CompTIA A+ Essentials 220-601: Networks
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Lesson 1. Course Introduction
In this course, you will learn about basic networking concepts and networking models such as peer-to-peer and client/server. You will become more familiar with such things as Local Area Network (LAN) and Bluetooth as you learn more about network technologies. Finally, you will look at different network architectures, such as Ethernet and Token Ring.Lesson 2. Network Protocols and Hardware
After completing this lesson, you should be able to:
- Identify the fundamental principles of networks
Before we discuss networking protocols and hardware, let's examine a few critical concepts.
Addressing
Addressing is the assignment of IP addresses to hosts on a network. There are two categories of IP addresses: public and private. An Internet Service Provider (ISP) provides public IP addresses used over the Internet. You have to purchase public IP addresses from an ISP. Private IP addresses are available free of charge and are used on a LAN. You cannot use private IP addresses over the Internet.
Bandwidth
Bandwidth is the rate at which information travels from one location to another over a channel. Bandwidth is typically measured in Megabits per second (Mbps), Kilobits per second (Kbps), or bits per second (bps). The amount of information that can be sent at any time depends on the available bandwidth at that time — the higher the bandwidth, the greater the amount of information that can be passed from one location to another.
Status Indicators
Status indicators are used to determine whether a network device such as a Network Interface Card (NIC) or a switch is working properly. You can diagnose network device problems with status indicators. A NIC has two indicator lights: a link indicator and an activity indicator that provide information on the status of the link and on network activity, respectively. A switch has indicator lights that show whether the device is working properly.
Full- and Half-Duplex
A full-duplex connection can send and receive data over two separate circuits at the same time. A half-duplex connection has a single circuit; it can either send data or receive data, but cannot perform both actions at the same time. If an application requires two-way communication, you should use a full-duplex connection. A full-duplex connection will let the application perform more efficiently.
Network architecture is a collective term that denotes a collection of protocols, topologies, and access methods. Examples of network architectures include the Ethernet and Token Ring topologies. The pages that follow provide more detail about these architectures.
Ethernet is a group of standards used in a LAN. The naming standard is the same for different Ethernet types. The first number of each standard indicates the transmission speed in Mbps, the middle section indicates the signaling type, and the last section indicates the transmission medium.
For example, in a 100BaseTX model, the "100" indicates that the network can transmit data at 100 Mbps. "Base" indicates that the network uses the baseband transmission method — meaning only one signal is sent over the network medium at a time. "TX" indicates that a twisted-pair cable is used as the network medium. T can also indicate twisted-pair cable, and F, FL, FX, LX, and SX indicate fiber optic cable. In the Ethernet standards 10Base2 and 10Base5, the "2" indicates thinnet coaxial cable and "5" indicates thicknet coaxial cable.
Standard Ethernet implementations include 10Base2, 10Base5, 10BaseT, and 10BaseF. Fast Ethernet runs at a maximum of 100 Mbps; its implementations include 100BaseT, 100BaseTX, and 100BaseFX. Gigabit Ethernet runs at a maximum of 1000 Mbps; its implementations include 1000BaseT, 1000BaseCX, and 1000BaseFX.
Token Ring networks can be of Type 1 or Type 3. Type 1 networks normally use STP cables and operate at 4 or 16 Mbps. Type 3 networks use UTP cables; they also operate at 4 or 16 Mbps.
A network is an interconnection of computers that use the same or different network protocols. A protocol is a set of rules that determine how computers communicate over a network. Protocols are grouped according to their functions.
Some commonly-used protocols include:
- TCP/IP
- NWLINK IPX/SPX (Internetwork Packet Exchange/Sequence Packet Exchange)
- NETBEUI/NetBIOS (NetBIOS Extended User Interface/Network Basic Input/Output System)
TCP/IP is a standard set of rules used for communication in large networks. TCP/IP is managed through two different hierarchical structures. First is the IP address hierarchy, which uniquely identifies a host such as a computer, printer, or router in a network. Second is the TCP hierarchy, a transport-level protocol responsible for providing reliable data delivery over the network.
TCP/IP is included with Windows 9x, Windows ME, Windows NT, Windows 2000, and Windows XP. Communication over the Internet requires TCP/IP.
Three major fields have to be configured for TCP/IP: the IP address, the subnet mask, and the default gateway. These are described on the pages that follow.
An IP address is a 32-bit number that is a combination of four 8-bit numbers known as octets. This 32-bit number is in the abc.abc.abc.abc format, where abc is a decimal number in the range of 0 to 255. An example of an IP address is 202.10.100.1.
A network administrator can assign an IP address manually, or a computer can be configured to attain its IP address automatically from a server on the network by using the Dynamic Host Configuration Protocol (DHCP).
The subnet mask divides a large TCP/IP network into smaller networks. A subnet defines all computers that have a common network prefix. IP addresses have a network section that identifies the network to which the computer belongs and a node section that identifies the network address of the computer. A network can be categorized into classes, with each class being allowed to use a defined set of IP addresses.
Class A
Class A uses IP addresses ranging from 1.0.0.0 to 126.255.255.255. The first octet, 1 to 126, identifies the network as a Class A network. The rest of the address identifies the host on the network. Class A networks can have a maximum of 126 networks, and each network can have 16,777,214 hosts, by using the default subnet mask 255.0.0.0.
Class B
Class B uses IP addresses ranging from 128.0.0.0 to 191.255.255.255. The first two octets, 128.0 to 191.255, identify the network as a Class B network. The rest of the address identifies the host on the network. Class B networks can have a maximum of 65,534 networks, and each network can have 65,534 hosts, by using the default subnet mask of 255.255.0.0.
Class C
Class C uses IP addresses ranging from 192.0.0.0 to 223.255.255.255. The first three octets, 192.255.0 to 223.255.255, identify the network as a Class C network. The rest of the address identifies the host on the network. Class C networks can have a maximum of 2,097,152 networks, and each network can have 254 hosts, by using the default subnet mask of 255.255.255.0.
The default gateway specifies the address of the router to which the host sends all TCP/IP traffic. It also helps send TCP/IP traffic from a source computer to a target computer on a different subnet. Every computer connected in a network has the same default gateway address.
If a network consists of more than one subnet, data can still be sent to a target computer in a different subnet by using a default gateway address. The address of the default gateway is also required if the computer is connected to the Internet.
IPX/SPX is the protocol used on Novell NetWare networks. To support the IPX/SPX protocol, Microsoft created its own version, known as NWLINK. IPX/SPX requires a network number and a frame type setting if possible.
The network number is an 8-digit alphanumeric number that uniquely identifies a network segment of the IPX/SPX network and enables IPX Internetwork routing.
The frame type is usually autodetected. If not detected, the frame type defaults to IEEE 802.2. IPX/SPX is included with Windows 9x, Windows ME, Windows NT, Windows 2000, and Windows XP.
NetBEUI is a modified version of the Network Basic Input/Output System (NetBIOS) developed by Microsoft for Windows networking. The NetBIOS protocol is a name resolution protocol that searches for computers on a LAN by computer name. It is used mostly in Ethernet and token ring networks.
NetBIOS sends a request as a network control block, which contains information such as the request location and the name of the destination host. NetBIOS works in two modes:
- Session mode allows a connection between two computers, transfer of large messages, and error detection and recovery.
- Datagram mode allows the broadcast of messages on the entire LAN.
Whenever there's a need for connecting two or more computers, you require a network. The selected networking model may differ based on your requirements and the number of computers you want to install on the network. There are two basic networking models: peer-to-peer and client/server.
Peer-to-peer
A network that has no dedicated servers, where individual workstations can share data or services with other workstations, is known as a peer-to-peer network. In a peer-to-peer network each computer can function as a client or a server. All computers are considered equal in functionality, and there is no central server controlling the access of resources. Peer-to-peer networks are effective when the total number of participating workstations doesn't exceed 20. As the network grows beyond this size issues such as security, administration, and data backups tend to become problems. A peer-to-peer network architecture is more suitable for small businesses where security isn't a concern.
Client/server
The client/server model uses a network operating system to manage the network and act as a central authority for network resources. In a client/server network, there's at least one centralized server running the network operating system that allows network administrators to control the network. A client or workstation can make requests to the server for resources, and the server can fulfill or reject those requests. This provides a secure and organized network. Windows NT, Windows 2000, and Windows 2003 networks are client/server networks. Windows 2000 and 2003 use domains to provide centralized control of security.
Cables connect two network devices and transfer information between them. Coaxial, twisted pair, fiber optic, and Plenum/PVC cables connect network devices on a LAN.
You can use an RS-232 serial cable, Universal Serial Bus (USB) cable, or an IEEE 1394/FireWire cable to connect two computers directly. An external modem connects to the serial port of a computer with an RS-232 cable.
USB and IEEE 1394/FireWire cables provide serial data transfers. A USB cable has only one pair of wires for data transfer; it provides half-duplex data transmission. RS-232, USB, and IEEE 1394/FireWire cables allow a serial port on one computer to be connected directly to another computer with a null-modem cable, which is a cable with specific pin contacts reversed.
You'll need an adapter to perform the pin reversal required for a direct connection. When one of these adapters is used, it is possible to connect two computers through their serial ports using a standard serial cable without reversing any pin contacts in the cable.
Coaxial cable was the most commonly used cable type in early computer networks. In modern networks coaxial cable has been replaced by UTP, STP, fiber optic, and wireless media.
Coaxial cable is half-duplex; it supports a transmission rate of 10 Mbps, which is considered slow compared to other cable types.
Unshielded Twisted Pair (UTP) cables consist of four pairs of wires with no foil shield. Examples of UTP cables are:
- CAT3 T is used in 10BaseT networks; it supports transmission speeds up to 10 Mbps.
- CAT5 supports transmission speeds up to 100 Mbps, but it has been phased out in favor of Category 5e. It also provides backward-compatibility to the older and much slower 10 Mbps standards.
- CAT6 supports transmission speeds up to 1000 Mbps. While Category 5e also supports speeds of up to 1000 Mbps, Category 6 is recommended for best results. It also provides backward-compatibility to the older and much slower 10 Mbps standards.
Shielded Twisted Pair (STP) cables consist of four pairs of insulated wires with a foil shield wrapped around the wires. STP cable is identical to UTP except for the shielding.
The metallic shield protects the cable from interference caused by fluorescent light fixtures, motors, and other electromagnetic interference (EMI) sources. STP cables can be used in any implementation where UTP cables are used, but are more expensive than UTP. STP is generally preferred only when shielding from EMI is required.
Fiber optic cable can be used with Ethernet networks. It carries digital data and voice signals in the form of modulated pulses of light. There are two types of fiber optic cable:
- Single Mode fiber optic cable has a thin core-diameter of 5 or 10 microns. It uses a laser to transmit one signal at a time. Practical transmission distances for single-mode fiber optic range up to 50 km.
- Multi Mode fiber optic cable has a core-diameter of 50, 62.5, or 100 microns. It transmits multiple signals using a light-emitting diode (LED). Practical transmission distances for multi-mode fiber optic range up to 3,000 km.
Because it does not produce toxic fumes when it burns, Plenum/Polyvinyl Chloride (PVC) cable is used in plenum (air-filled) spaces in buildings, such as ventilation ducts. Non-plenum cables are covered with PVC that produces toxic gas when it burns. Most fire codes require plenum-rated cable in any area that carries breathable air.
Each type of cable requires a specific type of connector for termination.
Standard connectors (SC) and Straight Tip (ST) connectors
Fiber optic NICs usually include an ST or SC connector. ST fiber uses a round-plug style connector, while SC fiber uses a square-block style connector. Fiber optic cable is commercially available either with the same connector at both ends or with an ST connector at one end and an SC connector at the other end.
Lucent Connector (LC) connectors
LC connectors are used with single-mode and multi-mode fiber optic cables. LC connectors use a plastic housing; they provide precise alignment through ceramic ferrules. LC connectors have a locking tab.
Mechanical Transfer-Registered Jack (MT-RJ) connectors
MT-RJ connectors are used with single-mode and multi-mode fiber optic cables. MT-RJ connectors use a plastic housing; they provide precise alignment through metal pins and plastic ferrules. MT-RJ connectors are cheaper than SC and ST connectors, and they support full-duplex communication.
Registered Jack-11 (RJ-11) connectors
RJ-11 connectors are the standard connector for telephone connections. An RJ-11 connector has four wires. It's used to create a connection between telephone-line jacks and analog modems.
Registered Jack-45 (RJ-45) connectors
RJ-45 connectors are similar to RJ-11 connectors but larger. An RJ-45 connector connects both UTP and STP cables to hubs, NICs, and various other twisted-pair networking devices. An RJ-45 connector has eight wires in four pairs. A UTP cable typically has a male RJ-45 connector on each end. These plug into female connectors built into networking devices.
USB and IEEE1394/FireWire connectors
These interfaces support instant networking. Instant networking allows two Windows XP computers to communicate simply by using a FireWire cable and the TCP/IP protocol stack. FireWire supports an end-to-end throughput of over 50 Mbps.
Networking Cables
The important concepts are:
- Coaxial
- The most commonly used cable type in early computer networks, but has been replaced by other media.
- Unshielded Twisted Pair
- Consists of four pairs of wires with no foil shield.
- Shielded Twisted Pair
- Consists of four pairs of insulated wires with a foil shield wrapped around the wires.
- Fiber Optic
- Is available in two types: Single Mode and Multi Mode
- Plenum/ Polyvinyl Chloride
- Does not produce toxic fumes when it burns.
Lesson 3. Network Technologies
After completing this lesson, you should be able to:
- Define various network technologies
LAN-based Internet connectivity can be established in various ways. If it is a small organization, you can use a dial-up connection and then distribute the Internet connectivity among multiple computers. When you need to configure Internet connectivity for a LAN, typically a computer or device is configured to act as a gateway.
The primary task of a gateway is to perform routing between networked computers and the Internet. A gateway is simply responsible for sending and receiving data packets. You can also configure dedicated connections such as ISDN, DSL, or cable-based Internet connectivity for WAN connections.
ISDN is a digital architecture that defines hardware and call-setup schemes for end-to-end connectivity. This technology can carry video, voice, and data for transmission to the specified destination. ISDN uses two separate channels for in-band and out-of-band signaling.
ISDN lines have a faster call setup than LANs because both channels are separate. A dedicated D channel is used for out-of-band signaling. Compared to normal telephone lines, which use the same channel for in-band and out-of-band signals, ISDN is faster.
The three different types of ISDN services are:
- Primary Rate Interface (PRI) — Consists of 23 B channels and one D channel (64 Kbps) in North America and Japan for a total bandwidth that is equivalent to one T1 leased line, or 30 B channels and one D channel in Europe, Australia and most of the rest of the world with the slightly higher capacity E1.
- Basic Rate Interface (BRI) — Consists of two B channels which provide a data transfer speed of 64 Kbps and one D channel which provides the data transfer speed of 16 Kbps.
- Broadband ISDN — Offers transfer rates of up to 633 Mbps and uses coaxial or fiber-optic cables.
Broadband provides high-speed connectivity over the internet. Technologies such as Digital Subscriber Line (DSL), cable, and satellite provide high-speed Internet connectivity.
DSL
DSL describes the broad category of Internet access technologies that use telephone wire to transmit signals to and from the Internet. There are several variants of DSL available in the market. Asynchronous DSL is capable of downstream transfers of 8 Mbps and upstream transfers of 1 Mbps. The other forms of DSL provide speeds from 144 Kbps to 1.5 Mbps downstream and 128 Kbps to 512 Kbps upstream. DSL connections use standard RJ-11 connectors between the modem and the ISP. An advantage of DSL is that the existing UTP telephone cables can be used to connect the DSL modem to an RJ-11 wall socket.
Cable
Cable modem-based Internet connections always use standard coaxial cable to establish a direct connection to the Internet. A cable modem connects to a computer by using an RJ-45 Ethernet cable or a USB cable.
Satellite
Satellite technology can cover large geographic areas because no cables are required for its implementation. The disadvantage of satellite technology is that it is slower than cable, ISDN, or DSL. The satellites and receiving dishes need to be aligned, or the signal will be noisy and weak. A common problem with satellite communication is delay. Signals take time to reach and then return from the satellite. This delay is known as latency. Bad weather also affects communications using satellite technology. There are two types of satellite-based connections: one-way and two-way. One-way uses a dial-up modem and an ISP. In a one-way connection the computer connects to an Indoor Receive Unit (IRU), which connects through a coaxial cable to the satellite dish. A two-way uses two satellites to send and receive information. In a two-way connection, an Indoor Transmit Unit (ITU) is used along with an IRU. A coaxial cable can be used with the IRU, ITU, and satellite dishes.
Dial-up access uses the telephone system to allow communication between computers. Dial-up networking uses analog modems that convert the parallel digital signals generated by a computer into serial analog signals suitable for transmission over telephone wires. Dial-up connections can transmit data at speeds up to 56.6 Kbps.
For dial-up networking, you can use either an internal or external modem. An internal modem is installed inside the computer's system case in an expansion slot on the motherboard. It's equipped with its own interfacing circuitry. An external modem is installed outside the computer. It connects to a serial port of the computer using an RS-232 cable. An external modem uses the interfacing circuitry of the serial port.
Wireless devices connect to the Internet through an access point. Wireless-based Internet connectivity is used in hotels, airports, or restaurants where customers can use the access points to connect to the Internet. This type of Internet connectivity is often a paid service.
There are several wireless specifications:
- The 802.11a wireless standard supports a maximum speed of 54 Mbps at a frequency of 5 GHz.
- The 802.11b wireless standard supports a maximum speed of 11 Mbps at a frequency of 2.4 GHz.
- The 802.11g wireless standard supports a maximum speed of 54 Mbps at a frequency of 2.4 GHz. The 802.11g standard is compatible with the 802.11b standard, ensuring backward compatibility. 802.11g access points can work with 802.11b wireless network adapters and vice-versa.
- The Bluetooth wireless standard supports a maximum speed of 400 Kbps at a frequency of 2.4 GHz.
Bluetooth, defined by the IEEE as standard 802.15, is a wireless network protocol intended to provide convergence between wireless-enabled devices such as computers, printers, keyboards, mice, cellular telephones, and PDAs. Bluetooth is the best wireless communication technology to communicate with multiple devices.
Bluetooth wireless range depends on the class of the Bluetooth device:
- Class I: provides communication with a maximum distance of 100 meters.
- Class II: provides communication with a maximum distance of 10 meters.
- Class III: provides communication at short distance and is rarely used today.
Infrared technology is a wireless technology used to send and receive information by using electromagnetic radiation in the infrared band. Infrared provides relatively short-range communication up to 12 feet with a data transfer rate of less than 4 Mbps.
Infrared is the cheapest wireless technology. Modern laptops come with built-in support for infrared. The Infrared Data Association (IrDA) is the authority that defines protocol standards and specifications for short-range communication using infrared light.
Cellular technology is a radio technology made up of many cells. A transmitter is used to serve these cells, which provide radio coverage over a wide area. Several types of cellular technology can be used, such as Code Division Multiple Access (CDMA) and Time Division Multiple Access (TDMA).
CDMA technology uses wide frequency channels to send messages that are decoded at the receiving end. TDMA technology divides time slots among different users so they can share the same radio frequency.
General Packet Radio Service (GPRS) is a wireless technology used in mobile devices to transfer data. GPRS technology operates at a speed of 115 Kbps. This technology is useful for sending and receiving e-mail and for browsing the Web.
Voice over IP (VoIP) technology is used to carry voice signals over IP telephony. This technology allows you to make voice calls through a broadband Internet connection. VoIP calls costs less than calls made through the Public Switched Telephone Network (PSTN), but VoIP voice quality is reduced.
Networking Technologies
The important concepts are:
- VoIP
- Allows you to make voice calls through a broadband Internet connection
- Infrared
- Used to send and receive information by using electromagnetic radiation
- Dial-Up Access
- Uses the telephone communication system to allow communication between computers
- ISDN
- Uses two separate channels for in-band and out-of-band signaling
Lesson 4. Installing and Configuring Networks
After completing this lesson, you should be able to:
- Install and configure networks
A cable broadband connection provides fast Internet access through coaxial cable. A cable broadband connection is relatively cheaper than other broadband connections. It provides faster Internet download speeds than dial-up access.
To configure cable broadband on your computer, you need a cable modem, usually provided by your ISP. A cable modem is pre-configured; you don't need to perform any additional configurations.
Note: When a router has been used to connect two computers to a single broadband connection, you can use the Web browser running on one of the computers to configure the router.
Configuring a NIC with a Static IP Address
To configure a network interface card (NIC) on a Windows XP computer, attach the NIC to any available PCI slot on the motherboard and install appropriate network card drivers with the Device Manager. Let's examine the steps for configuring a NIC in a Windows XP computer that has a static IP address.
To configure the host IP addresses manually , double-click Internet Protocol (TCP/IP) in the Local Area Connection Properties dialog box.
The Internet Protocol (TCP/IP) Properties dialog box opens. You can assign an IP address to the computer by using dynamic IP address assignment, static assignment, or Automatic Private IP Addressing (APIPA). In a Windows network, the IP address, subnet mask, and default gateway must be specified to configure a host on the network.
Enter the IP address, subnet mask, and default gateway of the computer. We've completed this step for you.
The NIC has been configured with a static IP address.
Windows 98, Windows 2000, and Windows XP support Automatic Private IP Addressing (APIPA). If a client can't communicate with a DHCP server at startup, APIPA enables DHCP clients to automatically configure their IP addresses and subnet masks.
A client configured with APIPA will periodically attempt to locate a DHCP server. Once the DHCP server is found, APIPA is not used.
When a computer uses APIPA, Windows determines the IP address in reverse order. APIPA addresses range from 169.254.0.0 through 169.254.255.255, with a subnet mask of 255.255.0.0.
Wireless access points are used in wireless networks for connecting wireless devices. Each access point supports connections up to a specified distance. In a large wireless LAN, you may have to install a number of wireless access points to establish connectivity.
To configure wireless access points, you should provide the IP address and gateway address in wireless access point settings. You can use wireless access points as a router and a DHCP.
Let's examine the terminology and technology involved with configuring wireless access points.
Wireless Application Protocol
The Wireless Application Protocol (WAP) uses Wireless Markup Language (WML) to format data to fit into smaller displays, such as those found in Personal Communication System (PCS) phones and PDAs. Data is sent in compressed binary packets.
Wireless Transport Layer Security
The Wireless Transport Layer Security (WTLS) is based on the Transport Layer Security (TLS) protocol and derived from the Secure Sockets Layer (SSL) protocol. WTLS provides security for WAP applications in the form of data integrity, privacy, authentication, and Denial-of-Service (DoS) protection. WTLS helps address wireless issues such as limited processing power, memory, and bandwidth. Wireless transactions require strict security measures because of their vulnerability to data interception. WTLS provides an optimized handshake mechanism that allows keys to be changed periodically during a wireless session.
Wired Equivalent Privacy
The Wired Equivalent Privacy (WEP) encrypts data as it is transmitted between a wireless client and the access point. WEP can be used to secure transmissions after authentication. WEP does not provide encryption during authentication, and it allows user credentials to be broadcast in clear text. WEP can be effective when used with other security methods, such as passwords, authentication, Virtual Private Networks (VPN), and encryption of all data transmissions.
Service Set Identifier
A Service Set Identifier (SSID) is a network name that is broadcast in clear text. The SSID identifies the presence of a wireless network to any wireless client that is in range. In secure environments wireless clients can be configured with the SSID for their network, thereby eliminating the need to broadcast the identity and availability of the wireless network. When you configure a wireless access point as a router and a DHCP, you should specify the SSID in the user computers. To ensure the security of the network, you should also change the password while configuring a wireless access point.
Wireless Access Point Technologies
The important concepts are:
- Wireless Application Protocol
- Uses Wireless Markup Language (WML) to format data to fit into smaller displays.
- Wireless Transport Layer Security
- Provides security for WAP applications in the form of data integrity, privacy, authentication, and Denial-of-Service (DoS) protection.
- Wired Equivalent Privacy
- Encrypts data as it is transmitted between the wireless client and the access point.
- Service Set Identifier
- Identifies the presence of a wireless network to any wireless client within range by broadcasting the network name in clear text.
Topic 4.1 Exercises
You also examined terminology and technology involved with configuring wireless access points.
Lesson 5. Troubleshooting Networks
After completing this lesson, you should be able to:
- Identify tools, diagnostic procedures, and techniques for troubleshooting networks
Wireless Connection Speed and Strength
If you are not able to connect to the Internet or network resources on a wireless network, you should verify wireless connection speed and strength. You can check these items from the Wireless NIC Properties dialog box. You can also double-click the Wireless Link icon
on the right of the taskbar on a Windows XP computer to perform the same function. To configure a NIC on a Windows XP computer, attach the NIC to any available PCI slot on the motherboard and install the appropriate network card drivers using the Device Manager.
You should connect the NIC to a hub or a switch by using a patch cable. A patch cable is a UTP cable used to connect two devices on a network. A patch cable can be a crossed cable or a straight cable. If you're connecting similar devices, such as two computers, you should use a crossed patch cable. If you're connecting dissimilar devices, such as a computer and a hub or switch, you should use a straight patch cable.
Use Device Manager to check the status of a NIC. Device Manager is used to install device drivers and verify that a device is functioning properly.
To troubleshoot NIC problems, you should check to see whether the link lights are present on a network card.
To verify that the NIC is working properly on a computer, use a loopback device.
Note: If a user can't access the LAN from a computer configured to obtain IP addresses automatically, you should first verify the IP address of the computer. If you run the IPCONFIG command and observe that the computer is using an IP address in the 169.254.x.x range, the computer is unable to contact the DHCP server. If the problem persists, the DHCP server could be down.
To troubleshoot Internet access problems you should check whether the NIC is configured properly. You should check the DNS, DHCP, and default gateway settings to troubleshoot Internet access problems.
DNS is a distributed addressing system that resolves a domain name into its numeric IP address. DNS allows you to use the Internet without the need to remember long lists of cryptic numbers. Each domain is an independent namespace that corresponds to a particular organization, and DNS servers manage requests for information regarding the IP addresses of particular DNS domains.
To configure DNS on a client computer, specify the DNS address provided by your ISP. The procedure involves the following steps:
| Step | Action |
|---|---|
| 1 | Open TCP/IP Properties from the Local Area Connection Properties dialog box. |
| 2 | In the General tab of the TCP/IP Properties dialog box, enter the DNS server's IP address in the Preferred DNS Server field. |
Note: If you are able to PING to a public IP address but are not able to PING the same IP address by using a Fully Qualified Domain Name (FQDN), you should verify the DNS IP settings.
DHCP is a protocol that dynamically delivers IP address configuration information from a central server. DHCP automatically assigns the IP address, subnet mask, and DNS server address to the client computers. A DHCP client performs the following tasks to configure TCP/IP addresses:
| Step | Action |
|---|---|
| 1 | The client starts and enables TCP/IP. |
| 2 | The client discovers that configuration of TCP/IP is set to automatic. The TCP/IP stack sends a DHCPDISCOVER packet to request configuration parameters from a DHCP server. |
| 3 | Each DHCP server on the network responds with a DHCPOFFER packet, which contains an IP address the client can use. |
| 4 | The client accepts the first DHCPOFFER packet it receives and configures itself with that IP address. |
| 5 | The client sends a DHCPREQUEST packet to the DHCP server to accept the IP address. Clients that decline DHCPOFFER packets send DHCPDECLINE packets to the appropriate servers. |
| 6 | The DHCP server responds with a positive acknowledgement, known as a DHCPACK packet, if the IP address is unique on the network. If the DHCP server discovers an IP address conflict, it responds with a negative acknowledgement, known as a DHCPNACK packet. The DHCPNACK packet revokes the IP address and forces the client to send a new request for an IP address. |
| 7 | The client can use the IP address for a limited time, known as the address lease period. When half of the lease time expires, the client will request another address. |
There are a number of things you can do to increase the performance of a network. Upgrade slow networks by using faster devices to connect to the network is one of them.
Let's look at some of these devices.
In the past, bridges were used to connect two different network segments in a LAN and increase the performance of a network. Bridges operated at the data link layer of the Open System Interconnect (OSI) model. But bridges have become obsolete and are not used today.
Switches have replaced hubs, because switches provide faster transmission speeds. If you are using hubs your network performance might be slower than it could be, and it's better to use switches. Switches operate at the data link layer of the OSI model.
A router is a networking device used to forward IP packets to a host on a different network. The process is known as routing. Routers operate at the network layer of the OSI model.
A MAC address is the 48-bit physical address of a NIC. This is a unique address assigned to the NIC by the vendor. To determine the MAC address of a computer, you can use the IPCONFIG /ALL command from the command prompt.
You can check the status of network devices such as NICs or switches by looking at their status indicator lights. A NIC has two indicators: a link indicator and an activity indicator. If the NIC is not properly connected to the network, the link indicator or activity indicator may be off. If the NIC is properly connected to the network, the link status will be green. A blinking activity indicator shows that data is being sent and received over the network. An illuminated indicator light on a NIC card shows that the network cable is connected properly to another Ethernet connection.
Troubleshooting a NIC
The important concepts are:
- LAN tester tool
- Checks that a patch cable is working
- Device Manager
- Helps install device drivers and verify that a device is functioning properly
- Loopback device
- Verifies that a NIC is working properly on a computer
- Link indicator
- Confirms that a NIC is properly connected to a network
- Activity indicator
- Shows that data is being sent and received over a network
In this lesson, you have learned techniques to troubleshoot network problems. You examined connection speed and strength, problems in the NIC, and access problems as being potential trouble spots in a network.
