she is another Facilities staff member and that her inability

symp-to print results from the same printer addressing problem In fact, this user may be in theAdministration Department, and her inability to print could represent a symptom of a largernetwork problem

Take time to pay attention to the users, system and network behaviors, and any error messages.Treat each symptom as unique (but potentially related to others) In this way, you avoid therisk of ignoring problems or—even worse—causing more problems

Take note of the error messages reported by users If you aren’t near the users, askthem to read the messages to you directly off their screens or, better yet, print thescreens that contain the error messages (On some computers, pressing the PrintScreen button—which is sometimes labeled “Print Scrn” or “PrtSc”—will issue a copy

of what’s on the screen to the computer’s clipboard, after which it can be printed orsaved as a file On other computers, you can use the Shift+Print Screen or Alt+PrintScreen keystroke combinations.) Keep a record of these error messages along withyour other troubleshooting notes for that problem

TIP

Identify the Affected Area

After you have identified the problem’s symptoms, you should determine whether the problemaffects only a certain group of users or certain areas of the organization, or if the problem occurs

NET+

4.9