Cisco Exam #640-801: CCNA (MeasureUp, set 2)
Test your basic networking knowledge for Cisco's entry-level certification exam with these 15 questions and answers.
courtesy of MeasureUp
Question:
1. Which addresses can be given to devices in network 131.107.0.0 with a standard Class B subnet mask? (Choose three.)
a. 131.107.255.0
b. 131.107.0.255
c. 131.107.255.255
d. 131.107.1.0
e. 131.107.0.0
2. Given the IP address 130.113.64.17/24, which statement is true?
a. 130.113.64.0 is the network number.
b. 130.113.0.0 is the network number.
c. 130.0.0.0 is the network number.
d. 255.255.0.0 is the subnet mask.
3. SNMP uses which Transport layer port number to communicate?
a. UDP port 21
b. TCP port 21
c. TCP port 23
d. UDP port 69
e. UDP port 161
f. TCP port 161
4. Given a configuration register value of 0x2102, select the invalid router boot sequence command.
a. boot system tftp IOS_filename tftp_address
b. boot system rom
c. boot system nvram
d. boot system flash IOS_filename
5. Which answer best describes the function of ICMP?
a. ICMP is a distance vector routing protocol.
b. ICMP provides control and messaging capabilities.
c. ICMP provides hostname to IP address resolution.
d. ICMP determines the Data Link layer address from known IP addresses.
6. Which descriptions are characteristics of Fast Ethernet? (Choose two.)
a. It supports auto negotiation.
b. It supports full-duplex operation.
c. It operates at 1000Mbps.
d. It creates its own broadcast domain.
e. It uses only two conductors in an Ethernet patch cable.
7. Which terms are used to refer to a Layer two address? (Choose two.)
a. BIA
b. Sequence Number
c. OUI
d. Logical
e. Port number
8. What are characteristics of a full-duplex Ethernet connection? (Choose three.)
a. Collision detection is disabled.
b. Collisions cannot occur.
c. Hubs support full-duplex.
d. It improves bandwidth.
e. It decreases the number of broadcast domains.
9. What is the most common Layer 2 device?
a. router
b. switch
c. repeater
d. gateway
10. Which configuration register setting will cause the router to boot from ROM (RXBOOT)?
a. 0x2102
b. 0x2101
c. 0x1000
d. 0x0107
11. Which statement is true of fragment-free switching?
a. It performs error checking on the first 64 bytes of the frame.
b. It will read the entire frame before making the switching decision.
c. It provides for more latency than Store-and-forward switching.
d. It has the same latency as Store-and-forward switching.
e. It is the typical switching mode for most switches.
12. Which switching method has the worst latency?
a. Store-and-forward
b. Cut-Through
c. Fragment-Free
d. Modified Cut-Through
13. Which three standards correspond to Layer 2 of the OSI reference model? (Choose three.)
a. IEEE 802.2
b. LAPB
c. Frame-Relay
d. EIA/TIA 100BaseTX
e. HTTP
f. FTP
g SQL
14. TFTP uses which transport protocol?
a. SPX
b. UDP
c. ICMP
d. TCP
15. What are the benefits of LAN segmentation? (Choose two.)
a. a decrease in WAN costs
b. an increase in collision domains
c. fewer network addresses
d. an increase in bandwidth per user
e. larger shared media segments
1. A, B and D are correct. The IP address given, 131.107.0.0, is a Class B network which has a default subnet mask of 255.255.0.0. The subnet mask used in this problem is 255.255.0.0, which means that you have 16 network bits (/16) total and 16 host bits. Therefore, this network is not subnetted.
If you converted this subnet mask to binary, you would have the binary number:
11111111.11111111.00000000.00000000
To determine the number of subnets, use the 2^N-2 formula on the number of subnet bits (0). This yields zero subnets.
To calculate the range of host addresses per network, use the 2^N-2 formula on the number of host bits (16). This yields:
65536 - 2 = 65534 (hosts per subnet)
The IP address in the question, 131.107.0.0, would therefore fall in the range between 131.107.0.0 and 131.107.255.255. There are 65534 usable IP addresses in this range. You cannot use the first, 131.107.0.0, because this is the network number itself. This number cannot be assigned to a host. The last number in this subnet is 131.107.255.255, but this cannot be assigned to a host because this is the broadcast for the network. That leaves you with the first usable IP address of 131.107.0.1, and all addresses between it and the broadcast are valid. The highest host number then would be 131.107.255.254.
2. A is correct. The network layer (Layer 3) handles network addressing and decides the best path through a network. Layer 3 of the Open Systems Interconnect (OSI) model defines the network or logical addressing of packets. At this layer, segments are converted to datagrams or packets.
Internet protocol (IP) addresses are 32 bits long and are divided into four octets (divisions of 8 bits each). They consist of two parts:
- The Network Portion - This part is similar to a street name. There are many houses on a street.
- The Host Portion - This part is similar to the house number on the street.
Subnet masks tell you what portion of the IP address is the Network and which part is the Host address. For example:
130.113.64.17
255.255.255.0
In binary, the mask would look like this:
11111111.11111111.11111111.00000000
Wherever there are 1s in the subnet mask, the corresponding bits in the IP address are the network portion of the address. Wherever there are binary 0s in the subnet mask, the corresponding bits in the IP address are the host portion of the address.
If you are given a subnet mask of 255.255.255.0 and an IP address of 130.113.64.17, the network portion (based on the mask) would be 130.113.64 and the host portion would be .17. Therefore, the network's IP address is 130.113.64.0 because a host of .0 indicates that this is the network's address.
3. E is correct. Simple Network Management Protocol (SNMP) is an Application layer-passive protocol that handles Management Information Block (MIB) queries by sending out User Datagram Protocol (UDP) responses. The requester interrogates the SNMP capable Router (a string called an OID), and the router responds with the information requested. It sounds connection-oriented, but it's actually a series of UDP conversations.
TCP/IP allows multiple, simultaneous, data flows by a process called multiplexing. Multiplexing allows FTP, Telnet, SMTP, and other protocols to operate at the same time. The data packets are separated at the Transport layer using different port numbers to identify the process.
There are 65,536 ports. The first 1024 are known as the well-known port numbers, and the most popular protocols are assigned a port in this range.
When an application attempts to connect to a remote host, it uses a random source port known as the ephemeral port number. It is typically a port number above 1023.
Servers listen on the well-known ports. For servers to identify the connection attempt, the destination port needs to be a port number that is known.
The following is a partial list of well-known ports:
- Port 21 - FTP, which uses TCP
- Port 23 - Telnet, which uses TCP
- Port 25 - SMTP, which uses TCP
- Port 53 - DNS, which uses UDP
- Port 69 - TFTP, which uses UDP
- Port 80 - HTTP, which uses TCP
- Port 161 - SNMP, which uses UDP
4. C is correct. The configuration register is a 16-bit software register in the router. The boot field is the name of the low-order 4 bits of the configuration register. The 4-bit blocks in the register are represented by hexadecimal numbers. The default value of the configuration register is 0x2102. The hexadecimal 2 on the right end is 0010 in binary and is known as the boot field. Setting the value of the boot field controls where the router will select its IOS image on next reload. If the boot field value is...
- 0 - Router boots to ROM Monitor Mode.
- 1 - Router boots from IOS in ROM (RX-Boot Mode).
- Any other value - Router will first look in FLASH for an Internetwork Operating System (IOS).
If no IOS is found there, the router will look for a TFTP server with an IOS image to load. If it fails to find an IOS on a TFTP server, it will boot from the limited feature IOS in ROM, and if that fails, it will boot from ROM Monitor mode.
This boot sequence can be modified using the "boot system" global command.
The configuration register determines the location of the source files to boot the router.
"boot system nvram" is an invalid route boot sequence command because the IOS cannot be loaded from NVRAM. NVRAM is too small to contain IOS software.
All other commands are valid commands.
"boot system rom" instructs the router to boot from ROM. This is known as "RXBOOT".
"boot system flash IOS_filename" instructs the router to boot from flash using the filename specified by the IOS_filename variable.
"boot system tftp IOS_filename tftp_address" instructs the router to boot from a TFTP server at the IP address specified by the tftp_address variable using the filename specified by the IOS_filename variable.
The boot system commands are executed in the order in which they are configured. The "boot" command line syntax is shown here:
Boot Options:
- router(config)#boot ?
- bootstrap Bootstrap image file
- buffersize Specify the buffer size for netbooting a config file
- host Router-specific config file
- network Network-wide config file
- system System image file
Boot System Options:
- router(config)#boot system ?
- WORD TFTP filename or URL
- flash Boot from flash memory
- mop Boot from a DECNet MOP server
- rcp Boot from a server via rcp
- rom Boot from rom
- tftp Boot from a tftp server
To boot from ROM, use either "boot system rom" or "boot system flash bootflash" commands.
To boot from flash, use "boot system flash filename" command or simply "boot system flash".
To boot from a TFTP server, use the command "boot system tftp filename ipaddress".
For any of these commands to work, the configuration register boot field must be set to 0x2 or higher. These commands are issued while in global config mode.
5. B is correct. ICMP (Internet Control Message Protocol) provides control and messaging capabilities. Internet Control Message Protocol (ICMP) is used to help manage and control the operation of a TCP/IP network. It provides a wide variety of information about the health and operational status of a network. The ICMP messages are inside an IP packet, with no Transport layer header at all, so it is truly just an extension of the TCP/IP Network layer.
Examples of ICMP messages are: Destination unreachable, TTL exceeded, and Redirect. Also included as part of ICMP is the troubleshooting tool PING (echo request and echo reply).
Domain Name Service (DNS) provides hostname to IP address resolution.
Routing Information Protocol (RIP) and Interior Gateway Routing Protocol (IGRP) are examples of distance vector routing protocols.
Address Resolution Protocol (ARP) determines the Data Link layer address for known IP addresses.
6. A and B are correct. Fast Ethernet is a networking technology that supports data transfer rates up to 100 Megabits per second (Mbps). It supports full-duplex operation, which allows the collision detection circuitry to be disabled since no collisions are possible. Gigabit Ethernet can operate up to 1000Mbps. 100Base-T (Fast Ethernet) is the IEEE 802.3u standard.
Fast Ethernet's characteristics include support for a bandwidth of 100 Mbps, support for full-duplex operation, and speed auto negotiation. Auto negotiation allows the circuitry to automatically determine the speed of other devices on the LAN and match its speed with the other.
Fast Ethernet does not create broadcast domains. Only routers and VLANs separate broadcast domains.
Fast Ethernet uses four conductors in an Ethernet patch cable.
7. A and C are correct. Layer 2 addressing uses Media Access Control (MAC) addresses. A MAC address is made up of two other numbers, the BIA and OUI.
OUI (Organizationally Unique Identifier) is the first 24-bits (first half) of a MAC address. It identifies the manufacturer of the circuit card.
BIA (Burned in Address) is the last half of the MAC address. It is burned into the ROM on most network interface cards. Although this address refers to the physical NIC (network interface card), it is still a Layer 2 address. The manufacturer assigns this number to ensure it is unique in the world.
Logical refers to the Network layer (Layer 3) address. IP addresses are logical addresses.
Sequence Numbers are relevant to the Transport layer (Layer 4). They are used in the TCP header.
Port number refers to the Transport layer TCP and UDP ports.
8. A, B and D are correct. Full Duplex operation uses simultaneous send and receive channels. On a full-duplex Ethernet connection, the transmit circuit at each end is connected directly to the receive circuit at the opposite end. Collisions cannot occur.
Hosts connected to a hub cannot use the full-duplex operation mode, because hubs rely on collision detection to allow host access to the wire. For full-duplex to work, collision detection must be disabled. Switches support full-duplex.
Full-duplex effectively doubles bandwidth because it permits sending and receiving data simultaneously.
Your network infrastructure must be capable of supporting full-duplex communications. Network designs that incorporate a switched backbone are capable of supporting this type of communication.
Full-duplex has no effect on broadcast domains. Routers divide broadcast domains.
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9. B is correct. Bridges and Switches operate at Layer 2 (Data Link layer). They use the MAC address of the frames to make forwarding decisions.
Routers operate at the Network layer, Layer 3. Routers make routing decisions based on the logical address in the Layer 3 header.
Repeaters only boost the signal and retransmit it; they don't get involved with the packet's content. Repeaters work at Layer 1, the Physical layer.
Gateways operate at Layers 4 through 7. This does not refer to the default gateway that separates a LAN from the next network. A gateway is software built into the network operating system (NOS) that allows one NOS to connect to another.
10. B is correct. If the configuration register is set to 0x2101, the router will boot from ROM into RXBOOT mode on the next reboot.
The configuration register is a 16-bit software register in the router. The boot field is the name of the low-order 4 bits of the configuration register. The 4-bit blocks in the register are represented by hexadecimal numbers. The default value of the configuration register is 0x2102. The hexadecimal 2 on the right end is 0010 in binary and is known as the boot field. Setting the value of the boot field controls where the router will select its Internetwork Operating System (IOS) image on next reload. If the boot field value is...
-
0 - Router boots to ROM Monitor Mode (ROMMON).
-
1 - Router boots from IOS in ROM (RX-Boot Mode).
-
Any other value - Router will first look in FLASH for an IOS.
If no IOS is found there, the router will look for a TFTP server with an IOS image to load. If it fails to find an IOS on a TFTP server, it will boot from the limited feature IOS in ROM (RXBOOT), and if that fails, it will boot from ROM Monitor mode.
This boot sequence can be modified using the "boot system" global command.
The default value for the configuration register is 0x2102. The boot field is 2 (the last 2). With this setting, the router boots normally.
If the configuration register is 0x1000, the boot field value is zero (the last 0), so it will boot to ROMMON.
If the configuration register is 0x0107, the boot field is 7 so the router will still boot normally.
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11. A is correct. Switches use several different processing methods to make switching decisions.
Fragment-free switching provides a speed compromise between Store-and-forward and cut-through switching in terms of latency. It performs like cut-through, but waits for the first 64 bytes of the frame to be received, makes the switching decision, and begins forwarding the frame even before receiving the entire frame. It uses the logic that collisions should be detected within the first 64 bytes of a frame. If a collision has not been detected by then, the frame is considered okay. The only limitation is that it does not have an opportunity to check the Frame Check Sequence (FCS), which is in the trailer of the frame, before forwarding the frame.
The Store-and-forward switching mode receives the complete frame before forwarding takes place. After the destination and source addresses are read, the cyclic redundancy check is performed and the frame is forwarded.
Cut-through switching begins its switching decision immediately after identifying the destination MAC address of the frame. Once the forwarding decision has been made, even if the frame has not been received in its entirety, the switch begins forwarding the frame. This allows the switch to forward frames with minimal latency, but prevents the switch from performing a cyclic redundancy check (error checking).
It is important to remember that fragment-free only provides error checking on the first 64 bytes of packet, so even if an error is present after the 64th byte, it will still be considered a valid packet. Conversely, if the switch examines the packet and finds it to be less than 64 bytes in size (otherwise known as a runt), it will discard it completely. Therefore, if the switch does not detect an error in the preamble, the frame will be forwarded.
Collisions usually occur within the first 64 bytes of the frame. This is the reason that fragment-free switching mode is capable of forwarding at a much higher rate than Store-and-forward. It doesn't have to read the entire frame before making a decision about forwarding the packet. Therefore, fragment-free switching has less latency than Store-and-forward switching.
Finally, most of the modern switches use Store-and-forward switching, but all three types are available in one product or another.
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12. A is correct. Switches use several different processing methods to make switching decisions.
With Store-and-forward, the switch receives the entire frame before making a switching decision. After the destination and source addresses are read and the cyclic redundancy check is performed, the frame is forwarded. This allows the switch to perform error checking before forwarding, but increases the latency with the size of the frame.
Cut-through switching begins its switching decision immediately after identifying the destination MAC address of the frame. Once the forwarding decision has been made, even if the frame has not been received in its entirety, the switch begins forwarding the frame. This allows the switch to forward frames with minimal latency, but prevents the switch from performing a cyclic redundancy check (error checking).
Fragment-free switching provides a speed compromise between Store-and-forward and cut-through switching in terms of latency. It performs like cut-through, but waits for the first 64 bytes of the frame to be received, makes the switching decision, and begins forwarding the frame even before receiving the entire frame. It uses the logic that collisions should be detected within the first 64 bytes of a frame. If a collision has not been detected by then, the frame is probably okay. The only limitation is that it does not have an opportunity to check the Frame Check Sequence (FCS), which is in the trailer of the frame, before forwarding the frame.
It is important to remember that fragment-free only provides error checking on the first 64 bytes of packet, so even if an error is present after the 64th byte, it will still be considered a valid packet. Conversely, if the switch examines the packet and finds it to be less than 64 bytes in size (otherwise known as a runt), it will discard it completely. Therefore, if the switch does not detect an error in the preamble, the frame will be forwarded. Collisions usually occur within the first 64 bytes of the frame. This is the reason that fragment-free switching mode is capable of forwarding at a much higher rate than Store-and-forward. It doesn't have to read the entire frame before making a decision about forwarding the packet. Therefore, fragment-free switching has less latency than Store-and-forward switching.
Finally, most of the modern switches use Store-and-forward switching, but all three types are available in one product or another. Modified cut-through is just another name for fragment-free.
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13. A, B and C are correct. IEEE 802.2 is defined at the Data Link layer (layer 2). This specification, Logical Link Control (LLC), is the higher of the two sublayers of the Data Link layer. LLC provides error detection (but not correction), flow control, framing, and software-sublayer addressing.
Frame-relay, a Wide Area Network (WAN) standard, is a packet-switched Data Link layer (layer 2) standard that uses multiple virtual circuits and Link Access Procedure for Frame Mode Bearer Services (LAPF) encapsulation between connected devices.
Link Access Procedure, Balanced (LAPB), the Data Link layer (layer 2) implementation of X.25 WAN standards, allows both sides of a WAN link, the Data Terminal Equipment (DTE) and the Data Communications Equipment (DCE), to initiate communication with the other. During information transfer, LAPB checks that the frames arrive at the receiver in the correct sequence and error-free.
The Electronic Industries Association/Telecommunications Industry Alliance (EIA/TIA) standards are hardware standards that define the physical characteristics of network cabling. It is a Physical layer (Layer 1) standard.
Hypertext Transfer Protocol (HTTP) and File Transfer Protocol (FTP) are Application layer (Layer 7) protocols.
Structured Query Language (SQL) is a Session layer (Layer 5) protocol used for database management over a network.
14. B is correct. Trivial File Transfer Protocol (TFTP) uses the connectionless transport protocol, User Datagram Protocol (UDP), which uses port 69. UDP is used for basic file transfer, such as installing a new router operating system. Applications that use the connectionless service of UDP include:
-
Domain Name Service (DNS)
-
Dynamic Host Configuration Protocol (DHCP)
-
Trivial File Transfer Protocol (TFTP)
-
Simple Network Management Protocol (SNMP)
Transmission Control Protocol (TCP) provides reliable data transfer and flow-controlled service to upper-layer protocols. The following list of Application layer protocols use the connection-oriented service of TCP:
-
File Transfer Protocol (FTP)
-
Telnet
-
Simple Mail Transfer Protocol (SMTP)
-
Post Office Protocol 3 (POP3)
-
Hypertext Transfer Protocol (HTTP)
Internet Control Message Protocol (ICMP), an Internet protocol that works at the Network layer, reports errors and provides other information relevant to IP packet processing.
Sequenced Packet Exchange (SPX), a NetWare transport protocol, is a reliable, connection-oriented protocol. It is a Transport layer protocol that supports the NetWare core protocols and supplements the datagram service provided by Network layer (Layer 3) protocols.
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15. B and D are correct. When a Local Area Network (LAN) is segmented, each segment becomes a separate collision domain. With multiple collision domains, fewer users are in each one, and therefore have less competition for the bandwidth on that segment.
By segmenting, you are creating smaller (not larger) shared media segments. Since you have not reduced the total number of users, you do not have fewer addresses.
Segmenting a network requires additional hardware, such as bridges, switches, or routers and if anything, increases LAN costs, but has no effect on Wide Area Network (WAN) costs.
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