# cueFlash

## Glossary of CCNA Flash Cards & Exam Practice Pack 2nd Ed

### Deck Info

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What PC component is considered the "brains" of the computer?

CBIF
The CPU is considered the "brains" of the computer. It is the PC component where most calculations take place.
What is the PC bus?

CBIF
The PC bus is a collection of wires through which data is transmitted from one computer component to another. The bus connects all the PC's internal components to the CPU and RAM. Think of the bus as "highways" on which data moves from one component to another.
What is the main function of a PC motherboard?

CBIF
The motherboard provides a bus and data path that connect all components to it. Everything plugs into the motherboard and depends on it to communicate with other devices. It is the nerve center of the computer system.
What is the main function of a Network Interface Card (NIC)?

CBIF
The main function of a NIC is to connect a computer to a network. A computer NIC plugs into the motherboard and connects to the network through a network cable.
How many bits (b) are in a byte (B)?
How many bytes (B) are in a kilobyte (KB)?
How many bits (b) are in a megabyte (MB)?
How many bits (b) are in a nibble?

CBIF
There are 8 bits in one byte. Most computer coding schemes use 8 bits to represent each number, letter, or symbol; 1 byte represents a single addressable storage location.
There are 1000 bytes in a kilobyte and 8 million bits in a megabyte.
There are 4 bits in a nibble.
Convert the decimal number 167 to binary.

CBIF
Convert the decimal number 167 to binary.
Convert the binary number 01100100 to decimal.

CBIF
Converting a binary number to decimal is the reverse of converting a decimal number to binary. When converting from binary, look at the numbers that are considered on, and then find their place value. In the binary number 01100100, the place values 64, 32, and 4 are on. If you add together these place values, you get the decimal number 100.
Convert the binary number 0101011011000010 to hexadecimal.

CBIF
Converting binary to hexadecimal is easier than it looks. No matter how large the binary number, always apply the following conversion: Break the binary number into groups of four, starting on the right and moving left. If the binary number is not divisible by 4, add 0s to the leftmost group end until there are four digits in every group. Using this conversion, 0101011011000010 is broken into the following groups: 0101 0110 1100 0010. After you have the groups, you can convert the digits to hex. 0101 is 5 in hex, 0110 is 6, 1100 is C (the 2 bits that are on are 8 and 4; adding them together produces 12, which is C in hex), and 0010 is 2. Therefore, 0101011011000010 is 0x56C2 in hex.
What are the three layers of the Cisco hierarchical model?

CBIF
The three layers of the Cisco hierarchical model are:
- The access layer
- The distribution layer
- The core layer
In the Cisco hierarchical model, what is the function of the access layer?

CBIF
Sometimes referred to as the desktop layer, the access layer is the point at which users connect to the network. Some functions of the access layer include:
- Connectivity into the distribution layer
- Shared bandwidth
- Segmentation
- Provides a point at which users connect to the network
- Security by allowing access lists to further optimize user needs
What is the function of the distribution layer in the Cisco hierarchical model?

CBIF
Also known as the workgroup layer, the distribution layer is the demarcation point between the network's access and core layers. Its primary function is to provide boundary definition, and it's where packet manipulation takes place. Routing, route summarization, filtering, and WAN access also occur at the distribution layer. The distribution layer determines how packets access the core, so it is the layer at which policy-based connectivity is implemented. Some of the distribution layer's functions are as follows:
- Collection point for access layer devices
- Broadcast and multicast domain segmentation
- Security and filtering services such as firewalls and access lists
- Provides translation between different media types
- Inter-VLAN routing
What is the role of the core layer in the Cisco hierarchical model?

CBIF
The core layer is the backbone of the network. Its main function is to switch traffic as fast as possible. The core layer ensures that every device in the network has full reachability to all other devices. Because its function is to switch traffic as fast as possible, it should not perform any filtering to slow down traffic
What are key reasons why the OSI reference model was created?

CBIF JTB
The OSI reference model was created for the following reasons:
- To create standards that enable vendor interoperability by defining functional guidelines for communication between networked applications
- To clarify general internetworking functions
- To divide the complexity of networking into smaller, more manageable sublayers
- To simplify troubleshooting
- To let developers modify or improve components at one layer without having to rewrite an entire protocol stack
The ISO's OSI reference model contains seven layers. What are they? Include the layer number and the name of each layer in your answer.

CBIF JTB Final
The seven layers of the OSI model are as follows:
Layer 7: Application layer
Layer 6: Presentation layer
Layer 5: Session layer
Layer 4: Transport layer
Layer 3: Network layer
Layer 1: Physical layer
What does the application layer (Layer 7) of the OSI model do? Give some examples of this layer.

CBIF
The application layer is the layer closest to the user. This means that it interacts directly with the software application. The application layer's main function is to identify and establish communication partners, determine resource availability, and synchronize communication. Some examples include the following:
- TCP/IP applications such as Telnet, FTP, Simple Mail Transfer Protocol (SMTP), and HTTP
- OSI applications such as Virtual Terminal Protocol; File Transfer, Access, and Management (FTAM); and Common Management Information Protocol (CMIP)
In the OSI model, what are the responsibilities of the presentation layer (Layer 6)? Give some examples of this layer.

2 functions and 4 examples.

CBIF JTB, Tough
Also known as the translator, the presentation layer provides coding and conversion functions to application layer data. This guarantees that the application layer on another system can read data transferred from the application layer of a different system. Some examples of the presentation layer are:
- Compression and decompression
- Encryption
- JPEG, TIFF, GIF, PICT, QuickTime, MPEG
- EBCDIC and ASCII
What are the functions of the session layer (Layer 5)?
Give some examples.

CBIF JTB
The session layer is responsible for creating, managing, and ending communication sessions between presentation layer entities. These sessions consist of service requests and responses that develop between applications located on different network devices. Some examples include SQL, RPC, X Window System, ZIP, NetBIOS names, and AppleTalk ASP.
What is the transport layer (Layer 4) responsible for?
Give some examples of transport layer implementations.

Does 2 things, provides 7 things.

CBIF JTB Final
The transport layer segments and reassembles data from upper-layer applications into data streams. It provides reliable data transmission to upper layers. End-to-end communications, flow control, multiplexing, error detection and correction, and virtual circuit management are typical transport layer functions. Some examples include TCP, UDP, and SPX.
What is flow control, and what are the three methods of implementing it?

3 methods

CBIF Tough
Flow control is the method of controlling the rate at which a computer sends data with the intention of preventing network congestion. The three methods of implementing flow control are:
- Buffering
- Source-quench messages (congestion avoidance)
- Windowing
Describe the function of the network layer (Layer 3), and give some examples of network layer implementations.

Provides 2 things, defines 1 thing, supports 2 protocols

CBIF JTB Final
The network layer provides internetwork routing and logical network addresses. It defines how to transport traffic between devices that are not locally attached. The network layer also supports connection-oriented and connectionless services from higher-layer protocols. Routers operate at the network layer. IP, IPX, AppleTalk, and DDP are examples of network layer implementations.
Are network layer addresses physical or logical?

CBIF JTB
Network layer addresses are logical addresses specific to the network layer protocol being run on the network. Each network layer protocol has a different addressing scheme. They are usually hierarchical. They define networks first and then hosts or devices on that network. An example of a network address is an IP address, which is a 32-bit address often expressed in decimal format. 192.168.0.1 is an example of an IP address in decimal format.
What is the responsibility of the data link layer (Layer 2)?

CBIF
The IEEE defines what two sublayers of the data link layer?

CBIF JTB
The two sublayers of the data link layer are:
- The Logical Link Control (LLC) sublayer
- The MAC sublayer
These two sublayers provide physical media independence.
For what is the LLC sublayer responsible?

2 responsibilities + 2 PDU types

CBIF JTB Tough
The Logical Link Control (802.2) sublayer is responsible for identifying different network layer protocols and then encapsulating them to be transferred across the network. There are two types of LLC frames: service access point (SAP) and Subnetwork Access Protocol (SNAP). An LLC header conveys to the data link layer what to do with a packet after it is received.
What functions does the MAC sublayer provide?

Specifies 2 things, controls 1 thing, defines 4 things

CBIF JTB Tough
The MAC sublayer specifies how data is placed and transported over the physical wire. It controls access to the physical medium. The LLC layer communicates with the network layer, but the MAC layer communicates downward directly with the physical layer. Physical addressing (MAC addresses), network topologies, error notification, and delivery of frames are defined at this sublayer.
What are some network devices that operate at the data link layer?

CBIF
Bridges and switches are network devices that operate at the data link layer. Both devices decide what traffic to forward or drop (filter) based on MAC addresses. Logical network addresses are not used at this layer. Data link layer devices assume a flat address space.
What is the function of the OSI model's physical layer (Layer 1)? Give some examples of physical layer implementations.

Defines 4 things. Includes 3 things

CBIF JTB Final
The physical layer defines the physical medium. It defines the media type, the connector type, and the signaling type (baseband versus broadband). This includes voltage levels, physical data rates, and cable specifications. The physical layer is responsible for converting frames into electronic bits of data, which are then sent or received across the physical medium. Twisted pair, coaxial cable, and fiber-optic cable operate at this level. Repeaters and hubs are network devices that operate at the physical layer.
How do the different layers of the OSI model communicate with each other?

CBIF JTB
Each layer of the OSI model can communicate only with the layer above it, below it, and parallel to it (a peer layer). For example, the presentation layer can communicate with only the application layer, session layer, and presentation layer on the machine it is communicating with. These layers communicate with each other using SAPs and protocol data units (PDUs). The SAP is a conceptual location at which one OSI layer can request the services of another OSI layer. PDUs control information that is added to the user data at each layer of the model. This information resides in fields called headers (the front of the data field) and trailers (the end of the data field).
What is data encapsulation?

CBIF JTB Final
A PDU can include different information as it goes up or down the OSI model. It is given a different name according to the information it is carrying (the layer it is at). When the transport layer receives upper-layer data, it adds a TCP header to the data; this is called a segment. The segment is then passed to the network layer, and an IP header is added; thus, the data becomes a packet. The packet is passed to the data link layer, thus becoming a frame. This frame is then converted into bits and is passed across the network medium. This is data encapsulation. For the CCNA test, you should know the following:
- Application layer: Data
- Transport layer: Segment
- Network layer: Packet
- Physical layer: Bits
What are two types of Layer 1 network devices?
Two types of Layer 1 network devices are:
- Repeaters: Repeaters regenerate and retime network signals, amplifying them, which allows the signal to travel a longer distance on a network medium.
- Hubs: A hub is also known as a multiple-port repeater. It also regenerates and retimes network signals. The main difference between a hub and a repeater is the number of cables that connect to the device. A repeater typically has two ports, whereas a hub has from four to 48 ports.
What are some network devices that operate at the data link layer (Layer 2)?
Bridges and switches are network devices that operate at the data link layer. Both devices decide what traffic to forward or drop (filter) based on MAC addresses. Logical network addresses are not used at this layer. Data link layer devices assume a flat address space.
Typically, a bridge is designed to create two or more LAN segments and is usually implemented in software.
A switch is a high-speed multiport bridge that is typically implemented in hardware. Switches are designed to replace hubs while providing the filtering benefits of bridges.
What are collision domains?
A collision domain defines a group of devices connected to the same physical medium.
A collision occurs when two packets are sent at the same time and collide with each other (electronically). When a collision occurs, a jam signal is sent by the workstation detecting the collision to clear the segment. A jam signal affects all the machines on the segment, not just the two that collided; when the jam signal is on the wire, no workstations can transmit data. The more collisions that occur in a network, the slower it is, because the devices have to resend the packet.
What devices are used to break up collision domains?
Switches, bridges, and routers are used to break up collision domains. They create more collision domains and fewer collisions. Each port on a bridge, switch, and router creates one collision domain. For example, a switch with 24 ports has 24 separate collision domains.
At what layer of the OSI model do routers and multilayer switches function?
Routers and some multilayer switches function at the network layer (Layer 3) of the OSI model. Both devices learn, record, and maintain awareness of different networks. They decide the best path to these networks and maintain the following information in a routing table:
- Protocol-specific network addresses. If you run more than one protocol, each one has a network address.
- The interface the router uses to route a packet to a different network.
- A metric, which is the distance to a remote network or the weight of the bandwidth, load, delay, and path's reliability to the remote network.
In addition to learning the remote network and providing a path to the network, what other functions do routers carry out?
- By default, they do not forward broadcasts or multicasts.
- Routers can perform bridging, encapsulation, and routing functions.
- If a router has multiple paths to a destination, it can determine the best path to the destination.
- Routers forward traffic based on Layer 3 destination addresses.
- Routers can connect virtual LANs (VLANs) by routing traffic between them.
- Routers can provide quality of service for specified types of network traffic.
- Routers provide security, packet filtering, and address translation.
A broadcast domain defines a group of devices that receive each others' broadcast messages. As with collisions, the more broadcasts that occur on the network, the slower the network will be. This is because every device that receives a broadcast must process it to see if the broadcast is intended for it.
What devices are used to break up broadcast domains?
Routers are used to break up broadcast domains. They create more broadcast domains and smaller broadcast areas.
Describe the difference between a physical network topology and a logical network topology.
All of today's networks have physical and logical topologies. Physical topologies refer to the physical layout of devices and network media. Logical topologies refer to the logical paths in which data accesses the medium and transmits packets across it.
What are the five types of physical topologies implemented in today's networks?
The five most common physical network topologies implemented today are:
- Bus
- Ring
- Star
- Extended star
- Mesh
What physical network topology connects all devices to one cable?
A bus topology connects all devices to a single cable. This cable connects from one computer to another. In a logical bus topology, only one packet can be transmitted at a time.
Describe a star and extended star physical topology.
A star or extended star physical topology is made up of a central connection point, such as a hub or switch, where all cable segments connect. A star topology resembles spokes in a wheel. It is the network topology of choice in Ethernet networks.
When a star network is expanded to include additional network devices that connect to a main center network device, it is called an extended star topology.
Describe a ring topology.
In a ring topology, all hosts and devices are connected in a ring or circle. There are two types of ring networks:
- Single-ring: In a single-ring network, all devices share a single cable, and data travels in one direction. Each device waits its turn to send data over the network.
- Dual-ring: A dual-ring network has a second ring to add redundancy and allows data to be sent in both directions.
What physical network topology connects all devices to each other?
A mesh network connects all devices to each other for fault tolerance and redundancy.
What are LANs?
LANs are high-speed, low-error data networks that cover a small geographic area. LANs are usually located in a building or campus and do not cover a large distance. They are relatively inexpensive to develop and maintain. LANs connect computers, printers, terminals, and other devices in a single building or a limited area.
What are LAN standards?
LAN standards define the physical medium and connectors used to connect to the medium at the physical layer. They also define how devices communicate at the data link layer. LAN standards encompass Layers 1 and 2 of the OSI model. Examples of LAN standards are Ethernet and IEEE 802.3.
What do the Ethernet and IEEE 802.3 standards define?
The Ethernet and IEEE 802.3 standards define a bus topology LAN that operates at a baseband signaling rate of 10 Mbps, referred to as 10BASE. Within the Ethernet standards are protocol specifications that define the transmission medium and access. There are three protocol specifications:
- 10BASE2[md]Known as thin Ethernet. Uses thin coaxial cable as its medium. Provides access for multiple stations on the same segment.
- 10BASE5[md]Called thick Ethernet. Uses a thick coaxial cable as its medium. The maximum segment length of 10BASE5 is more than twice that of 10BASE2.
- 10BASE-T[md]Provides access for a single station only, so all stations connect to a switch or hub. The physical topology of 10BASE-T is that of a star network. It uses unshielded twisted-pair (UTP) Category 3, 4, 5, and 5e as its network medium.
Define the Fast Ethernet standard.
The Ethernet standard that defines Fast Ethernet is IEEE 802.3u. This standard raises the speed of the Ethernet standard of 10 Mbps to 100 Mbps with only minimal changes to the existing cable structure. The Fast Ethernet standard defines different protocol specifications depending on the physical medium used. The following are the four different Fast Ethernet specifications:
- 100BASE-FX[md]Uses two strands of multimode fiber-optic cable as its medium. Its maximum segment length is 400 meters.
- 100BASE-T[md]Defines UTP as its medium. Its maximum segment length is 100 meters.
- 100BASE-T4[md]Uses four pairs of Category 3 to 5 UTP as its medium. Its maximum segment length is 100 meters.
- 100BASE-TX[md]Specifies two pairs of UTP or shielded twisted-pair (STP) as its medium. It has a maximum segment distance of 100 meters.
What does BASE mean in 10BASE-T and 100BASE-T?
BASE in 10BASE-T and 100BASE-T refers to the baseband signaling method. Baseband is a network technology in which only one carrier frequency is used. This means that when a device transmits, it uses the entire bandwidth on the wire and doesn't share it. Ethernet defined baseband technology.
What is Gigabit Ethernet?
Gigabit Ethernet is an extension of the IEEE 802.3 Ethernet standard. It increases the speed of the Ethernet protocol to 1000 Mbps or 1 Gbps. IEEE 802.3z specifies Gigabit over fiber, and IEEE 802.3ab specifies Gigabit over twisted-pair cable.
What is carrier sense multiple access collision detect (CSMA/CD)?
CSMA/CD describes the Ethernet access method. In CSMA/CD, many stations can transmit on the same cable, and no station has priority over any other. Before a station transmits, it listens on the wire (carrier sense) to make sure that no other station is transmitting. If no other station is transmitting, the station transmits across the wire. If a collision occurs, the transmitting stations detect the collision and run a backoff algorithm. The backoff algorithm is a random amount of time that each station waits before retransmitting.
WANs operate at what three layers of the OSI model?
WANs operate at the physical, data link, and network layers of the OSI model.
A WAN interconnects LANs that are separated by a large geographic distance that is not supported by typical LAN media.
What are the four available WAN connection types?
The four available WAN connection types are:
- Dedicated connections (leased lines)
- Circuit-switched connections
- Packet-switched connections
- Cell-switched connections
List four devices used to connect to a WAN or used on a WAN.
Four devices used to connect to a WAN or used on a WAN are:
- Routers[md]Connect the LAN to the WAN. Routers provide network layer services and route data from one network to another.
- WAN switches[md]Used in the WAN network, switches are multiport devices that switch Frame Relay, X.25, and ATM traffic. They operate at the data link layer of the OSI model.
- Modems[md]Interpret analog and digital signals. Modems modulate and demodulate a signal, allowing data to be transmitted over telephone lines.
- CSUs/DSUs[md]Convert from one digital format to another. CSUs/DSUs are a digital interface (sometimes two separate interfaces) that connects the physical interface of a data terminal equipment (DTE) device to the interface of a data communications equipment (DCE) device. An example of a DTE device is a terminal, and an example of a DCE device is a switch. Most routers today offer an integrated CSU/DSU interface.
Define customer premises equipment (CPE), and give an example.
CPE is equipment that is located on the customer's (or subscriber's) premises. It is equipment owned by the customer or equipment leased by the service provider to the customer. An example is your router.
What is the demarcation point (demarc)?
The demarc is a point where the CPE ends and the local loop begins. It is the point between the wiring that comes in from the local service provider (telephone company) and the wiring installed to connect the customer's CPE to the service provider. It is the last responsibility of the service provider and is usually a network interface device (NID) located in the customer's telephone wiring closet. Think of the demarc as the boundary between the customer's wiring and the service provider's wiring.
What is the local loop?
The local loop is the physical cable that extends from the demarc to the central office.
What is the central office (CO)?
The CO is the WAN service provider's office where the local loop terminates and where circuit switching occurs.
What is WAN signaling?
WAN signaling is the process of sending a transmission signal over a physical medium for communication. WAN transmission facilities feature standardized signaling schemes that define transmission rates and media types. For example, the signaling standard for a T1 line in North America is DS1 with a transmission rate of 1.544 Mbps.
What are WAN data link layer protocols?
Designed to operate over dedicated lines, multipoint, and multiaccess switched services such as Frame Relay, data link layer protocols provide the data link layer encapsulations associated with synchronous serial lines. Examples include HDLC, PPP, SLIP, LAPD, and LAPF.
Describe Wireless signals.
Wireless signals are electromagnetic waves that travel through air or space. They do not require a network medium such as copper or fiber, but use air as its medium. Because wireless signals are not bound by physical cable, they are very versatile and can be implemented in a variety of ways.
The part of the electromagnetic spectrum that transmits voice, video, and data is referred to as the radio spectrum.
What is the frequency range the radio spectrum uses?
The radio spectrum uses frequencies from 3 kilohertz (kHz) to 300 gigahertz (GHz).
What are the most common types of wireless data communication used today?
The most common types of wireless data communication used today are:
- Infrared (IR) - provides very high data rates at a low cost, but at a very short distance. Must be line of sight.
- Narrowband - provides low data rates at a medium cost. A license is required and covers a limited distance.
- Spread spectrum - has a medium cost but very high data rates. It is limited to campus coverage. Cisco Aironet products are an example of spread spectrum wireless devices.
- Broadband personal communications service (PCS) - mainly used for cellular networks, PCS provides low data rates and broad coverage.
- Circuit and packet data (cellular and cellular digital packet data [CDPD]) provides low data rates, high packet fees, and national coverage.
- Satellite - provides worldwide coverage and has low data rates at a high cost.
What is modulation?
Modulation is the process by which amplitude, frequency, or phase of an RF or light wave is change to transmit data. The most common methods of modulation are:
- Amplitude modulation (AM)
- Frequency modulation (FM)
What is the wireless standard used in most of today’s wireless LANs?
802.11b is the most common wireless standard used in today’s LANs. 802.11a is new and upcoming wireless standard that improves upon 802.11b.
Name two security protocols used in today’s 802.11b networks.
Two security protocols used in today’s 802.11b networks are:
- WEP - 40-bit or 128-bit encryption over an 802.11b network. Uses the RC4 stream cipher for encryption. Can be hacked into very easily.
- 802.1/EAP - provides centralized authentication and dynamic key distribution for encryption. EAP allows wireless clients that support different authentication types to communicate with different back-end servers.
Describe twisted-pair cable.
Twisted-pair cable is a transmission medium that consists of pairs of cables twisted together to provide protection against crosstalk. When electrical current flows through a wire, it creates a small, circular magnetic field around the wire. When two wires are placed close together, their magnetic fields cancel each other out and cancel out other magnetic interference.
Twisted-pair cable is the cabling used in telephone communications and in most Ethernet networks. Two types of twisted-pair cable exist: unshielded twisted-pair (UTP) and shielded twisted pair (STP).
What is UTP cable?
UTP cable is a type of twisted-pair cable that relies solely on the cancellation effects produced by the twisted wire pairs to limit electromagnetic interference (EMI) and radio frequency interference (RFI). UTP cable is often installed using an RJ-45 connector. UTP cabling must follow precise specifications dictating how many twists are required per meter of cable. Advantages of UTP are ease of installation and cost. A disadvantage of UTP is that it is more prone to EMI than other media.
What are the differences between STP and UTP cable?
STP cable combines the twisting techniques of UTP, but each pair of wires is wrapped in a metallic foil. The four pairs of wires then are wrapped in a metallic braid or foil. STP reduces electrical noise and EMI. STP is installed with an STP data connector but can also use an RJ-45 connector. An advantage of STP is that it prevents outside interference. Two disadvantages are that it is more expensive than UTP and is difficult to install.
What is the maximum cable length for STP?
The maximum cable length for STP is 100 meters or 328 feet.
What type of network medium is used in thinnet?
Thinnet and thicknet use coaxial cable as their network medium. The difference between the two is the thickness of the coaxial cable used. Coaxial cable can be cabled over a longer distance than UTP, but it is more costly than UTP.
What are the two types of fiber-optic cable? Describe the characteristics of each type.
The two types of fiber-optic cable are:
- Single-mode
- Multimode
Single-mode fiber allows only one mode (or wavelength) of light through the fiber. It is capable of greater distances and higher bandwidth than multimode fiber and often is used for campus backbones. Single-mode fiber uses lasers as the light-generating method. Its maximum cable length is more than 10 km.
Just as the name implies, multimode fiber allows multiple modes of light to propagate through the fiber. It uses LEDs as a light-generating device. Its maximum cable length is 2 km.
What is a straight-through Ethernet cable, and when would you use it?
A straight-through Ethernet cable is the same at both ends. A straight-through cable uses pins 1, 2, 3, and 6. The send and receive wires are not crossed. You should use a straight-through Ethernet cable when connecting dissimilar devices (a DTE to a DCE). Examples include connecting PCs (DTE) to switches or hubs (DCE) or connecting a router (DTE) to a switch or hub (DCE).
What is a crossover Ethernet cable, and when would you use it?
A crossover Ethernet cable has the send and receive wires crossed at one of the ends. On a Category 5 cable, the 1 and 3 wires are switched, and the 2 and 6 wires are switched on one of the cable's ends. You should use a crossover cable when connecting similar devices (DCE to DCE), such as when you connect a router to a router, a switch to a switch or hub, a hub to a hub, or a PC to a PC.
What is the maximum cable length for each of the following?
- 10BASE2
- 10BASE5
- 10BASE-T
- 10BASE-FL
- 100BASE-T
The maximum cable lengths are as follows:
- 10BASE2 (thinnet)[md]185 meters
- 10BASE5 (thicknet)[md]500 meters
- 10BASE-T[md]100 meters
- 10BASE-FL[md]On multimode fiber:
-- 400 m (1312 ft) for any repeater-to-DTE fiber segment
-- 500 m (1640 ft) with four repeaters and five segments
-- 1000 m (3280 ft) for any interrepeater fiber segment
-- 2km (6561 ft) without a repeater
-100BASE-T[md]100 meters
What is the difference between baseband and broadband?
Baseband is a network technology in which only one carrier frequency is used (such as Ethernet). Broadband is a network technology in which several independent channels are multiplexed into one cable (for example, a T1 line).
What is serial transmission?
Serial transmission is a method of data transmission in which bits of data are transmitted sequentially over a single channel. WANs use serial transmission.
In WAN communications, what is clocking?
Clocking is the method used to synchronize data transmission between devices on a WAN. The CSU/DSU (DCE device) controls the clocking of the transmitted data.
How many channels (timeslots) are in a full point-to-point or Frame Relay T1 line?
A T1 line has 24 channels or timeslots. Each channel is 64 Kb.
This information is useful, because not all companies buy a full T1 line. ISPs offer fractional T1 lines that are half the cost of a T1; this might be an option for branch offices that do not require a full T1. When configuring a router for a fractional T1, you need to configure the proper timeslots on the CSU/DSU. If the CSU/DSU is internal to the router (a WIC), you configure the timeslots in the router's serial interface. If the CSU/DSU is external, you configure the external device. The default configuration on a Cisco interface is a full T1 (all 24 channels).
How do you set up a console session to a Cisco device?
To set up a console session to a Cisco device, you connect a rollover cable to the console port on the Cisco device. You then connect the other end to a DB-9 adaptor and connect the DB-9 adaptor to the serial port on your PC. You then configure a terminal emulation application to the following com settings: 9600 bps, 8 data bits, no parity, 1 stop bit, and no flow control.
What are the three ways in which LAN traffic is transmitted?
LAN traffic is transmitted in these three ways:
- Unicast: The most common type of LAN traffic. A unicast frame is intended for only one host.
- Multicast: Traffic in which one transmitter tries to reach only a subset, or group, of the entire segment.
What happens when you segment the network with hubs/repeaters?
Because hubs and repeaters operate at the physical layer of the OSI model, segmenting a network with these devices appears as an extension to the physical cable. Hubs and repeaters are transparent to devices. They are unintelligent devices. All devices that connect to a hub/repeater share the same bandwidth. Hubs/repeaters create a single broadcast and collision domain.
What is the advantage of segmenting a network with bridges/switches?
Bridges/switches operate at Layer 2 of the OSI model and filter by MAC address. Each port on a bridge/switch provides full dedicated bandwidth and creates a single collision domain. Because bridges/switches operate at Layer 2 of the OSI model, they cannot filter broadcasts, and they create a single broadcast domain.
List four advantages that Layer 2 switches have over bridges.
Four advantages that Layer 2 switches have over bridges are:
- A high-speed backplane that lets multiple simultaneous conversations occur
- Data-buffering capabilities are used to store and forward packets to the correct ports or port.
- Higher port densities versus bridges
- Lower latency than bridges. Layer 2 switches are implemented in hardware, allowing millions of bits per second to be transmitted at the same time.
Broadcast storms occur when many broadcasts are sent simultaneously across all network segments. They are usually caused by a bad NIC, faulty network device, or virus. All devices on a network process broadcast packets, so an excess of broadcasts on a network causes all devices to slow down.
A fundamental concept behind LAN switching is that it provides microsegmentation. What is microsegmentation?
Microsegmentation is a network design (functionality) in which each workstation or device on a network gets its own dedicated segment (collision domain) to the switch. Each network device gets the segment's full bandwidth and does not have to share the segment with other devices. Microsegmentation reduces collisions, because each segment is its own collision domain.
What three major functions do Layer 2 switches provide?
The three major functions that Layer 2 switches provide are:
- Packet forwarding/filtering
- Loop avoidance by spanning tree
Describe full-duplex transmission.
Full-duplex transmission is achieved by microsegmentation, in which each network device has its own dedicated segment to the switch. Because the network device has its own dedicated segment, it does not have to worry about sharing the segment with other devices. With full-duplex transmission, the device can send and receive at the same time, effectively doubling the amount of bandwidth between nodes.
What are the three switching methods (frame transmission modes) in Cisco Catalyst switches?
The three frame operating modes that handle frame switching are:
- Store-and-forward
- Cut-through
- Fragment-free
What is the Cisco Catalyst store-and-forward switching method?
In the store-and-forward switching method, the switch's incoming interface receives the entire frame before forwarding it. The switch computes the cyclic redundancy check (CRC) to make sure that the frame is not bad. If the frame is good, the switch forwards it. If the CRC is bad, the switch drops it. If the frame is a runt (less than 64 bytes, including the CRC) or a giant (more than 1518 bytes, including the CRC), the switch discards it. Because the switch stores the frame before forwarding it, latency is introduced in the switch. Latency through the switch varies with the frame's size.
What is the Cisco Catalyst cut-through switching method?
In cut-through switching mode, the switch checks only the frame's destination address and immediately begins forwarding the frame out the appropriate port. Because the switch checks the destination address in only the header and not the entire frame, the switch forwards a collision frame or a frame that has a bad CRC. This results in a fixed latency switch. Cut-through can be used only between same-speed interfaces.
What is the Cisco Catalyst fragment-free switching method?
Also known as modified cut-through, fragment-free switching checks the first 64 bytes before forwarding the frame. If the frame is less than 64 bytes, the switch discards it. Ethernet specifications state that collisions should be detected during the first 64 bytes of the frame. By reading the first 64 bytes of the frame, the switch can filter most collisions, although late collisions are still possible.
What is Spanning-Tree Protocol (STP)?
STP is a loop-prevention bridge-to-bridge protocol. Its main purpose is to dynamically maintain a loop-free network. It does this by sending out bridge protocol data units (BPDUs), discovering any loops in the topology, and blocking one or more redundant links.
How does STP maintain a loop-free network?
STP maintains a loop-free network by:
- Electing a root bridge
- Electing a root port on each nonroot bridge
- Electing designated ports on each segment
- Putting in the blocking state any redundant port that is not a root port or designated port
What are the five spanning tree port states?
The five spanning tree port states are:
- Blocking
- Listening
- Learning
- Forwarding
- Disabled
What is a Layer 3 switching device?
A Layer 3 switching device is a switch that has routing (Layer 3) functionality. It is a cross between a router and a switch. Each port on the switch is a separate LAN port, but the forwarding engine can store and forward packets based on Layer 3 information. In basic terms, a Layer 3 switch performs hardware-based routing.
What are Layer 4 switching devices?
Layer 4 switching devices perform hardware-based Layer 3 routing that accounts for Layer 4 control information. A Layer 4 switch can make forwarding decisions based not just on MAC addresses or source/destination IP addresses but on Layer 4 information such as port numbers. With a Layer 4 switch, the network administrator can program the switch to perform quality of service (QoS) or to control network traffic flow.
What are VLANs?
VLANs are broadcast domains in a Layer 2 network. Each broadcast domain is like a distinct virtual bridge within the switch. Each virtual bridge you create in a switch defines a broadcast domain. By default, traffic from one VLAN cannot pass to another VLAN without crossing a Layer 3 boundary such as a router or routed port. Each of the users in a VLAN is also in the same IP subnet. Each switch port can belong to only one VLAN.
For VLANs to communicate with each other, what network component is needed?
A router is needed for inter-VLAN communication. It is important to think of a VLAN as a distinct virtual bridge in a switch that is its own IP subnet and broadcast domain. A network device cannot communicate from one IP subnet to another without a router. The same is true of a VLAN. You cannot communicate from one VLAN to another without a router.
What is VLAN membership?
VLAN membership describes how a port on a switch is assigned to a VLAN.
What are the three most common ways that VLAN membership is established?
The three most common ways of establishing VLAN membership are:
- Port-driven membership
- Layer 3-based membership
The administrator statically determines port-driven membership by manually assigning each port to a particular VLAN.
MAC address and Layer 3-based memberships occur dynamically. MAC address membership is determined by a database that contains all the MAC addresses in the network and the VLAN they belong to. When the switch sees a MAC address, it performs a lookup in the database to determine what VLAN the MAC address belongs to. Layer 3-based membership occurs by looking at the Layer 3 information in the packet to determine what VLAN the packet belongs to. Because the switch has to look at the Layer 3 information, the switch must be a Layer 3 switch, and the lookup is more time-consuming than looking at the MAC address.
What are the two ways in which inter-VLAN communication can be established?
The two ways in which inter-VLAN communication can be established are:
- Logically
- Physically
Logical connectivity involves a single connection, called a trunk link, from the switch to a router. The trunk link uses a VLAN protocol to differentiate between VLANs. This configuration is called a "router on a stick."
Physical connectivity involves a separate physical connection for each VLAN.
By default, each port on a switch can belong to only one VLAN. For devices that are in VLANs (that span multiple switches) to talk to other devices in the same VLAN, you must use trunking or have a dedicated port per VLAN. Trunk links allow the switch to carry multiple VLANs across a single link.
What are the two most common trunking protocols supported by Cisco switches?
The two most common trunking protocols supported by Cisco are:
- IEEE 802.1Q
ISL is a Cisco-proprietary protocol used to interconnect switches that have multiple VLANs. It maintains VLAN information as traffic goes between switches, allowing the traffic to enter the correct VLAN. ISL operates in a point-to-point environment.
Describe 802.1Q tagging.
802.1Q tagging provides a standard method for identifying frames that belong to a particular VLAN. It does this by using an internal process that modifies the existing Ethernet frame with the VLAN identification. Because 802.1Q modifies the existing frame, the identification process can work on both access links and trunk links. This is because the frame appears as a regular Ethernet packet.
What is a protocol?
A protocol is a standard set of rules that determine how network devices communicate with each other. A protocol describes the format that the message must take and how network devices must exchange a message.
What are the four layers of the TCP/IP model?
The four layers of the TCP/IP model are:
- Application (process)
- Host-to-host (transport)
- Internet
- Network interface (physical and data link)
What two protocols function at the transport (host-to-host) layer of the TCP/IP model?
The two protocols that function at the host-to-host layer of the TCP/IP model are TCP (Transmission Control Protocol) and UDP (User Datagram Protocol). TCP is a connection-oriented, reliable protocol. UDP is a connectionless and unacknowledged protocol.
What are the three mechanisms TCP uses to establish and maintain a connection-oriented connection?
The three mechanisms that TCP uses to establish and maintain a connection-oriented connection are:
- Packet sequencing
- Acknowledgments, checksums, and timers
- Windowing
What are the steps for the TCP three-way handshake?
The steps for the TCP three-way handshake are as follows:
1. The source host sends a SYN to the destination host.
2. The destination host replies to the source with an ACK. At the same time, it sends a SYN to the source host.
3. The source host replies with an ACK.

For the CCNA exam, remember this:
Step 1, SYN; Step 2, SYN/ACK; Step 3, ACK.
What are the protocol numbers for TCP and UDP?
The protocol number for TCP is 6. The protocol number for UDP is 17.
What are TCP and UDP port numbers?
To pass information (such as e-mail) to upper layers, TCP and UDP use port numbers. These port numbers are predefined and keep track of different conversations among different hosts at the same time. Originating source port numbers are dynamically assigned by the source host, which is a number greater than 1023.
What is the number range for "well-known" port numbers?
Defined in RFC 1700, the well-known port numbers are 1 to 1023.
What is the main advantage of UDP over TCP?
Although UDP has different advantages over TCP, the main advantage is its low overhead. Because UDP segments are not acknowledged, they do not carry the overhead that TCP does, thus allowing faster transmissions and greater efficiency.
What are some protocols that operate at the TCP/IP Internet layer?
Some protocols that operate at the TCP/IP Internet layer are:
- IP
- ICMP
- ARP
- RARP
What is IP?
IP is a connectionless protocol that provides best-effort delivery of packets.
What is Internet Control Message Protocol (ICMP)?
ICMP is a management protocol for IP. ICMP messages are carried in IP packets and are used to send error and control messages. An example of a utility that uses ICMP is echo and echo reply (ping).
What is Address Resolution Protocol (ARP)?
ARP is used to resolve a known IP address to a MAC address. For a host to communicate with another host, it must know the MAC address of the destination host (if they are on the same network) or the next-hop router. This is the reason for ARP.
What is Reverse Address Resolution Protocol (RARP)?
RARP is a protocol used to find the IP address of a station that knows its MAC address. It is mainly used for diskless workstations that boot up and need an IP address. An RARP request is a broadcast packet. BOOTP is an example of RARP.
True or false: ICMP is implemented by all hosts configured for TCP/IP.
ICMP operates at the Internet layer (OSI network layer) and is used by IP for many different services. ICMP messages are carried as IP packets.
What are BOOTP and DHCP?
BOOTP is a protocol used by a device to obtain an IP address at startup. A client with BOOTP enabled uses UDP to send a broadcast datagram. When the BOOTP server sees the broadcast, it responds to the client's MAC address with the IP address the client should use.
DHCP is a newer version of BOOTP and has replaced it altogether. DHCP allows a host to obtain an IP address quicker than BOOTP. All that is required for using DHCP is a defined range of IP addresses on a DHCP server.
What is a socket?
A socket is an IP address combined with a TCP or UDP port number. When a host wants to talk to another host, it sends its IP address along with the application (port number) it wants to communicate with. For example, if host 192.168.0.3 wants to talk to host 192.168.0.2 by e-mail, host 192.168.0.3 sends its IP address and destination port number (192.168.0.3:1023) to the host 192.168.0.2 with the port number it wants to communicate with (192.168.0.2:25).
What are the different classes of IP addressing and the address ranges of each class?
The address ranges are as follows:
- Class A: 1.0.0.0 to 126.0.0.0
- Loopback: 127.0.0.0 to 127.255.255.255
- Class B: 128.0.0.0 to 191.255.0.0
- Class C: 192.0.0.0 to 223.255.255.0
- Class D: 224.0.0.0 to 239.255.255.255 (multicasting)
- Class E: 240.0.0.0 to 255.255.255.254 (reserved)
What does RFC 1918 define?
RFC 1918 defines reserved (private) networks and addresses that are not routed on the Internet. These addresses are 10.0.0.0 to 10.255.255.255, 172.16.0.0 to 172.31.255.255, and 192.168.0.0 to 192.168.255.255. They are used as internal private addresses. Private addresses are widely used today, along with proxy servers and Network Address Translation (NAT), to help "stretch" the current IP address space.
What is IPv6?
IP version 6 (IPv6) is the new version of IP that is starting to be implemented in today's networks. The current version is IPv4. IPv6 was created to address some of the faults of IPv4, particularly the exhaustion of IPv4 addresses and the size of the Internet routing tables. IPv6 uses 128-bit binary addresses, which allows 3.4 [ts] 1038 IP addresses.
What is CIDR?
Classless Interdomain Routing (CIDR) is a new addressing scheme for the Internet that allows for more-efficient use of IP addresses than the old Class A, B, and C scheme. It is more flexible and offers route aggregation (supernetting). A CIDR address is a network address that does not use original Class A, B, and C rules. For example, a CIDR address can look like this: 192.168.2.0 255.255.255.248.
How many usable subnets and hosts will you have if you subnet the network address 192.168.1.0 with the subnet mask 255.255.255.240?
If you subnet 192.168.1.0 with a 28-bit mask (255.255.255.240), you will have 14 networks with 14 hosts in each network. If you look at the network address and subnet mask in binary, you see that in the last octet you have 4 bits for networks and 4 bits for hosts:
11000000.10101000.00000000.00000000
11111111.11111111.11111111.11110000
Apply these bits to the following formula:
2x [nd] 2 = the number of subnets or hosts
where x is the number of masked bits.
24 [nd] 2 = 14 subnets. You then apply the same equation to find the hosts, and you receive 14.
Your Internet service provider gives you the IP network address 172.16.0.0/16. You have 18 networks, each with 1200 hosts. You want to assign one IP range per network, leaving room for future growth. What subnet mask would best achieve your goals?
255.255.248.0.
If you look at this subnet mask in binary, you see that there are 5 subnet bits for the network address:
11111111.11111111.11111000.00000000
If you use the subnet equation (25 [nd] 2 = 30), 30 available networks are provided with the subnet mask, which fulfils the requirement for 18 networks and allows for adequate growth. This leaves you with 11 bits to be assigned to hosts, giving you 2046 (211 [nd] 2 = 2046) address, giving you more than enough IP addresses to be assigned to hosts. If you use a subnet mask of 255.255.240.0, you will meet the requirement of 1200 hosts (212 [nd] 2 = 4094 available hosts), but you won't have enough networks (24 [nd] 2 = 14 available networks).
What are the TCP port numbers to the following applications?
-HTTP
-FTP
-SMTP
-Telnet
The TCP port numbers are:
-HTTP: 80
-FTP: 20 and 21
-SMTP: 25
-Telnet: 23
Define routing.
Routing is the act of finding a path to a destination and moving information across an internetwork from the source to the destination.
What are the two key functions a router performs?
The two key functions a router performs are routing and switching. The routing mechanism is responsible for learning and maintaining awareness of the network topology. The switching function is the process of moving packets from an inbound interface to an outbound interface.
What is a routing metric?
A routing metric is a factor used to determine a route's desirability. A router uses the metric to determine the best or most optimal path on which network traffic should be forwarded.
What are the 7 most common routing metrics used in routing algorithms?
The most common routing metrics used in routing algorithms are:
a) Bandwidth: A link's data capacity.
b) Delay: The amount of time required to move a packet from source to destination.
c) Load: The amount of activity on the link or network resource.
d) Reliability: A reference to the error rate on each network link.
e) Hop count: The number of routers a packet must take to reach its destination.
f) Ticks: The delay on a data link using IBM PC clock ticks. 1 tick is 1/18 of a second.
g) Cost: A value assigned by the network administrator, usually based on bandwidth or monetary expense on the link.
What is the difference between a routed protocol and a routing protocol? Give examples.
A routed protocol is a protocol suite that provides the information in its network layer to allow a packet to direct traffic. It also defines the use of fields in a packet. Examples of routed protocols are IP, IPX, and DECnet.
A routing protocol is used to find routes in an internetwork, exchange routing tables, and maintain route awareness. Routing protocols determine how routed protocols are routed. RIP, EIGRP, IS-IS, OSPF, and BGP are examples of routing protocols.
What 6 types of information are stored in routing tables?
The types of information stored in routing tables are:
c) Exiting interface
d) Metric
f) Routing protocol used
How do routing protocols maintain their routing tables with each other?
Routing protocols maintain their routing tables through the transmission of routing update messages. Routing update messages are exchanged between routers at periodic intervals or when there is a change in the network topology. The information contained in the routing update messages and how and when updates are sent varies from routing protocol to routing protocol.
What is administrative distance? What is its range? When is it important?
Administrative distance (AD) is an integer from 0 to 255 that rates the trustworthiness of the source of the IP routing information. It is important only when a router learns about a destination route from more than one source. The path with the lower AD is the one given priority.
What is the AD for each of the following?
- Directly connected interface
- Static route
- EBGP
- EIGRP
- IGRP
- OSPF
- IS-IS
- RIP
- External EIGRP
- IBGP
- Unknown
- Directly connected interface 0
- Static route 1
- EBGP: 20
- EIGRP: 90
- IGRP: 100
- OSPF: 110
- IS-IS: 115
- RIP: 120
- External EIGRP: 170
- IBGP: 200
- Unknown: 255
What is an autonomous system (AS)?
An AS is a collection of networks under common administrative control sharing a common routing strategy.
What is the difference between Interior Gateway Protocol (IGP) and Exterior Gateway Protocol (EGP)? Give examples.
IGP routes data within an autonomous system. EGP routes data between autonomous systems. Examples of IGPs are RIP, EIGRP, IS-IS, and OSPF. BGP is an example of an EGP.
How do distance vector routing protocols function?
Also known as Bellman-Ford algorithms, distance vector routing protocols pass complete routing tables to neighboring routers. Neighboring routers then combine the received routing table with their own routing table. Each router receives a routing table from its directly connected neighbor. RIP and IGRP are the two most common distance vector protocols used in today's internetworks.
How do distance vector routing protocols keep track of any changes to the internetwork?
Distance vector routing protocols keep track of an internetwork by periodically broadcasting updates out all active interfaces. This broadcast contains the entire routing table. This method is often called "routing by rumor."
Slow convergence of distance vector routing protocols can cause inconsistent routing tables and routing loops. What are 5 mechanisms that distance vector protocols implement to prevent routing loops and inconsistent routing tables?
Here are some of the ways distance vector routing protocols prevent routing loops and inconsistent routing tables:
a) Maximum hop count (count to infinity)
b) Split horizon
c) Route poisoning
d) Holddowns
e) TTL
Designed to overcome the limitations of distance vector protocols, link-state protocols respond quickly to network changes and send triggered and periodic updates. Link-state protocols create a picture of the internetwork by determining the status of each interface (link) in the internetwork. When the interface goes down, link-state protocols send updates out all the other interfaces, informing other routers of the downed link. OSPF and IS-IS are the most common link-state protocols.
Which of the following is a hybrid routing protocol?
- RIPv2
- IGRP
- DECnet
- EIGRP
EIGRP is the only hybrid routing protocol listed. EIGRP was developed by Cisco and is considered a hybrid routing protocol because it combines the aspects of distance vector and link-state routing protocols.
If a router with RIP enabled has two paths to the same destination, one path being four routers away and the other path ten routers away, which path does the router choose?
The router chooses the path that is four routers away from the destination. RIP bases its metric on the number of hops (routers) to a destination. The route with the smallest number of hops is considered the best path and is the one used.
If a router running RIP has a path to a network that is 16 hops away, what does the router do to any packets destined for that network?
The router drops all packets. RIP has a hop count limit of 15, so any routes with a hop count of 16 and greater are considered unreachable, and the packet is dropped. RIP has this limitation to prevent a packet from looping infinitely.
What version of RIP supports variable-length subnet masks? Which are classful or classless?
RIP version 2 (RIPv2) supports variable-length subnet masks. RIPv1 is considered a classful protocol because it does not include subnet information with the routing update. RIPv2 is considered a classless protocol because it includes the subnet information with the routing update.
What is Interior Gateway Routing Protocol (IGRP)? What is default hop count? What are its default metrics? Which others can it use?
IGRP is a Cisco-proprietary distance vector routing protocol. IGRP has a default hop count of 100 hops, with a maximum hop count of 255. IGRP uses bandwidth and delay as its default metric, but it can also use reliability, load, and MTU.
What four components does EIGRP include that are not included in IGRP?
EIGRP is an improvement over IGRP and is considered a hybrid protocol. The four components of EIGRP that are not included in IGRP are:
a) Dynamic neighbor discovery
b) Reliable transport protocol guarantees delivery of EIGRP updates
c) DUAL finite-state machine ensures a loop-free internetwork
d) Protocol-dependent modules let EIGRP work with IP, IPX, and AppleTalk
Which of the following are link-state protocols?
- IS-IS
- BGP
- VLSM
- RIP
- OSPF
IS-IS and OSPF are link-state protocols. Both protocols support fast convergence and variable-length subnet masks.
What type of protocol is BGP?
BGP is considered an exterior gateway protocol (EGP).
What port number are BGP updates carried on?
BGP uses TCP port 179 to carry all its routing updates.
WANs use a technology called multiplexing. What is it?
Multiplexing is a technology that lets multiple logical signals be transmitted simultaneously across a single physical channel and then combined into a single data channel at the source. This lets the signals appear as one, combining the speeds of all channels.
List at least eight ways you can connect to a WAN.
Here are eight ways you can connect to a WAN:
a) Leased line
b) Frame Relay
c) Dialup
d) ISDN
e) ATM
f) Cable
g) DSL
h) X.25
How many DS0s are bundled to create a T1 line?
24 DS0s are bundled to create a T1 line. One DS0 is 64 kbps, so 24 x 64 kbps = 1.544 Mbps, the speed of a T1 line.
At what layer of the OSI model does multiplexing occur?
Because multiplexing combines signals across a single physical channel, it occurs at the physical layer of the OSI model.
What are the four types of multiplexing? Describe.
The four types of multiplexing are:
a) Time-division multiplexing (TDM)
b) Frequency-division multiplexing (FDM)
c) Wave-division multiplexing (WDM) and dense WDM (DWDM)
d) Statistical-division multiplexing
In TDM, each data channel is allocated bandwidth based on time slots, regardless of whether data is transferred. Thus, bandwidth is wasted when there is no data to transfer.
In FDM, information of each data channel is allocated bandwidth based on the traffic's signal frequency. An example of this is FM radio.
In WDM and DWDM, each data channel is allocated bandwidth based on wavelength (the inverse of frequency).
In statistical multiplexing, bandwidth is dynamically allocated to data channels.
Describe packet-switched WAN connections. Give 2 examples.
Packet-switched connections use virtual circuits (VCs) to provide end-to-end connectivity. Packet-switched connections are similar to leased lines, except that the line is shared by other customers. A packet knows how to reach its destination by programming of switches. Frame Relay and X.25 are examples of a packet-switched connection.
What are circuit-switched WAN connections? Give two examples.
Circuit-switched WAN connections are dedicated for only the duration of the call or the time required to transmit data. The telephone system and ISDN are examples of circuit-switched networks.
What type of WAN link is a leased line?
A leased line is a point-to-point link that provides a single, preestablished WAN communication path from the customer to the remote network.
Is Frame Relay a circuit-switched or packet-switched network?
Frame Relay is a packet-switched network that creates VCs between two DTE devices on a network to enable bidirectional communication. These VCs can be either permanent (PVCs) or dynamically switched (SVCs).
What type of data can an ATM network transfer?
An ATM network can transfer voice, video, and data. ATM uses a cell-switched network. The cells used to transfer voice, video, and data are always a fixed size.
What is the size of an ATM cell?
An ATM cell is a fixed 53 bytes. This includes a 5-byte header and 48 bytes of payload.
What type of data can ISDN transfer? Why was it created?
ISDN can transfer voice, data, text, graphics, music, and video. ISDN was created to allow faster access over the existing telephone system.
What is the data transfer speed for ISDN BRI? What is the total tranfer rate? What are the various channels? What layers does ISDN operate at?
The data transfer rate for ISDN BRI is 128 kbps. The total transfer rate for ISDN BRI is 144 kbps. This consists of two 64-kbps (128-kbps) bearer (B) channels plus one 16-kbps delta (D) channel. The B channels can be used for data transfer and voice transmission. The D channel carries control and signaling information for fast call setup and can carry user data under certain circumstances. It operates at the first three layers of the OSI model.
What is the total rate in Mbps for ISDN PRI in which countries? What are the component channels?
The total rate for ISDN PRI in the U.S. and Japan is 1.544 Mbps. PRI consists of 23 64-kbps B channels and one 64-kbps D channel. In Europe, PRI consists of 30 B channels and one D channel for a total rate of 2.048 Mbps.
What is Point-to-Point Protocol (PPP)? What can it be used for? What layer does it operate on? What protocols does it operate with?
PPP is an industry-standard protocol that provides router-to-router or router-to-host connections over synchronous and asynchronous links. It can be used to connect WAN links to other vendors' equipment. It works with several network-layer protocols, such as IP and IPX. PPP provides authentication (which is optional) through PAP, CHAP, or MS-CHAP.
What protocol does PPP use to establish, configure, and test the data-link connection?
PPP uses Link Control Protocol (LCP) to establish, configure, and test the data-link connection.
What is the default encapsulation type for serial interfaces on a Cisco router? Is it connection-oriented or not? Can ISO HDLC encapsulate multiple network layer protocols across the same link? Can any kind of HDLC do this?
The default encapsulation for a serial interface on a Cisco router is HDLC. HDLC was derived from Synchronous Data Link Control (SDLC). It is an ISO-standard bit-oriented data-link protocol that encapsulates data on synchronous links. HDLC is a connection-oriented protocol that has very little overhead. HDLC lacks a protocol field and therefore cannot encapsulate multiple network layer protocols across the same link. Because of this, each vendor has its own method of identifying the network-layer protocol. Cisco offers a propriety version of HDLC that uses a type field that acts as a protocol field, making it possible for multiple network layer protocols to share the same link.
At what layer of the OSI model do modems operate?
Modems operate at the physical layer of the OSI model. A modem is used for computer communication through a telephone line.
What modem standard is a worldwide standard that provides 2400 bps at 600 baud? Full or half-duplex?
V.22bis was the first worldwide modem standard for full-duplex modems providing data speeds of 2400 bps at 600 baud.
What modem standard provides up to 56 kbps of downstream data transfer and up to 300 kbps of upstream data transfer?
V.90 is the modem standard that provides up to 56 kbps of downstream data transmission and up to 300 kbps of upstream data transmission.
Describe DSL. What medium does it use? What types are available?
DSL is a modem technology that uses existing twisted-pair telephone lines to transfer high-speed data. Many types of DSL are used today; the most common are asymmetric DSL (ADSL) and symmetric DSL (SDSL). ADSL provides a higher downstream speed than upstream. SDSL provides the same speed for both upstream and downstream traffic.
At what layer of the OSI model does DSL operate? What protocols does it use at upper layers?
DSL operates at the physical layer (Layer 1) of the OSI model. DSL relies on upper-layer protocols to encapsulate the data at the CO. It uses ATM, Ethernet, or PPP at the data link layer and IP at the network layer.
What are the five ways to configure a Cisco device?
The five ways to configure a Cisco device are:
a) Console connection
b) Auxiliary connection (through a modem)
c) Telnet connection
d) HTTP connection
e) CiscoWorks 2000
What two EXEC modes are supported in the Cisco IOS?
The two EXEC modes are:
a) User EXEC mode (user mode)
b) Privileged EXEC mode (enable or privileged mode)
In the IOS, what is user EXEC mode? What can you and can you not do with it? What's the prompt?
User EXEC mode is the first mode you enter when you log into the IOS. This mode is limited and is mostly used to view statistics. You cannot change a router's configuration in this mode. By default, the greater-than sign (>) indicates that you are in user mode. This is how the router prompt looks in user mode:
Router>
In the IOS, what is privileged EXEC mode? What can you do in it? How do you enter it? What's the prompt?
In privileged EXEC mode, you can view and change the configuration in a router; you have access to all the routers commands and the powerful debug commands. To enter privileged mode, enter the enable command while in user mode. By default, the pound symbol (#) indicates that you are in privileged mode. This mode is usually protected with a password. Here is an example of how to enter privileged mode. You also see the output of the prompt:
Router>enable
Router#
When you are in privileged EXEC mode, how do you return to user EXEC mode?
You can return to user EXEC mode using the disable IOS command. Here is an example of using the disable command:
Router#disable
Router>
How do you power on a Cisco 1900 or 2950 series switch?
Unlike a Cisco router, a Cisco 1900 or 2950 series switch does not have a switch to turn the power on and off, so the only way to power on a Cisco switch is the plug in the power cord.
What two types of content-sensitive help are available in the Cisco IOS for a switch and a router?
Word help and command syntax help are the two types of content-sensitive help available in the IOS, whether a switch or a router. Word help uses a question mark and identifies commands that start with a character or a sequence of characters. For example, the following router output shows the use of word help for any IOS command that starts with the letters cl:
Router#cl?
clear clock
Command syntax help is when you use a question mark after a command to see how to complete the command:
Router#clock ?
set Set the time and date
What are the two configuration modes in the Cisco 1900 and 2950 series switches' IOS?
The two configuration modes in the Cisco 1900 and 2950 series switches' IOS are global configuration and interface configuration.
Global configuration is used to configure a global setting on the switch, such as an IP address or host name.
Interface configuration is used to configure an interface setting, such as port speed or duplex.
How do you configure an IP address and subnet mask on a Catalyst 1900 switch and a Catalyst 2950 switch?
To configure an IP address on a Catalyst 2950 switch, you enter the VLAN1 logical interface and then assign the IP address using the ip address address mask command:
Cat2950(config)#interface vlan1
Why would you want to assign an IP address to a Layer 2 device, such as a switch?
You would assign an IP address to a Layer 2 device for management and configuration. With an IP address enabled on a Cisco switch, you can Telnet into it and change the configuration. You can also enable SNMP on the device and remotely monitor the switch.
How do you configure a default gateway on Cisco Catalyst 1900 and 2950 switches?
The command to configure a default gateway on Cisco Catalyst 1900 and 2950 switches is the same. To configure the default gateway, use the ip default-gateway ip-address global configuration command. The following example configures the switch to use IP address 192.168.0.1 as its default gateway:
Cat1900(config)#ip default-gateway 192.168.0.1
What Cisco switch IOS command displays the system hardware, software version, names of configuration files, and boot images?
The show version switch IOS command displays the system hardware, software version, and boot images. The following is output of the show version command on a Cisco 2950 switch:

Cat2950#sh version
Cisco Internetwork Operating System Software
IOS (tm) C2950 Software (C2950-I6Q4L2-M), Version 12.1(9)EA1d,
RELEASE SOFTWARE
(fc1)
Copyright (c) 1986-2002 by cisco Systems, Inc.
Compiled Mon 17-Jun-02 18:55 by antonino
Image text-base: 0x80010000, data-base: 0x804E6000
<text omitted>
FCMain-Core uptime is 25 weeks, 1 day, 8 hours, 51 minutes
System returned to ROM by power-on
System image file is "flash:c2950-i6q4l2-mz.121-9.EA1d.bin"

cisco WS-C2950T-24 (RC32300) processor (revision B0) with 20821K
bytes of memory
.
Processor board ID FAB0525P18E
Last reset from system-reset
Running Enhanced Image
24 FastEthernet/IEEE 802.3 interface(s)
2 Gigabit Ethernet/IEEE 802.3 interface(s)
<Text omitted>
On a Catalyst 1900 switch, what command can you use to view the switch's IP address, subnet mask, and default gateway?
The show ip command displays the 1900 series switch's IP address, subnet mask, and default gateway. Here's an example:
Cat1900#show ip
Default Gateway: 192.168.0.1
Management VLAN: 1
Domain name:
Name server 1: 0.0.0.0
Name server 2: 0.0.0.0
HTTP server : Enabled
HTTP port : 80
RIP : Enabled
Cat1900#
What are global commands on a Cisco router?
Global configuration commands are commands that affect the entire router. They can be executed only in global configuration mode.
How do you enter global configuration mode?
To enter global configuration mode, you enter the config terminal command from privileged EXEC mode. Here is an example of this command:
Router#config terminal
Enter configuration commands, one per line. End with CTRL-Z.
Router(config)#
On a Cisco router, name the enhanced editing commands that are used to do the following:
- Move the cursor to the beginning of the line
- Move the cursor to the beginning of the line: Ctrl-A
On a Cisco router, name the enhanced editing commands that are used to do the following:
- Move the cursor to the end of the line
- Move the cursor to the end of the line: Ctrl-E
On a Cisco router, name the enhanced editing commands that are used to do the following:
- Move the cursor forward one character
- Move the cursor forward one character: Ctrl-F
On a Cisco router, name the enhanced editing commands that are used to do the following:
- Move the cursor back one character
- Move the cursor back one character: Ctrl-B
On a Cisco router, name the enhanced editing commands that are used to do the following:
- Move the cursor back one word
- Move the cursor back one word: Esc-B
On a Cisco router, name the enhanced editing commands that are used to do the following:
- Delete all characters from the cursor to the beginning of the command line
- Delete all characters from the cursor to the beginning of the command line: Ctrl-U
On a Cisco router, name the enhanced editing commands that are used to do the following:
- Complete a word
- Complete a word: Tab
On a Cisco router, name the enhanced editing commands that are used to do the following:
- Display a line versus a screen
- Display a line versus a screen: Enter
What Cisco router command would you use to view a list of the most recently used commands?
The show history command by default displays the last ten commands used:
Router#show history
en
show running-config
show history
enable
show version
show time
show history
Router#
You can also press the up arrow key (or Ctrl-P) to display the last command you entered and the down arrow key (or Ctrl-N) to display the previous commands you entered. As you use the up and down arrow keys, you are scrolling through the history buffer.
Command history is enabled by default and records ten commands in its history buffer for the current session. How do you edit the number of commands that are stored in the router's history buffer?
To edit the number of command lines stored for the current session, use the terminal history [size number-of-lines] command in privileged EXEC mode. For example, the following changes the history size to 20 lines:
Router#terminal history size 20
On a Cisco router, what does the show version command display?
show version displays the system hardware's configuration, including RAM, Flash memory, software version, configuration register, and boot images:

Router#show version
Cisco Internetwork Operating System Software
IOS (tm) 2500 Software (C2500-D-L), Version 12.0(13), RELEASE
SOFTWARE (fc1)
Copyright (c) 1986-2000 by Cisco Systems, Inc.
Compiled Wed 06-Sep-00 01:08 by linda
Image text-base: 0x030388F8, data-base: 0x00001000

––Text omitted––

Router uptime is 50 minutes
System restarted by power-on
System image file is "flash:c2500-d-l.120-13.bin"

cisco 2505 (68030) processor (revision C) with 8192K/2048K bytes
of memory.
Processor board ID 02073409, with hardware revision 00000000
(text omitted)32K bytes of non-volatile configuration memory.
8192K bytes of processor board System flash (Read ONLY)

Configuration register is 0x2102
On a Cisco router, how do you display the configuration running in RAM?
You display the configuration running in RAM using the show running-config privileged mode command:
Router#show running-config
Building configuration...
Current configuration:
!
version 12.0
service timestamps debug uptime
service timestamps log uptime
!
hostname Router
!
!
--More--
On a Cisco router, how do you view the configuration stored in NVRAM?
You view the configuration stored in NVRAM using the show startup-config privileged mode command.
How do you save the active configuration to nonvolatile RAM (NVRAM)?
To save the running configuration to the startup configuration, use the copy run start privileged mode command.
How do you configure a name on a Cisco router?
The hostname name global configuration command is used to configure a name on a Cisco router. For example, the following command changes the router's host name to RouterA:
Router(config)#hostname RouterA
RouterA(config)#
The hostname name global configuration command is used to configure a name on a Cisco router. For example, the following command changes the router's host name to RouterA:
Router(config)#hostname RouterA
RouterA(config)#
To add a message-of-the-day banner to a Cisco router, enter the banner motd # text # global configuration command. The pound signs (#) are delimiting characters. They can be any character of your choice, but they must be the same and cannot be included in your text. They signify the beginning and end of your text. The following example shows the banner motd command:
RouterA(config)#banner motd # <ENTER>
Enter TEXT message. End with the character '#'.
Warning only authorized users many access this Router. <ENTER>
#
RouterA(config)#
Which of the following is the correct command to add the description "Link to West LA" to an interface on a Cisco router?
A. name Link to West LA
B. interface description Link to West LA
C. description Link to West LA
D. int
C. You add a description to an interface using the description interface-description interface configuration command.
On a Cisco router, how do you set a password to restrict access to privileged EXEC mode?
You set a password to restrict access to privileged EXEC mode using the enable secret global configuration command:
RouterA(config)#enable secret CCNA
This example sets the password to enter privileged mode to CCNA.
On a Cisco router, how do you add a password to the console terminal?
RouterA(config)#line console 0
The login subcommand forces the router to prompt for authentication. Without this command, the router will not authenticate a password. password CCNA sets the console password to CCNA. The password is case-sensitive.
How do you add a password for Telnet access on a Cisco router?
To add a password for Telnet access, enter the line vty 0 4 global configuration command, the login command, and finally the password line subcommand. The password is case-sensitive. In this example, the Telnet password is set to CCNA:
RouterA(config)#line vty 0 4
What command do you use to add a password to the auxiliary interface on your Cisco router?
To add a password to the auxiliary interface, use the aux line number global configuration command, followed by the login and password subcommands, where line number is the number of the auxiliary port you want to add a password to. The password is case-sensitive. The following example sets the password for the auxiliary port to CCNA:
RouterA(config)#aux line 0
When you view the configuration on Cisco routers, only the enable secret password is encrypted. How do you encrypt user mode and the enable password?
To encrypt user mode and the enable password, use the service password-encryption global command:
How do you configure Cisco router interfaces?
To configure an interface on a Cisco router, use the interface interface-type number global configuration command, where interface-type number is the interface type and number you want to configure. For example, if you want to configure the second serial interface on your router, you would enter the following:
RouterA(config)#interface serial1
RouterA(config-if)#
Cisco interfaces start with 0 instead of 1, so the first interface is 0. The prompt also changes to RouterA(config-if)# to tell you that you are in interface mode. If you have a router with a module slot, such as the Cisco 3600, you enter interface mode by entering the slot/port number. For example, if you have a Cisco 3600 router with two module serial interfaces, and you want to configure the first serial interface on the second module, you would enter interface s1/0.
How do you administratively disable an interface on a Cisco router?
You administratively disable an interface on a Cisco router by issuing the shutdown interface configuration command. In this example, the serial interface is issued the shutdown command:
RouterA(config)#int s0
RouterA(config-if)#shutdown
00:27:14: %LINK-5-CHANGED: Interface Serial0, changed state to
What are six of the things the show interface interface-type number command displays?
The show interface command displays the following:
a) Whether the interface is administratively down
b) Whether the line protocol is up or down
c) An Internet address (if one is configured)
d) MTU and bandwidth
e) Traffic statistics on the interface
f) Interface encapsulation type
How do you display the status of interface S0 only?
The IOS command to display the status of interface S0 only is show interface s0.
On your Cisco router, you enter show interface s0 and notice that the port is administratively down. What does this mean, and how do you fix it?
When an interface is administratively down, it was shut down manually or was never enabled at all. To remedy this, enter the interface command no shut.
You are configuring a serial interface, and the interface says "Interface is up, line protocol is down." What does this tell you about the serial interface?
If an interface says "Interface is up, line protocol is down," the interface is experiencing Layer 2 problems. This could be caused by a wrong connector or not receiving keepalives or clocking.
What two commands can you use to show the clock rate on a serial interface?
To view the clock rate on a serial interface, you can use the show running-config privileged EXEC command and the show controllers privileged EXEC command.
Assuming that you are using no CSU/DSU and you are using back-to-back DTE/DCE serial cables, what command would you use to set the serial interface on a router to provide clocking to another router at 64 kbps?
The command to set the serial interface on a router to provide clocking to another router at 64 kbps is clock rate 64000. Setting the clock rate on an interface makes it a DCE interface.
What Cisco IOS router command would you use to find out whether a serial interface is a DCE or DTE interface (providing clocking)?
To see whether a serial interface is providing clocking, use the enable command show controllers serial-interface-type serial-number. The following example shows that serial interface 0 is providing clock rate at 56 kbps:
RouterA#show controllers s 0
HD unit 0, idb = 0xCCE04, driver structure at 0xD2298
buffer size 1524 HD unit 0, V.35 DCE cable, clockrate 56000
cpb = 0x81, eda = 0x4940, cda = 0x4800
RX ring with 16 entries at 0x814800
What is the Cisco Discovery Protocol (CDP)? What layer does in operate on? Is in enabled or disabled by default? What kind of frame does it use?
CDP is a Cisco-proprietary protocol that runs on all Cisco IOS-enabled devices. It gathers information about directly connected neighboring devices. CDP operates at Layer 2 of the OSI model and is media-independent. With CDP, you can tell the hardware type, device identifier, address list, software version, and active interfaces on neighboring Cisco devices. CDP is enabled by default on all Cisco equipment. It uses a nonroutable SNAP frame to communicate between devices.
List five types of information obtained from CDP.
The five types of information obtained from CDP are:
a) Device identifiers (host name of the remote device)
b) Network address list of remote devices
c) Port identifiers of remote devices
d) Capabilities list of remote devices
e) Platform of remote devices (type of remote device)
List four reasons to disable CDP.
Four reasons to disable CDP are:
a) To save network bandwidth by not exchanging CDP frames.
b) To conserve CPU resources on a router if CDP is not required.
c) If you are connecting to non-Cisco devices.
How do you disable CDP on Cisco routers?
Two commands disable CDP on a Cisco router. To disable CDP on the entire device, use the no cdp run global command:
RouterB(config)#no cdp run
To disable CDP on an interface only, use the no cdp enable interface command:
RouterB(config)#int e0
RouterB(config-if)#no cdp enable
This disables CDP on Ethernet interface 0.
What does the show cdp command display?
The show cdp command displays global CDP information about the device. It tells you when the device will send CDP packets and the CDP holdtime:
RouterB#show cdp
Global CDP information:
Sending CDP packets every 60 seconds
Sending a holdtime value of 180 seconds
On a Cisco router, what does the show cdp neighbors command display?
The show cdp neighbors command displays the following:
a) Device ID (name of the device)
b) The local interface (local outgoing port)
c) The holdtime in seconds
d) The device's capability code
e) Hardware platform of the neighboring device
f) Port ID of the neighboring device (remote port)
Here is some sample output from this command:
Not on the CD but only on paper.
What 6 items does the show cdp neighbors detail command display?
The show cdp neighbors detail and show cdp entry * commands show the same output. They both display the following:
a) Device ID (host name) of the remote neighbor
b) Layer 3 address of the remote device (if the device has more than one Layer 3 address on its interface, only the primary address is shown)
c) Device platform and capabilities
d) Local interface and outgoing port ID
e) Remote device holdtime in seconds
f) IOS type and version
What does the show cdp traffic command display?
The show cdp traffic command displays information about interface traffic. This includes the number of CDP packets sent and received and CDP errors:
RouterB#show cdp traffic
CDP counters :

Hdr syntax: 0, Chksum error: 0, Encaps failed:
No memory: 0, Invalid packet: 0, Fragmented: 0
What does the show cdp interface command display?
The show cdp interface command displays the status of CDP on all interfaces on your device:

RouterB#show cdp interface
Ethernet0 is up, line protocol is down
Encapsulation ARPA
Sending CDP packets every 60 seconds
Holdtime is 180 seconds
Serial0 is up, line protocol is up
Encapsulation HDLC
Sending CDP packets every 60 seconds
Holdtime is 180 seconds
Serial1 is up, line protocol is up
Encapsulation HDLC
Sending CDP packets every 60 seconds
Holdtime is 180 seconds
What Cisco IOS router command can you use to see a neighbor router's IP address?
To see a neighbor router's IP address, you must use the show cdp neighbor detail or show cdp entry * user mode or EXEC command.
What IOS command shows the active outbound connections after you Telnet into multiple routers simultaneously?
The show sessions command displays the active outbound Telnet sessions from that particular user on your router:
RouterA#show sessions
Conn Host Address Byte Idle Conn Name
* 1 192.168.1.2 192.168.1.2 0 0 192.168.1.2
What key sequence do you use to suspend a Telnet session on a remote system and return to your local router?
To suspend a Telnet session, press Ctrl-Shift-6 and then press X.
How do you reestablish a suspended Telnet session on a Cisco router?
To reestablish a suspended Telnet session, use the show session command to find the session you want to resume, and then use the resume session-number command to connect to the specified session:
RouterA#show session
Conn Host Address Byte Idle Conn Name
1 192.168.1.2 192.168.1.2 0 0 192.168.1.2
* 2 192.168.2.2 192.168.2.2 0 0 192.168.2.2

RouterA#resume 1
[Resuming connection 1 to 192.168.1.2 ... ]

RouterB>
How do you end a remote Telnet session on a Cisco router?
To end a Telnet session, use the exit or logout command while you're on the remote device:
RouterB>exit

[Connection to 192.168.1.2 closed by foreign host]
RouterA#
Upon using the ping EXEC command, you can receive the following responses:
.
!
?
C
U
I
What does each of these responses mean?
The following table from Cisco Systems' website describes what each character means with the ping command.

Char Description
. Each period indicates that the network server timed out while waiting for a reply.
! Each exclamation point indicates the receipt of a reply.
? Unknown packet type.
C A congestion experienced packet was received.
U A destination unreachable error PDU was received.
I The user interrupted the test.
What is the trace EXEC command used for?
The trace EXEC command displays the path a packet used to get to a remote device:
RouterA#trace 192.168.2.2

Type escape sequence to abort.
Tracing the route to 192.168.2.2

1 192.168.2.2 16 msec 16 msec *
What two Cisco IOS commands verify end-to-end connectivity?
The two Cisco IOS commands that verify end-to-end connectivity are the ping and trace EXEC commands. The ping command sends an echo to the remote destination; the trace command shows the path from the source to the destination.
What are the two ways in which a Cisco router resolves host names to IP addresses?
A Cisco router resolves host names using either a DNS server or a locally configured host table on each router.
Which router component stores the routing tables, packet buffers, and ARP cache?
RAM holds the router's routing table, packet buffers, and ARP cache. The running-config is also stored in RAM. On most Cisco routers, the IOS is loaded into RAM as well.
What is the function of ROM on a Cisco router?
On a Cisco router, ROM starts and maintains the router.
What is Flash memory used for on a Cisco router? Is it or is it not erased when the router or switch is reloaded?
Flash memory stores the Cisco IOS software image and, if there is room, multiple configuration files or multiple IOS files. On some routers (the 2500 series), it is also used to run the IOS. Flash memory is not erased when the router or switch is reloaded.
What is the function of NVRAM on a Cisco router?
Nonvolatile random-access memory (NVRAM) is used to hold the saved router configuration (and the switch configuration). This config is maintained when the device is turned off or reloaded.
What is the main purpose of the configuration register on a Cisco router? What is its length? How, in terms of functions, is it defined by default?
The configuration register's main purpose is to control how the router boots up. It is a 16-bit software register that by default is set to load the Cisco IOS from Flash memory and to look for and load the startup-config file from NVRAM.
What Cisco IOS command would you use to view the current configuration register value?
The show version command is used to display the router's current configuration register:
RouterA#show version
Cisco Internetwork Operating System Software
IOS (tm) 2500 Software (C2500-D-L), Version 12.0(13),
RELEASE SOFTWARE (fc1)
Copyright (c) 1986-2000 by cisco Systems, Inc.
Compiled Wed 06-Sep-00 01:08 by linda
Image text-base: 0x030388F8, data-base: 0x00001000
<Output omitted>
Configuration register is 0x2102
How do you change the configuration register on a Cisco router?
To change the configuration register on a Cisco router, use the config-register command in global configuration mode.
Where would the router boot from if the configuration register settings were changed to 0x0101?
The router would boot from ROM if you changed the configuration register setting to 0x0101.
What Cisco IOS command displays the contents of Flash memory? What else does this command diplay?
The show flash command displays the contents of Flash memory. This includes the images stored in Flash memory, the images' names, bytes used in Flash memory, bytes available, and the total amount of Flash memory on your router:
RouterA#show flash

System flash directory:
File Length Name/status
1 6897716 c2500-d-l.120-13.bin
[6897780 bytes used, 1490828 available, 8388608 total]
8192K bytes of processor board System flash (Read ONLY)
What IOS command configures the router to boot from an alternative IOS located in Flash?
The boot system flash ios-file-name global configuration command instructs the router to boot from a different IOS located in Flash memory.