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Network A system of interconnected computers and computerized peripherals such as printers is called computer network. This interconnection among computers facilitates information sharing among them. Computers may connect to each other by either wired or wireless media. A computer network consists of a collection of computers, printers and other equipment that is connected together so that they can communicate with each other.  

Network application
A Network application is any application running on one host and provides a communication to another application running on a different host, the application may use an existing application layer protocols such as: HTTP(e.g. the Browser and web server), SMTP(e.g. the email-client). And may be the application does not use any existing protocols and depends on the socket programming to communicate to another application. So the web application is a type of the network applications. 
There are lots of advantages from build up a network, but the th…

Answers to Review Questions

1. A. The device shown is a hub and hubs place all ports in the same broadcast domain 
Image result for review questions"
and the same collision domain.
2. B. The contents of a protocol data unit (PDU) depend on the PDU as they are created 
in a specific order and their contents are based on that order. A packet will contain 
IP addresses but not MAC addresses as MAC addresses are not present until the PDU 
becomes a frame. 
3. C. You should select a router to connect the two groups. When computers are in different subnets, as these two groups are, you will require a device that can make decisions 
based on IP addresses. Routers operate at layer 3 of the Open Systems Interconnect 
(OSI) model and make data-forwarding decisions based on layer 3 networking information, which are IP addresses. They create routing tables that guide them in forwarding traffic out of the proper interface to the proper subnet.
4. C. Replacing the hub with a switch would reduce collisions and re-transmissions which 
would have the most impact on reducing congestion.
5. Answer:
Layer Description
Transport Bits
Data Link Segment
Physical Packet
Network Frame

The given layers of the OSI model use the PDUs shown in the above diagram.
6. C. The diagram depicts the three steps taken to create a TCP connection.
7. B. You should use a switch to accomplish the task in this scenario. A switch is used to 
provide dedicated bandwidth to each node by eliminating the possibility of collisions 
on the switch port where the node resides. Switches work at layer 2 in the Open System 
Interconnection (OSI) model and perform the function of separating collision domains.
Data Link
End-to-end connection
Conversion to bits
The listed layers of the OSI model have the functions shown in the diagram above.
9. D. Reliable data delivery ensures the integrity of a stream of data sent from one 
machine to the other through a fully functional data link. It guarantees that the 
data won’t be duplicated or lost. This is achieved through something called positive 
acknowledgment with retransmission—a technique that requires a receiving machine 
to communicate with the transmitting source by sending an acknowledgment message, 
based on the window size, back to the sender when it receives data.
10. B. Protocols used to support data traffic are called routed protocols and some key 
examples of them include IP and IPv6.
11. B. Data translation and code formatting occur on the Presentation layer of the 
OSI model.
12. C. The IEEE Ethernet Data Link layer has two sublayers, the Media Access Control 
(MAC) and the Logical Link Control (LLC).
13. B. Windows are used to control the amount of outstanding, unacknowledged data segments. In the diagram, a windows size of three has been agreed upon by the stations.
14. A. Hubs operate on the Physical Layer as they have no intelligence and send all traffic 
in all directions. 
15. C. While it is true that the OSI model’s primary purpose is to allow different vendors’ 
networks to interoperate, there is no requirement that any vendor follows the model. 
16. A. Routers by default do NOT forward broadcasts.
17. C. Switches create separate collision domains within a single broadcast domain. Routers 
provide a separate broadcast domain for each interface. 
18. B. The all-hub network at the bottom is one collision domain; the bridge network 
on top equals three collision domains. Add in the switch network of five collision 
domains—one for each switch port—and you get a total of nine.
19. A. The top three layers define how the applications within the end stations will communicate with each other as well as with users.
20. A. The following network devices operate at all seven layers of the OSI model: network 
management stations (NMSs), gateways (not default gateways), servers and network hosts.
990 Appendix B u Answers to Review Questions
Chapter 2: Ethernet Networking and 
Data Encapsulation
1. D. The organizationally unique identifier (OUI) is assigned by the IEEE to an organization composed of 24 bits, or 3 bytes, which in turn assigns a globally administered 
address also comprised of 24 bits, or 3 bytes, that’s supposedly unique to each and 
every adapter it manufactures.
2. A. Back-off on an Ethernet network is the retransmission delay that’s enforced when a collision occurs. When that happens, a host will only resume transmission after the forced time delay has expired. Keep in mind that after the back-off has elapsed, all stations have equal priority to transmit data.
3. A. When using a hub all ports are in the same collision domain which will introduce collisions as shown between devices connected to the same hub.
4. B. FCS is a field at the end of the frame that’s used to store the cyclic redundancy check 
(CRC) answer. The CRC is a mathematical algorithm that’s run when each frame is built based on the data in the frame. When a receiving host receives the frame and runs the CRC, the answer should be the same. If not, the frame is discarded, assuming errors have occurred.
5. B. Ethernet networking uses a protocol called Carrier Sense Multiple Access with Collision Detection (CSMA/CD), which helps devices share the bandwidth evenly, while preventing two devices from transmitting simultaneously on the same network medium
6. D. Hubs are not capable of providing a full-duplex connection.
7. D. The cable shown is a straight-through cable which is used between dissimilar devices. 
8. B, C. The high-order bit is the Individual/Group (I/G) bit. When it has a value of 0, we can assume that the address is the MAC address of a device and that it may well appear in the source portion of the MAC header. When it’s a 1, we can assume that the 
address represents either a broadcast or multicast address in Ethernet.
9. B. In creating the gigabit crossover cable, you’d still cross 1 to 3 and 2 to 6, but you would add 4 to 7 and 5 to 8.
10. D. When you set up the connection, use these settings:
 Bits per sec: 9600
 Data bits: 8
 Parity: none
 Stop bits: 1
 Flow control: none
Chapter 3: Introduction to TCP/IP 991
11. D. When set to 0, this bit represents a globally administered address, as by the IEEE, but when it’s a 1, it represents a locally governed and administered address.
12. B. You can use a rolled Ethernet cable to connect a host EIA-TIA 232 interface to a router console serial communication (COM) port.
13. B. The collision will invoke a back-off algorithm on all systems, not just the ones involve in the collision.
14. A. There are no collisions in full-duplex mode.
15.B. The connection between the two switches requires a crossover and the connection from the hosts to the switches required a straight through.
16. The given cable types are matched with their standards in the diagram below.
IEEE 802.3u 100Base-Tx
IEEE 802.3 10Base-T
IEEE 802.3ab 1000Base-T
IEEE 802.3z 1000Base-SX
The given cable types are matched with their standards in the diagram above.
17. B. Although rolled cable isn’t used to connect any Ethernet connections together, you can use a rolled Ethernet cable to connect a host EIA-TIA 232 interface to a router console serial communication (COM) port.
18. B. If you’re using TCP, the virtual circuit is defined by the source and destination port 
number plus the source and destination IP address and called a socket.
19. A. The hex value 1C is converted as 28 in decimal.
20. A. Fiber optic cables are the only ones that have a core surrounded by a material called cladding.
Chapter 3: Introduction to TCP/IP
1. C. If a DHCP conflict is detected, either by the server sending a ping and getting a response or by a host using a gratuitous ARP (arp’ing for its own IP address and seeing 
if a host responds), then the server will hold that address and not use it again until it is 
fixed by an administrator.
2. B. Secure Shell (SSH) protocol sets up a secure session that’s similar to Telnet over a standard TCP/IP connection and is employed for doing things like logging into systems, running programs on remote systems, and moving files from one system to another.
992 Appendix B u Answers to Review Questions
3. C. A host uses something called a gratuitous ARP to help avoid a possible duplicate 
address. The DHCP client sends an ARP broadcast out on the local LAN or VLAN 
using its newly assigned address to solve conflicts before they occur.
4. B. Address Resolution Protocol (ARP) is used to find the hardware address from a 
known IP address.
5. A, C, D. The listed answers are from the OSI model and the question asked about the TCP/IP protocol stack (DoD model). Yes, it is normal for the objectives to have this type of question. However, let’s just look for what is wrong. First, the Session layer is not in the TCP/IP model; neither are the Data Link and Physical layers. This leaves us with the Transport layer (Host-to-host in the DoD model), Internet layer (Network layer in the OSI), and Application layer (Application/Process in the DoD). Remember, the CCENT objectives can list the layers as OSI layers or DoD layer at any time, regardless of what the question is asking.
6. C. A Class C network address has only 8 bits for defining hosts: 28 – 2 = 256.
7. A, B. A client that sends out a DHCP Discover message in order to receive an IP address sends out a broadcast at both layer 2 and layer 3. The layer 2 broadcast is all Fs in hex, or FF:FF:FF:FF:FF:FF. The layer 3 broadcast is, which means any networks and all hosts. DHCP is connection-less, which means it uses User Datagram Protocol (UDP) at the Transport layer, also called the Host-to-host layer.
8. B. Although Telnet does use TCP and IP (TCP/IP), the question specifically asks about layer 4, and IP works at layer 3. Telnet uses TCP at layer 4.
9. RFC 1918 These addresses can be used on a private network, but they’re not routable through the Internet.
10. B, D, E. SMTP, FTP, and HTTP use TCP.
11. C. Class C addresses devote 24 bits to the network portion and 8 bits to the host portion.
12. C. The range of multicast addresses starts with and goes through
13. C. First, you should know easily that only TCP and UDP work at the Transport layer, so now you have a 50/50 shot. However, since the header has sequencing, acknowledgment, and window numbers, the answer can only be TCP.
14. A. Both FTP and Telnet use TCP at the Transport layer; however, they both are Application layer protocols, so the Application layer is the best answer for this question.
15. C. The four layers of the DoD model are Application/Process, Host-to-Host, Internet, and Network Access. The Internet layer is equivalent to the Network layer of the OSI model.
Chapter 4: Easy Subnetting 993
16. C, E. The Class A private address range is through The Class B private address range is through, and the Class C private address range is through
17. B. The four layers of the TCP/IP stack (also called the DoD model) are Application/Process, Host-to-host, Internet, and Network Access. The Host-to-host layer is equivalent to the Transport layer of the OSI model.
18. B, C. ICMP is used for diagnostics and destination unreachable messages. ICMP is encapsulated within IP datagrams, and because it is used for diagnostics, it will provide hosts with information about network problems.
19. C. The range of a Class B network address is 128–191. This makes our binary range 
DHCPOffer TargetB
DHCPDiscover TargetA
DHCPAck TargetD
DHCPRequest TargetC
The steps are as shown in the answer diagram.
Chapter 4: Easy Subnetting
1. D. A /27 ( is 3 bits on and 5 bits off. This provides 8 subnets, each with 30 hosts. Does it matter if this mask is used with a Class A, B, or C network address? Not at all. The number of host bits would never change.
2. D. A 240 mask is 4 subnet bits and provides 16 subnets, each with 14 hosts. We need more subnets, so let’s add subnet bits. One more subnet bit would be a 248 mask. This provides 5 subnet bits (32 subnets) with 3 host bits (6 hosts per subnet). This is the best answer.
3. C. This is a pretty simple question. A /28 is, which means that our block size is 16 in the fourth octet. 0, 16, 32, 48, 64, 80, etc. The host is in the 64 subnet.
4. F. A CIDR address of /19 is This is a Class B address, so that is only 3 subnet bits, but it provides 13 host bits, or 8 subnets, each with 8,190 hosts.
994 Appendix B u Answers to Review Questions
5. B,D The mask (/23) used with a Class A address means that there are 15 subnet bits and 9 host bits. The block size in the third octet is 2 (256 – 254). So this makes the subnets in the interesting octet 0, 2, 4, 6, etc., all the way to 254. The host is in the 2.0 subnet. The next subnet is 4.0, so the broadcast address for the 2.0 subnet is 3.255. The valid host addresses are 2.1 through 3.254.
6. D. A /30, regardless of the class of address, has a 252 in the fourth octet. This means we have a block size of 4 and our subnets are 0, 4, 8, 12, 16, etc. Address 14 is obviously in the 12 subnet.
7. D. A point-to-point link uses only two hosts. A /30, or, mask provides two hosts per subnet.
8. C. A /21 is, which means we have a block size of 8 in the third octet, so we just count by 8 until we reach 66. The subnet in this question is 64.0. The next subnet is 72.0, so the broadcast address of the 64 subnet is 71.255.
9. A. A /29 (, regardless of the class of address, has only 3 host bits. Six hosts are the maximum number of hosts on this LAN, including the router interface.
10. C. A /29 is, which is a block size of 8 in the fourth octet. The subnets are 0, 8, 16, 24, 32, 40, etc. is the 24 subnet, and since 32 is the next subnet, the broadcast address for the 24 subnet is 31. is the only correct 
11. A. A /29 ( has a block size of 8 in the fourth octet. This means the subnets are 0, 8, 16, 24, etc. 10 is in the 8 subnet. The next subnet is 16, so 15 is the broadcast address.
12. B. You need 5 subnets, each with at least 16 hosts. The mask provides 16 subnets with 14 hosts—this will not work. The mask provides 8 subnets, each with 30 hosts. This is the best answer.
13. C. First, you cannot answer this question if you can’t subnet. The with a mask of is a block size of 64 in the fourth octet. The host is in the zero subnet, and the error occurred because ip subnet-zero is not enabled on the router.
14. A. A /25 mask is Used with a Class B network, the third and fourth octets are used for subnetting with a total of 9 subnet bits, 8 bits in the third octet and 1 bit in the fourth octet. Since there is only 1 bit in the fourth octet, the bit is either off or on—which is a value of 0 or 128. The host in the question is in the 0 subnet, which has a broadcast address of 127 since 112.128 is the next subnet.
Chapter 5: VLSMs, Summarization, and Troubleshooting TCP/IP 995
15. A. A /28 is a mask. Let’s count to the ninth subnet (we need to find the broadcast address of the eighth subnet, so we need to count to the ninth subnet). Starting at 16 (remember, the question stated that we will not use subnet zero, so we start at 16, not 0), 16, 32, 48, 64, 80, 96, 112, 128, 144 etc.. The eighth subnet is 128 and the next subnet is 144, so our broadcast address of the 128 subnet is 143. This makes the host range 129–142. 142 is the last valid host.
16. C. A /28 is a mask. The first subnet is 16 (remember that the question stated not to use subnet zero) and the next subnet is 32, so our broadcast address is 31. This makes our host range 17–30. 30 is the last valid host.
17. E. A Class C subnet mask of is 3 bits on and 5 bits off (11100000) and provides 8 subnets, each with 30 hosts. However, if the command ip subnet-zero is not used, then only 6 subnets would be available for use.
18. E. A Class B network ID with a /22 mask is, with a block size of 4 in the third octet. The network address in the question is in subnet with a broadcast address of Only option E has the correct subnet mask listed, 
and is a valid host.
19. D,E The router’s IP address on the E0 interface is, which is This makes the third octet a block size of 2. The router’s interface is in the 2.0 subnet, and the broadcast address is 3.255 because the next subnet is 4.0. The 
valid host range is 2.1 through 3.254. The router is using the first valid host address in the range.
20. C. To test the local stack on your host, ping the loopback interface of
Chapter 5: VLSMs, Summarization, and Troubleshooting TCP/IP
1. D. A point-to-point link uses only two hosts. A /30, or, mask provides two hosts per subnet.
2. C. Using a /28 mask, there are 4 bits available for hosts. Two to the fourth power minus 2 = 14.
3. D. For 6 hosts we need to leave 3 bits in the host portion since 2 to the third power = 8 
and 8 less 2 is 6.With 3 bits for the host portion, that leaves 29 bits for the mask or /29.
4. C. To use VLSM, the routing protocols in use possess the capability to transmit subnet mask information.
996 Appendix B u Answers to Review Questions
5. D. In a question like this, you need to look for an interesting octet where you can combine networks. In this example, the third octet has all our subnets so we just need to find our block size now. If we used a block of 8 starting at, then we cover through However, if we used, then we’d cover a block of 16 which would be from through, which is the best answer. 
6. C. The IP address of the station and the gateway are not in the same network. Since the address of the gateway is correct on the station, it is most likely the IP address of the station is incorrect. 
7. B. With an incorrect gateway, Host A will not be able to communicate with the router or beyond the router but will be able to communicate within the subnet.
8. A. Pinging the remote computer would fail if any of the other tests fail. 
9. C. When a ping to the local host IP address fails, you can assume the NIC is not functional.
10. C, D. If a ping to the local host succeeds, you can rule out IP stack or NIC failure.
11. E. A /29 mask yields only 6 addresses, so none of the networks could use it.
12. A. The most likely problem if you can ping a computer by IP address but not by name is a failure of DNS.
13. D. When you issue the ping command, you are using the ICMP protocol.
14. B. The traceroute command displays the networks traversed on a path to a network destination.
15. C. The ping command tests connectivity to another station. The full command is shown below.
Pinging with 32 bytes of data:
Reply from bytes=32 time<1ms TTL=128
Reply from bytes=32 time<1ms TTL=128
Reply from bytes=32 time<1ms TTL=128
Reply from bytes=32 time<1ms TTL=128
Ping statistics for
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 0ms, Maximum = 0ms, Average = 0ms
Chapter 6: Cisco’s Internetworking Operating System (IOS) 997
arp -a
show ip arp
ipconfig /all
Displays the list of routers on a path to a network destination
Displays IP-to-MAC-address mappings on a Windows PC
Displays the ARP table on a Cisco router
Shows you the PC network configuration
The command uses the functions described in the answer table.
17. C. The interesting octet in this example is the second octet, and it is a block size of four starting at By using a mask, we are telling the summary to use a block size of four in the 2nd octet. This will cover through This 
is the best answer. 
18. A. The command that displays the ARP table on a Cisco router is show ip arp.
19. C. The /all switch must be added to the ipconfig command on a PC to verify DNS configuration.
20. C. If you start at and go through, you can see this is a block of 32 in the third octet. Since the network address is always the first one in the range, the summary address is What mask provides a block of 32 in the third octet? The answer is, or /19.
Chapter 6: Cisco’s Internetworking 
Operating System (IOS)
1. D. Typically we’d see the input errors and CRC statistics increase with a duplex error, but it could be another Physical layer issue such as the cable might be receiving excessive interference or the network interface cards might have a failure. Typically you can 
tell if it is interference when the CRC and input errors output grow but the collision counters do not, which is the case with this question. 
2. C. Once the IOS is loaded and up and running, the startup-config will be copied from NVRAM into RAM and from then on, referred to as the running-config.
3. C, D. To configure SSH on your router, you need to set the username command, the ip domain-name, login local, and the transport input ssh under the VTY lines and the crypto key command. However, SSH version 2 is suggested but not required.
4. C. The show controllers serial 0/0 command will show you whether either a DTE or DCE cable is connected to the interface. If it is a DCE connection, you need to add clocking with the clock rate command.
998 Appendix B u Answers to Review Questions
Mode Definition
User EXEC mode Commands that affect the entire system Privileged EXEC mode Commands that affect interfaces/processes only Global configuration mode Interactive configuration dialog Specific configuration modes Provides access to all other router commands Setup mode Limited to basic monitoring commands User exec mode is limited to basic monitoring commands; privileged exec mode provides access to all other router commands. Specific configuration modes include the 
commands that affect a specific interface or process, while global configuration mode allows commands that affect the entire system. Setup mode is where you access the interactive configuration dialog.
6. B. We can see that the bandwidth is 100000 Kbit, which is 100,000,000. Kbit means 
to add three zeros, which is 100 Mbits per second, or FastEthernet.
7. B. From global configuration mode, use the line vty 0 4 command to set all five default 
VTY lines. However, you would typically always set all lines, not just the defaults.
8. C. The enable secret password is case sensitive, so the second option is wrong. To set the enable secret password, use the enable secret password command from global configuration mode. This password is automatically encrypted.
9. C. The typical banner is a message of the day (MOTD) and is set by using the global configuration mode command banner MOTD.
10. C. The prompts offered as options indicate the following modes:
Switch(config)# is global configuration mode.
Switch> is user mode.
Switch# is privileged mode.
Switch(config-if)# is interface configuration mode.
11. D. To copy the running-config to NVRAM so that it will be used if the router is restarted, use the copy running-config startup-config command in privileged 
mode (copy run start for short).
12. D. To allow a VTY (Telnet) session into your router, you must set the VTY password. Option C is wrong because it is setting the password on the wrong router. Notice that you have to set the password before you set the login command. Remember, Cisco may have you set the password before the login command. 
Chapter 7: Managing a Cisco Internetwork 999
13. D. The erase startup-config command erases the contents of NVRAM and will put you in setup mode if the switch is restarted. Option E is wrong because you must type in the full command!
14. B. If an interface is shut down, the show interface command will show the interface as administratively down. (It is possible that no cable is attached, but you can’t tell that from this message.)
15. C. With the show interfaces command, you can view the configurable parameters, get statistics for the interfaces on the switch, check for input and CRC errors, and verify if the interfaces are shut down.
16. C. If you delete the startup-config and reload the switch, the device will automatically enter setup mode. You can also type setup from privileged mode at any time. 
17. D. You can view the interface statistics from user mode, but the command is show interface fastethernet 0/0.
18. B. The % ambiguous command error means that there is more than one possible show command that starts with r. Use a question mark to find the correct command.
19. B, D. The commands show interfaces and show ip interface will show you the layer 1 and 2 status and the IP addresses of your router’s interfaces.
20. A. If you see that a serial interface and the protocol are both down, then you have a Physical layer problem. If you see serial1 is up, line protocol is down, then you are not receiving (Data Link) keepalives from the remote end.
Chapter 7: Managing a Cisco Internetwork
1. B. The IEEE created a new standardized discovery protocol called 802.1AB for Station and Media Access Control Connectivity Discovery. We’ll just call it Link Layer Discovery Protocol (LLDP).
2. C. The show processes (or show processes cpu) is a good tool for determining a given router’s CPU utilization. When it is high, it is not a good time to execute a debug command. 
3. B. The command traceroute (trace for short), which can be issued from user mode or privileged mode, is used to find the path a packet takes through an internetwork and will also show you where the packet stops because of an error on a router.
4. C. Since the configuration looks correct, you probably didn’t screw up the copy job. However, when you perform a copy from a network host to a router, the interfaces are automatically shut down and need to be manually enabled with the no shutdown command.
1000 Appendix B u Answers to Review Questions
5. D. Specifying the address of the DHCP server allows the router to relay broadcast traffic destined for a DHCP server to that server.
6. C. Before you start to configure the router, you should erase the NVRAM with the erase startup-config command and then reload the router using the reload command.
7. C. This command can be run on both routers and switches and it displays detailed information about each device connected to the device you’re running the command on, including the IP address.
8. C. The Port ID column describes the interfaces on the remote device end of the connection.
9. C. This command can be run on both routers and switches, and it displays detailed information about each device connected to the device you’re running the command on, including the IP address.
10. C. If you save a configuration and reload the router and it comes up either in setup mode or as a blank configuration, chances are you have the configuration register setting incorrect.
11. D. To keep open one or more Telnet sessions, use the Ctrl+Shift+6 and then X keystroke combination.
12. B, D. The best answers, the ones you need to remember, are that either an access control list is filtering the Telnet session or the VTY password is not set on the remote device.
13. A, D. The show hosts command provides information on temporary DNS entries and permanent name-to-address mappings created using the ip host command.
14. A, B, D. The tracert command is a Windows command and will not work on a router or switch! IOS uses the traceroute command.
15. D. Since the question never mentioned anything about a suspended session, you can assume that the Telnet session is still open, and you would just type exit to close the session.
16. C. To see console messages through your Telnet session, you must enter the terminal monitor command.
17. terminal monitor When you telnet into a remote device, you will not see console messages by default. For example, you will not see debugging output. To allow console messages to be sent to your Telnet session, use the terminal monitor command.
18. E. Although option A is certainly the “best” answer, unfortunately option E will work just fine and your boss would probably prefer you to use the show cdp neighbors detail command.
Chapter 8: IP Routing 1001
19. D. To enable a device to be an NTP client, use the ntp server IP_address version number command at global configuration mode. That’s all there is to it! Assuming your NTP server is working of course.
20. B, D. You can verify your NTP client with the show ntp status and show ntp associations commands.
Chapter 8: IP Routing
1. show ip route The ip route command is used to display the routing table of a router.
2. B. In the new 15 IOS code, Cisco defines a different route called a local route. Each has a /32 prefix defining a route just for the one address.
3. A, B. Although option D almost seems right, it is not; the mask is the mask used on the remote network, not the source network. Since there is no number at the end of the static route, it is using the default administrative distance of 1.
4. C, F. The switches are not used as either a default gateway or other destination. Switches have nothing to do with routing. It is very important to remember that the destination MAC address will always be the router’s interface. The destination address of a frame, from HostA, will be the MAC address of the Fa0/0 interface of RouterA. The destination address of a packet will be the IP address of the network interface card (NIC) of the HTTPS server. The destination port number in the segment header will have a value of 443 (HTTPS).
5. B. This mapping was learned dynamically which means it was learned through ARP.
6. B. Hybrid protocols use aspects of both distance vector and link state—for example, EIGRP. Although be advised that Cisco typically just calls EIGRP an advanced distance vector routing protocol. Do not be mislead by the way the question is worded. Yes, I know that MAC addresses are not in a packet. You must read the question for understanding of what they are really asking.
7. A. Since the destination MAC address is different at each hop, it must keep changing. The IP address which is used for the routing process does not. 
8. B, E. Classful routing means that all hosts in the internetwork use the same mask and that only default masks are in use. Classless routing means that you can use variable length subnet masks (VLSMs).
9. B, C. The distance-vector routing protocol sends its complete routing table out of all active interfaces at periodic time intervals. Link-state routing protocols send updates containing the state of their own links to all routers in the internetwork.
1002 Appendix B u Answers to Review Questions
10. C. This is how most people see routers, and certainly they could do this type of plain ol’ packet switching in 1990 when Cisco released their very first router and traffic was seriously slow, but not in today’s networks! This process involves looking up every destination in the routing table and finding the exit interface for every packet.
11. A, C. The S* shows that this is a candidate for default route and that it was configured manually. 
12. B. RIP has an administrative distance (AD) of 120, while EIGRP has an administrative distance of 90, so the router will discard any route with a higher AD than 90 to that same network.
13. D. Recovery from a lost route requires manual intervention by a human to replace the 
lost route.
14. A. RIPv1 and RIPv2 only use the lowest hop count to determine the best path to a remote network.
15. A. Since the routing table shows no route to the network, the router will discard the packet and send an ICMP destination unreachable message out of interface FastEthernet 0/0, which is the source LAN from which the packet originated.
16. C. Static routes have an administrative distance of 1 by default. Unless you change this, a static route will always be used over any other dynamically learned route. EIGRP has an administrative distance of 90, and RIP has an administrative distance of 120, by default.
17. C. BGP is the only EGP listed.
18. D. Recovery from a lost route requires manual intervention by a human to replace the lost route. The advantages are less overhead on the router and network, as well as more security.
19. C. The show ip interface brief command displays a concise summary of the interfaces.
20. B. The 150 at the end changes the default administrative distance (AD) of 1 to 150.
Chapter 9: Open Shortest Path First (OSPF)
1. B. Only the EIGRP routes will be placed in the routing table because it has the lowest administrative distance (AD), and that is always used before metrics.
2. A, B, C. Any router that is member of two areas must be an area border router or ABR.
Chapter 9: Open Shortest Path First (OSPF) 1003
3. A, C. The process ID for OSPF on a router is only locally significant and you can use the same number on each router, or each router can have a different number—it just doesn’t matter. The numbers you can use are from 1 to 65,535. Don’t get this confused 
with area numbers, which can be from 0 to 4.2 billion.
4. B. The router ID (RID) is an IP address used to identify the router. It need not and should not match.
5. C. The router ID (RID) is an IP address used to identify the router. Cisco chooses the router ID by using the highest IP address of all configured loopback interfaces. If no loopback interfaces are configured with addresses, OSPF will choose the highest IP address of all active physical interfaces.
6. A. The administrator typed in the wrong wildcard mask configuration. The wildcard should have been or even
7. A. A dash (-) in the State column indicates no DR election, because they are not required on a point-to-point link such as a serial connection. 
8. D. By default the administrative distance of OSPF is 110.
9. A. Hello packets are addressed to multicast address 10. A. The show ip ospf neighbor command displays all interface-related neighbor information. This output shows the DR and BDR (unless your router is the DR or BDR), the RID of all directly connected neighbors and the IP address and name of the directly connected interface.
11. A. is used on broadcast networks to reach the DR and BDR.
12. D. The Hello and Dead timers must be set the same on two routers on the same link or they will not form an adjacency (relationship). The default timers for OSPF are 10 seconds for the Hello timer and 40 seconds for the Dead timer.
13.Designated router contains only the best routes Topological database elected on broadcast networks Hello protocol contains all routes learned Routing table provides dynamic neighbor discovery
A designated router is elected on broadcast networks. Each OSPF router maintains an identical database describing the AS topology. A Hello protocol provides dynamic neighbor discovery. A routing table contains only the best routes.
1004 Appendix B u Answers to Review Questions
14. passive-interface fastEthernet 0/1 The command passive-interface fastEthernet 0/1 will disable OSPF on the specified interface only.
15. B, G. To enable OSPF, you must first start OSPF using a process ID. The number is 
irrelevant; just choose a number from 1 to 65,535 and you’re good to go. After you 
start the OSPF process, you must configure interfaces on which to activate OSPF using the network command with wildcards and specification of an area. Option F is wrong because there must be a space after the parameter area and before you list the area number.
16. A. The default OSPF interface priority is 1, and the highest interface priority determines the designated router (DR) for a subnet. The output indicates that the router with a router ID of is currently the backup designated router (BDR) for the segment, which indicates that another router became the DR. It can be then be assumed that the DR router has an interface priority higher than 2. (The router serving the DR function is not present in the truncated sample output.)
17. A, B, C. OSPF is created in a hierarchical design, not a flat design like RIP. This decreases routing overhead, speeds up convergence, and confines network instability to a single area of the network.
18. show ip ospf interface The show ip ospf interface command displays all interface-related OSPF information. Data is displayed about OSPF information for all OSPF-enabled interfaces or for specified interfaces.
19. A. LSA packets are used to update and maintain the topological database.
20. B. At the moment of OSPF process startup, the highest IP address on any active interface will be the router ID (RID) of the router. If you have a loopback interface configured (logical interface), then that will override the interface IP address and become the RID of the router automatically.
Chapter 10: Layer 2 Switching
1. A. Layer 2 switches and bridges are faster than routers because they don’t take up time looking at the Network Layer header information. They do make use of the Data Link layer information.
2. mac address-table static aaaa.bbbb.cccc vlan 1 int fa0/7 You can set a static MAC address in the MAC address table and when done it will appear as a static entry in the table.
3. B, D, E. Since the MAC address is not present in the table, it will send the frame out of all ports in the same VLAN with the exception of the port on which it was received.
Chapter 10: Layer 2 Switching 1005
4. show mac address-table This command displays the forward filter table, also called a content addressable memory (CAM) table.
5.Address learning
Packet forwarding
Layer three security
Forward/filter decisions
Loop avoidance
Address learning
Forward/filter decisions
Loop avoidance
The three functions are address learning, forward/filter decisions, and loop avoidance.
6. A, D. In the above output, you can see that the port is in Secure-shutdown mode and the light for the port would be amber. To enable the port again you’d need to do the following:
S3(config-if)#no shutdown
7. switchport port-security maximum 2 The maximum setting of 2 means only two MAC addresses can be used on that port; if the user tries to add another host on that segment, the switch port will take the action specified. In the port-security violation command. 
8. B. The switchport port-security command enables port security, which is a prerequisite for the other commands to function.
9. B. Gateway redundancy is not an issue addressed by STP.
10. A. If no loop avoidance schemes are put in place, the switches will flood broadcasts endlessly throughout the internetwork. This is sometimes referred to as a broadcast storm.
11. B, C. Shutdown and protect mode will alert you via SNMP that a violation has occurred on a port.
12. Spanning tree protocol (STP) STP is a switching loop avoidance scheme use by switches.
13. ip default-gateway If you want to manage your switches from outside your LAN, you need to set a default gateway on the switches, just as you would with a host.
14. C. The IP address is configured under a logical interface, called a management domain or VLAN 1.
1006 Appendix B u Answers to Review Questions
15. B. The show port-security interface command displays the current port security and status of a switch port, as in this sample output:
Switch# show port-security interface fastethernet0/1
Port Security: Enabled
Port status: SecureUp
Violation mode: Shutdown
Maximum MAC Addresses: 2
Total MAC Addresses: 2
Configured MAC Addresses: 2
Aging Time: 30 mins
Aging Type: Inactivity
SecureStatic address aging: Enabled
Security Violation count: 0
16. switchport port-security mac-address sticky Issuing the switchport port-security mac-address sticky command will allow a switch to save a dynamically learned MAC address in the running-configuration of the switch, which prevents the administrator from 
having to document or configure specific MAC addresses.
17. B, D. To limit connections to a specific host, you should configure the MAC address of the host as a static entry associated with the port, although be aware that this host can still connect to any other port, but no other port can connect to f0/3, in this example. 
Another solution would be to configure port security to accept traffic only from the MAC address of the host. By default, an unlimited number of MAC addresses can be learned on a single switch port, whether it is configured as an access port or a trunk 
port. Switch ports can be secured by defining one or more specific MAC addresses that should be allowed to connect and by defining violation policies (such as disabling the port) to be enacted if additional hosts try to gain a connection.
18. D. The command statically defines the MAC address of 00c0.35F0.8301 as an allowed host on the switch port. By default, an unlimited number of MAC addresses can be learned on a single switch port, whether it is configured as an access port or a trunk 
port. Switch ports can be secured by defining one or more specific MAC addresses that should be allowed to connect and violation policies (such as disabling the port) if additional hosts try to gain a connection.
19. D. You would not make the port a trunk. In this example, this switchport is a member of one VLAN. However, you can configure port security on a trunk port, but again, not valid for this question.
20. switchport port-security violation shutdown This command is used to set the reaction of the switch to a port violation of shutdown.
Chapter 11: VLANs and InterVLAN Routing 1007
Chapter 11: VLANs and 
InterVLAN Routing
1. D. Here’s a list of ways VLANs simplify network management:
uu Network adds, moves, and changes are achieved with ease by just configuring a 
port into the appropriate VLAN.
uu A group of users that need an unusually high level of security can be put into its 
own VLAN so that users outside of the VLAN can’t communicate with them.
uu As a logical grouping of users by function, VLANs can be considered independent 
from their physical or geographic locations.
uu VLANs greatly enhance network security if implemented correctly.
uu VLANs increase the number of broadcast domains while decreasing their size.
2. ip routing Routing must be enabled on the layer 3 switch.
3. C. VLANs can span across multiple switches by using trunk links, which carry traffic 
for multiple VLANs.
4. B. While in all other cases access ports can be a member of only one VLAN, most switches will allow you to add a second VLAN to an access port on a switch port for your voice traffic; it’s called the voice VLAN. The voice VLAN used to be called the auxiliary VLAN, which allowed it to be overlaid on top of the data VLAN, enabling both types of traffic through the same port.
5. A. Yes, you have to do a no shutdown on the VLAN interface. 
6. C. Unlike ISL which encapsulates the frame with control information, 802.1q inserts an 802.1q field along with tag control information.
7. D. Instead of using a router interface for each VLAN, you can use one FastEthernet interface and run ISL or 802.1q trunking. This allows all VLANs to communicate through one interface. Cisco calls this a “router on a stick.”
8. switchport access vlan 2 This command is executed under the interface (switch port) that is being placed in the VLAN.
9. show vlan After you create the VLANs that you want, you can use the show vlan command to check them out.
10. B. The encapsulation command specifying the VLAN for the subinterface must be present under both subinterfaces.
1008 Appendix B u Answers to Review Questions
11. A. With a multilayer switch, enable IP routing and create one logical interface for each VLAN using the interface vlan number command and you’re now doing inter-VLAN routing on the backplane of the switch!
12. A. Ports Fa0/15–18 are not present in any VLANs. They are trunk ports. 
13. C. Untagged frames are members of the native VLAN, which by default is VLAN 1.
14. sh interfaces fastEthernet 0/15 switchport This show interfaces interface switchport command shows us the administrative mode of dynamic desirable and that the port is a trunk port, DTP was used to negotiate the frame tagging method of ISL, and the native VLAN is the default of 1.
15. C. VLANs are not location dependent and can span to multiple switches using trunk links. Moreover, they can be subnets of major networks.
16. B. The host’s default gateway should be set to the IP address of the subinterface that is associated with the VLAN of which the host is a member, in this case VLAN 2.
17. C. Frame tagging is used when VLAN traffic travels over a trunk link. Trunk links carry frames for multiple VLANs. Therefore, frame tags are used for identification of frames from different VLANs.
18. vlan 2 To configure VLANs on a Cisco Catalyst switch, use the global config vlan command. 
19. B. 802.1q uses the native VLAN.
20. switchport nonegotiate You can use this command only when the interface switchport mode is access or trunk. You must manually configure the neighboring interface as a trunk interface to establish a trunk link.
Chapter 12: Security
1. D. It’s compared with lines of the access list only until a match is made. Once the packet matches the condition on a line of the access list, the packet is acted upon and no further comparisons take place.
2. C. The range of to is a block size of 32. The network 
address is and the mask would be, which for an access 
list must be a wildcard format of The 31 is used for a block size of 32. 
The wildcard is always one less than the block size.
3. C. Using a named access list just replaces the number used when applying the list to the 
router’s interface. ip access-group Blocksales in is correct.
Chapter 12: Security 1009
4. B. The list must specify TCP as the Transport layer protocol and use a correct wild￾card mask (in this case, and it must specify the destination port (80). It also 
should specify all as the set of computers allowed to have this access. 
5. A. The first thing to check in a question like this is the access-list number. Right away, 
you can see that the second option is wrong because it is using a standard IP access-list 
number. The second thing to check is the protocol. If you are filtering by upper-layer 
protocol, then you must be using either UDP or TCP; this eliminates the fourth option. 
The third and last answers have the wrong syntax.
6. C. Of the available choices, only the show ip interface command will tell you which 
interfaces have access lists applied. show access-lists will not show you which interfaces have an access list applied.
show access-list Shows only the parameters for the access list 110.
This command does not show you the interface the list
is set on.
show access-list 110 Shows only the IP access lists configured on the router.
show ip access-list Shows which interfaces have access lists set.
show ip interface Displays all access lists and their parameters configured
on the router. This command does not show you which
interface the list is set on.
The command show access-list displays all access lists and their parameters configured 
on the router; it does not show you which interface the list is set on. show access-list 
110 shows only the parameters for the access list 110 and, again, does not tell you which 
interface the list is set on. show ip access-list reveals only the IP access lists configured 
on the router. Finally, show ip interface shows which interfaces have access lists set.
The functions of each command are as shown in the solution graphic.
8. C. The extended access list ranges are 100–199 and 2000–2699, so the access-list 
number of 100 is valid. Telnet uses TCP, so the protocol TCP is valid. Now you just 
need to look for the source and destination address. Only the third option has the cor￾rect sequence of parameters. Option B may work, but the question specifically states 
“only” to network, and the wildcard in option B is too broad.
9. D. Extended IP access lists use numbers 100–199 and 2000–2699 and filter based on 
source and destination IP address, protocol number, and port number. The last option 
is correct because of the second line that specifies permit ip any any. (I used, which is the same as the any option.) The third option does not have 
this, so it would deny access but not allow everything else.
1010 Appendix B u Answers to Review Questions
10. D. First, you must know that a /20 is, which is a block size of 16 in 
the third octet. Counting by 16s, this makes our subnet 48 in the third octet, and the 
wildcard for the third octet would be 15 since the wildcard is always one less than the 
block size.
11. B. To find the wildcard (inverse) version of this mask, the zero and one bits are simply 
reversed as follows:
11111111.11111111.11111111.11100000 (27 one bits, or /27)
00000000.00000000.00000000.00011111 (wildcard/inverse mask)
12. A. First, you must know that a /19 is, which is a block size of 32 in the 
third octet. Counting by 32s, this makes our subnet 192 in the third octet, and the 
wildcard for the third octet would be 31 since the wildcard is always one less than the 
block size.
13. B. The scope of an access list is determined by the wildcard mask and the network 
address to which it is applied. For example, in this case the starting point of the 
list of addresses affected by the mask is the network ID The wild￾card mask is Adding the value of the last octet in the mask to the network 
address (32 + 31 = 63) tells you where the effects of the access list ends, which is Therefore, all addresses in the range– 
will be denied by this list.
14. C. To place an access list on an interface, use the ip access-group command in interface configuration mode.
15. B. With no permit statement, the ACL will deny all traffic.
16. D. If you add an access list to an interface and you do not have at least one permit statement, then you will affectively shut down the interface because of the implicit deny any 
at the end of every list.
17. C. Telnet access to the router is restricted by using either a standard or extended IP access list inbound on the VTY lines of the router. The command access-class is used to apply the access list to the VTY lines.
18. C. A Cisco router has rules regarding the placement of access lists on a router interface. You can place one access list per direction for each layer 3 protocol configured on an interface.
19. C. The most common attack on a network today is a denial of service (DoS) because they are the easiest attack to achieve.
20. C. Implementing intrusion detection services and intrusion prevention services will help notify you and stop attacks in real time. 
Chapter 13: Network Address Translation 1011
Chapter 13: Network Address Translation
1. A, C, E. NAT is not perfect and can cause some issues in some networks, but most networks work just fine. NAT can cause delays and troubleshooting problems, and some applications just won’t work.
2. B, D, F. NAT is not perfect, but there are some advantages. It conserves global addresses, which allow us to add millions of hosts to the Internet without “real” IP addresses. This provides flexibility in our corporate networks. NAT can also allow you to use the same subnet more than once in the same network without overlapping networks.
3. C. The command debug ip nat will show you in real time the translations occurring on your router.
4. A. The command show ip nat translations will show you the translation table containing all the active NAT entries.
5. D. The command clear ip nat translations * will clear all the active NAT entries in your translation table.
6. B. The show ip nat statistics command displays a summary of the NAT configuration as well as counts of active translation types, hits to an existing mapping, misses 
(causing an attempt to create a mapping), and expired translations.
7. B. The command ip nat pool name creates the pool that hosts can use to get onto the 
global Internet. What makes option B correct is that the range through includes 30 hosts, but the mask has to match 30 hosts as well, and that 
mask is Option C is wrong because there is a lowercase t 
in the pool name. Pool names are case sensitive.
8. A, C, E. You can configure NAT three ways on a Cisco router: static, dynamic, and 
NAT Overload (PAT).
9. B. Instead of the net-mask command, you can use the prefix-length length statement.
10. C. In order for NAT to provide translation services, you must have ip nat inside and 
ip nat outside configured on your router’s interfaces.
11. A, B, D. The most popular use of NAT is if you want to connect to the Internet and 
you don’t want hosts to have global (real) IP addresses, but options B and D are correct 
as well.
12. C. An inside global address is considered to be the IP address of the host on the private 
network after translation.
1012 Appendix B u Answers to Review Questions
13. A. An inside local address is considered to be the IP address of the host on the private 
network before translation.
14. D. What we need to figure out for this question is only the inside global pool. Basically 
we start at and end at; our block size is 8 in the third octet, or 
/21. Always look for your block size and the interesting octet and you can find your 
answer every time.
15. B. Once you create your pool, the command ip nat inside source must be used to 
say which inside locals are allowed to use the pool. In this question we need to see if 
access-list 100 is configured correctly, if at all, so show access-list is the best answer.
16. A. You must configure your interfaces before NAT will provide any translations. On the 
inside network interfaces, you would use the command ip nat inside. On the outside 
network interfaces, you will use the command ip nat outside.
17. B. You must configure your interfaces before NAT will provide any translations. On 
the inside networks you would use the command ip nat inside. On the outside network interfaces, you will use the command ip nat outside.
18. C. Another term for Port Address Translation is NAT Overload because that is the keyword 
used to enable port address translation.
19. B. Fast-switching is used on Cisco routers to create a type of route cache in order to 
quickly forward packets through a router without having to parse the routing table for 
every packet. As packets are processed-switched (looked up in the routing table), this 
information is stored in the cache for later use if needed for faster routing processing.
20. B. Once you create a pool for the inside locals to use to get out to the global Internet, 
you must configure the command to allow them access to the pool. The ip nat inside 
source list number pool-name overload command has the correct sequence for this 
Chapter 14: Internet Protocol 
Version 6 (IPv6)
1. B. Unlike unicast addresses, global unicast addresses are meant to be routed.
2. A. Packets addressed to a unicast address are delivered to a single interface. For load 
balancing, multiple interfaces can use the same address.
3. C. Link-local addresses are meant for throwing together a temporary LAN for meetings or a small LAN that is not going to be routed but needs to share and access files 
and services locally.
Chapter 14: Internet Protocol Version 6 (IPv6) 1013
4. D. These addresses are meant for non-routing purposes like link-local, but they are 
almost globally unique, so it is unlikely they will have an address overlap. Unique local 
addresses were designed as a replacement for site-local addresses.
5. B. Packets addressed to a multicast address are delivered to all interfaces identified with 
the multicast address, the same as in IPv4. It is also called a one-to-many address. You 
can always tell a multicast address in IPv6 because multicast addresses always start 
with FF.
6. C. Anycast addresses identify multiple interfaces, which is somewhat similar to multicast 
addresses; however, the big difference is that the any-cast packet is only delivered to one 
address, the first one it finds defined in the terms of routing distance. This address can 
also be called one-to-one-of-many, or one-to-nearest.
7. C. The loopback address with IPv4 is With IPv6, that address is ::1.
8. C, D. Adjacencies and next-hop attributes now use link-local addresses, and OSPFv3 
still uses multicast traffic to send its updates and acknowledgments with the addresses 
FF02::5 for OSPF routers and FF02::6 for OSPF designated routers. These are the 
replacements for and, respectively.
9. A, C. Host A would send an RS to R1, which would respond with an RA, if the host 
hasn’t already learned this information previously. The host now has the default gate￾way information it needs to send packets to a remote network. IPv6, like IPv4, has 
both a network portion and host portion in the IPv6 packet.
10. C. A router solicitation is sent out using the all-routers multicast address of FF02::2. 
The router can send a router advertisement to all hosts using the FF02::1 multicast 
11. B. This can be a hard question if you don’t remember to invert the 7th bit! Always 
look for the 7th bit when studying for the Cisco exams. The EUI-64 autoconfiguration inserts an FF:FE in the middle of the 48-bit MAC address to create a unique IPv6 
12. A. The NDP neighbor advertisement (NA) contains the MAC address. A neighbor 
solicitation (NS) was initially sent asking for the MAC address.
13. A. To enable OSPFv3, you enable the protocol at the interface level as with RIPng. The 
command string is ipv6 ospf process-id area area-id.
14. B, D. To shorten the written length of an IPv6 address, successive fields of zeros may be 
replaced by double colons. In trying to shorten the address further, leading zeros may 
also be removed. Just as with IPv4, a single device’s interface can have more than one 
address; with IPv6 there are more types of addresses and the same rule applies. There 
can be link-local, global unicast, multicast, and anycast addresses all assigned to the 
same interface.
1014 Appendix B u Answers to Review Questions
15. C, D. IPv4 addresses are 32 bits long and are represented in decimal format. IPv6 
addresses are 128 bits long and represented in hexadecimal format.
16. B. There are no broadcasts with IPv6. Unicast, multicast, anycast, global, and link local unicast are used.
17. D. There are 16 bits (four hex characters) in an IPv6 field.
18. A, D. Global addresses start with 2000::/3, link-locals start with FE80::/10, loopback 
is ::1, and unspecified is just two colons (::). Each interface will have a loopback address 
automatically configured.
19. B, C. If you verify your IP configuration on your host, you’ll see that you have multiple IPv6 addresses, including a loopback address. The last 64 bits represent the 
dynamically created interface ID, and leading zeros are not mandatory in a 16-bit 
IPv6 field.
20. C, D, E. OSPFv2 does not use the network command under global configuration mode, 
nor does it use wildcard masks as IPv4 does. However, they can both use the interface 
command to configure OSPF, use a 32-bit RID, and both use LSAs.
Chapter 15: Enhanced Switched 
1. B, D. The switch is not the root bridge for VLAN 1 or the output would tell us exactly 
that. We can see that the root bridge for VLAN 1 is off of interface G1/2 with a cost of 
4, meaning it is directly connected. Use the command show cdp nei to find your root 
bridge at this point. Also, the switch is running RSTP (802.1d), not STP.
2. D. If you have a server or other devices connected into your switch that you’re totally 
sure won’t create a switching loop if STP is disabled, you can use something called 
PortFast on these ports. Using it means the port won’t spend the usual 50 seconds to 
come up while STP is converging. Understand this doesn’t completely disable STP, just 
stops any port configured with PortFast from transitioning the different port states, 
and immediately puts the port into forwarding state.
3. A, D. It is important that you can find your root bridge, and the show spanning-tree
command will help you do this. To quickly find out which VLANs your switch is the 
root bridge for, use the show spanning-tree summary command.
4. A. 802.1w is the also called Rapid Spanning Tree Protocol. It is not enabled by default 
on Cisco switches, but it is a better STP to run because it has all the fixes that the Cisco 
extensions provide with 802.1d. Remember, Cisco runs RSTP PVST+, not just RSTP.
Chapter 15: Enhanced Switched Technologies 1015
5. B. The Spanning Tree Protocol is used to stop switching loops in a layer 2 switched 
network with redundant paths.
6. C. Convergence occurs when all ports on bridges and switches have transitioned to 
either the forwarding or blocking states. No data is forwarded until convergence is 
complete. Before data can be forwarded again, all devices must be updated.
7. C, E. There are two types of EtherChannel: Cisco’s PAgP and the IEEE’s LACP. They 
are basically the same, and there is little difference to configuring them. For PAgP, 
use auto or desirable mode, and with LACP use passive or active. These modes decide 
which method you are using, and they must be configured the same on both sides of 
the EtherChannel bundle.
8. A, B, F. RSTP helps with convergence issues that plague traditional STP. Rapid PVST+ 
is based on the 802.1w standard in the same way that PVST+ is based on 802.1d. The 
operation of Rapid PVST+ is simply a separate instance of 802.1w for each VLAN.
9. D. BPDU Guard is used when a port is configured for PortFast, or it should be used, 
because if that port receives a BPDU from another switch, BPDU Guard will shut that 
port down to stop a loop from occurring.
10. C. To allow for the PVST+ to operate, there’s a field inserted into the BPDU to accommodate the extended system ID so that PVST+ can have a root bridge configured on 
a per-STP instance. The extended system ID (VLAN ID) is a 12-bit field, and we can 
even see what this field is carrying via the show spanning-tree command output.
11. C. PortFast and BPDU Guard allow a port to transition to the forwarding state quickly, 
which is great for a switch port but not for load balancing. You can somewhat load balance with RSTP, but that is out of the scope of our objectives, and although you can use 
PPP to configure multilink (bundle links), this is performed on asynchronous or synchronous serial links. Cisco’s EtherChannel can bundle up to eight ports between switches.
12. D. If the Spanning Tree Protocol is not running on your switches and you connect them 
together with redundant links, you will have broadcast storms and multiple frame copies; 
you will have broadcast storms and multiple frame copies being received by the same 
destination device..
13. B, C, E. All the ports on both sides of every link must be configured exactly the same 
or it will not work. Speed, duplex, and allowed VLANs must match.
14. D, F. There are two types of EtherChannel: Cisco’s PAgP and the IEEE’s LACP. They 
are basically the same, and there is little difference to configure them. For PAgP, use the 
auto or desirable mode, and with LACP use the passive or active mode. These modes 
decide which method you are using, and they must be configured the same on both sides 
of the EtherChannel bundle.
15. D. You can’t answer this question if you don’t know who the root bridge is. SC has 
a bridge priority of 4,096, so that is the root bridge. The cost for SB was 4, with the 
1016 Appendix B u Answers to Review Questions
direct link, but that link went down. If SB goes through SA to SC, the cost would be 
4 + 19, or 23. If SB goes to SA to SD to SC, the cost is 4 + 4 + 4 = 12.
16. A, D. To configure EtherChannel, create the port channel from global configuration 
mode, and then assign the group number on each interface using the active mode to 
enable LACP, although just configuring the channel-group command under your interfaces will enable the bundle, but options A and D are the best Cisco objective answers.
17. A, D. You can set the priority to any value from 0 through 61,440 in increments of 
4,096. Setting it to zero (0) means that the switch will always be a root as long as it has 
a lower MAC than another switch with its bridge ID also set to 0. You can also force a 
switch to be a root for a VLAN with the spanning-tree vlan vlan primary command. 
18. A. By using per-VLAN spanning tree, the root bridge can be placed in the center 
of where all the resources are for a particular VLAN, which enables optimal path 
19. A, C, D, E. Each 802.1d port transitions through blocking, listening, learning, and 
finally forwarding after 50 seconds, by default. RSTP uses discarding, learning, 
and forwarding only.
20. A, C, D, E, F. The roles a switch port can play in STP are root, non-root, designated, 
non-designated, forwarding, and blocking. Discarding is used in RSTP, and disabled 
could be a role, but it’s not listed as a possible answer.
Chapter 16: Managing Cisco Devices
1. B. The default configuration setting is 0x2102, which tells the router to load the IOS 
from flash and the configuration from NVRAM. 0x2142 tells the router to bypass the 
configuration in NVRAM so that you can perform password recovery.
2. E. To copy the IOS to a backup host, which is stored in flash memory by default, use 
the copy flash tftp command.
3. B. To install a new license on an ISR G2 router, use the license install url command.
4. C. The configuration register provides the boot commands, and 0x2101 tells the router to 
boot the mini-IOS, if found, and not to load a file from flash memory. Many newer rout￾ers do not have a mini-IOS, so as an alternative, the router would end up in ROM monitor 
mode if the mini-IOS is not found. However, option C is the best answer for this question. 
5. B. The show flash command will provide you with the current IOS name and size and 
the size of flash memory.
6. C. Before you start to configure the router, you should erase the NVRAM with the erase 
startup-config command and then reload the router using the reload command.
Chapter 16: Managing Cisco Devices 1017
7. D. The command copy tftp flash will allow you to copy a new IOS into flash memory 
on your router.
8. C. The best answer is show version, which shows you the IOS file running currently 
on your router. The show flash command shows you the contents of flash memory, not 
which file is running.
9. C. All Cisco routers have a default configuration register setting of 0x2102, which tells 
the router to load the IOS from flash memory and the configuration from NVRAM.
10. C. If you save a configuration and reload the router and it comes up either in setup 
mode or as a blank configuration, chances are the configuration register setting is 
11. D. The License boot module command installs a Right-To-Use license feature on 
a router.
12. A. The show license command determines the licenses that are active on your system. 
It also displays a group of lines for each feature in the currently running IOS image 
along with several status variables related to software activation and licensing, both 
licensed and unlicensed features.
13. B. The show license feature command allows you to view the technology package 
licenses and feature licenses that are supported on your router along with several status vari￾ables related to software activation and licensing, both licensed and unlicensed features.
14. C. The show license udi command displays the unique device identifier (UDI) of the 
router, which comprises the product ID (PID) and serial number of the router.
15. D. The show version command displays various information about the current IOS 
version, including the licensing details at the end of the command’s output.
16. C. The license save flash command allows you to back up your license to 
flash memory.
17. C. The show version command provides you with the current configuration 
register setting.
18. C, D. The two steps to remove a license are to first disable the technology package and 
then clear the license.
19. B, D, E. Before you back up an IOS image to a laptop directly connected to a router’s 
Ethernet port, make sure that the TFTP server software is running on your laptop, that 
the Ethernet cable is a “crossover,” and that the laptop is in the same subnet as the router’s 
Ethernet port, and then you can use the copy flash tftp command from your laptop.
20. C. The default configuration setting of 0x2102 tells the router to look in NVRAM for 
the boot sequence.
1018 Appendix B u Answers to Review Questions
Chapter 17: IP Services
1. B. You can create and then enter the ACL into the snmp-server command when setting 
your SNMP configuration on a router.
2. C. GLBP is a Cisco proprietary FHRP that can provide true load-balancing. Instead of 
having active and passive routers, all routers on a LAN can be forwarders with GLBP.
3. C. The default priority is 100, and if you change the priority to a higher setting, you 
provide the router with a better chance of being active, but only if the FHRP configured 
routers come up at the same time. 
4. A. The command service sequence-numbers adds a sequence number to each system 
5. C. With NetFlow, you can collect information about the flow of traffic on the network, 
including address and protocols in use. A recent version of NetFlow is version 9, referred 
to as Flexible NetFlow.
6. F. There are eight different trap levels. If you choose level 4, level 0 through 4 will be 
displayed, giving you emergency, alert, critical, and error messages as well as warning 
messages. Here are the levels and what they perform. 
Router (config) #logging trap ?
Logging severity level
Immediate action needed
Critical conditions
Debugging messages
System is unusable
Error conditions
Informational messages
Normal but significant conditions
Warning conditions
7. C. HSRP can keep track of outside interfaces to switch routers from passive to active if 
the WAN on one router goes down, for example.
8. B. The show ip cache flow command provide a summary of the NetFlow statistics, 
including which protocols are in use.
9. B, C, D. NetFlow, SNMP, and syslog are all different applications that provide dif￾ferent features for administrating your network. NetFlow is a very powerful Cisco 
tool that allows you to see who is doing what, understand network capacity, and even 
gather accounting information.
Chapter 17: IP Services 1019
10. D. There are eight different trap levels. If you choose level 5, level 0 through 5 will be 
displayed, giving you emergency, alert, critical, error, and warning messages as well as 
notification messages. Here are the levels and what they perform.
Router (config) #logging trap ?
Logging severity level
Immediate action needed
Critical conditions
Debugging messages
System is unusable
Error conditions
Informational messages
Normal but significant conditions
Warning conditions
11. B, C. There is a logging host command configured to, so all messages will 
be sent there, but don’t forget that all messages are always sent to the memory buffers 
on a router as well. Debugging is trap level 7.
12. B, D. You need to have a Cisco router to run the proprietary NetFlow application, plus 
you need a server to send the information to, and this is called a collector.
13. B. There are eight different trap levels. If you choose level 3, level 0 through 3 will be 
displayed, giving you emergency, alert, and critical messages as well as error messages. 
Here are the levels and what they perform.
Router (config) #logging trap ?
Logging severity level
Immediate action needed
Critical conditions
Debugging messages
System is unusable
Error conditions
Informational messages
Normal but significant conditions
Warning conditions
14. C. The active virtual router (AVR) responds with the virtual MAC addresses to the clients.
15. B. With HSRP, the command is show standby; with GLBP it is simply show glbp, or 
even show glbp brief.
1020 Appendix B u Answers to Review Questions
16. C. There are eight different trap levels. If you choose level 7, level 0 through 7 will be 
displayed, giving you emergency, alert, critical, error, warning, notification, and informa￾tional messages as well as debugging messages. Here are the levels and what they perform.
Router (config) #logging trap ?
Logging severity level
Immediate action needed
Critical conditions
Debugging messages
System is unusable
Error conditions
Informational messages
Normal but significant conditions
Warning conditions
17. C. HSRP is not true load balancing, but it does provide more than one active router in 
only one situation; that is, if you have your router interface connected to a trunk link 
and then configured with subinterfaces, no different than router on a stick. However, 
only one router can be active for a LAN, unlike with GLBP.
18. G. There are eight different trap levels. If you choose level 6, level 0 through 6 will be 
displayed, giving you emergency, alert, critical, error, warning, and notification messages 
as well as informational messages. Here are the levels and what they perform.
Router (config) #logging trap ?
Logging severity level
Immediate action needed
Critical conditions
Debugging messages
System is unusable
Error conditions
Informational messages
Normal but significant conditions
Warning conditions
19. C. SNMPv3 supports strong authentication with MD5 or SHA, providing confidentiality (encryption) and data integrity of messages via DES or DES-256 encryption between 
agents and managers. 
20. C, D. Both HSRP and GLBP are Cisco proprietary FHRPs, but only GLBP can load-balance between multiple routers on the same LAN.
Chapter 18: Troubleshooting IP, IPv6, and VLANs 1021
Chapter 18: Troubleshooting IP, IPv6, 
and VLANs
1. D. Positive confirmation has been received confirming that the path to the neighbor is 
functioning correctly. REACH is good!
2. B. The most common cause of interface errors is a mismatched duplex mode between 
two ends of an Ethernet link. If they have mismatched duplex settings, you’ll receive a 
legion of errors, which cause nasty slow performance issues, intermittent connectivity, 
and massive collisions—even total loss of communication!
3. D. You can verify the DTP status of an interface with the sh dtp interface interface
4. A. No DTP frames are generated from the interface. Nonegotiate can be used only if 
the neighbor interface is manually set as trunk or access. 
5. D. The command show ipv6 neighbors provides the ARP cache on a router.
6. B. The state is STALE when the interface has not communicated within the neighbor 
reachable time frame. The next time the neighbor communicates, the state will change 
back to REACH.
7. B. There is no IPv6 default gateway, which will be the link-local address of the 
router interface, sent to the host as a router advertisement. Until this host receives 
the router address, the host will communicate with IPv6 only on the local subnet. 
8. D. This host is using IPv4 to communicate on the network, and without an IPv6 global 
address, the host will be able to communicate to only remote networks with IPv4. The 
IPv4 address and default gateway are not configured into the same subnet.
9. B, C. The commands show interface trunk and show interface interface switchport will show you statistics of ports, which includes native VLAN information.
10. A. Most Cisco switches ship with a default port mode of auto, meaning that they will 
automatically trunk if they connect to a port that is on or desirable. Remember that 
not all switches are shipped as mode auto, but many are, and you need to set one side 
to either on or desirable in order to trunk between switches. 
1022 Appendix B u Answers to Review Questions
Chapter 19: Enhanced IGRP
1. B. Only the EIGRP routes will be placed in the routing table because it has the lowest 
administrative distance (AD), and that is always used before metrics.
2. A, C. EIGRP maintains three tables in RAM: neighbor, topology, and routing. The neighbor and topology tables are built and maintained with the use of Hello and update packets.
3. B. EIGRP does use reported distance, or advertised distance (AD), to tell neighbor 
routers the cost to get to a remote network. This router will send the FD to the neighbor router and the neighbor router will add the cost to get to this router plus the AD 
to find the true FD.
4. E. Successor routes are going to be in the routing table since they are the best path to a 
remote network. However, the topology table has a link to each and every network, so the 
best answer is topology table and routing table. Any secondary route to a remote network 
is considered a feasible successor, and those routes are found only in the topology table 
and used as backup routes in case of primary route failure.
5. C. Any secondary route to a remote network is considered a feasible successor, and 
those routes are found only in the topology table and used as backup routes in case 
of primary route failure. You can see the topology table with the show ip eigrp 
topology command.
6. B, C, E. EIGRP and EIGRPv6 routers can use the same RID, unlike OSPF, and this 
can be set with the eigrp router-id command. Also a variance can be set to provide 
unequal-cost load balancing, along with the maximum-paths command to set the amount 
of load-balanced paths.
7. C. There were two successor routes, so by default, EIGRP was load-balancing out s0/0 
and s0/1. When s0/0 goes down, EIGRP will just keep forwarding traffic out the second 
link s0/1. s0/0 will be removed from the routing table. 
8. D. To enable EIGRPv6 on a router interface, use the command ipv6 eigrp as on 
individual interfaces that will be part of the EIGRPv6 process.
9. C. The path to network out serial0/0 is more than two times the current FD, so 
I used a variance 3 command to load-balance unequal-cost links three times the FD. 
10. B, C. First, a maximum hop count of 16 only is associated with RIP, and EIGRP never 
broadcasts, so we can eliminate A and D as options. Feasible successors are backup 
routes and stored in the topology table, so that is correct, and if no feasible successor is 
located, the EIGRP will flood its neighbors asking for a new path to network
11. D. The show ip eigrp neighbors command allows you to check the IP addresses as 
well as the re-transmit interval and queue counts for the neighbors that have established 
an adjacency.
Chapter 19: Enhanced IGRP 1023
12. C, E. For EIGRP to form an adjacency with a neighbor, the AS numbers must match, 
and the metric K-values must match as well. Also, option F could cause the problem; 
we can see if it is causing a problem from the output given.
13. A, D. Successor routes are the routes picked from the topology table as the best route 
to a remote network, so these are the routes that IP uses in the routing table to forward 
traffic to a remote destination. The topology table contains any route that is not as good 
as the successor route and is considered a feasible successor, or backup route. Remember 
that all routes are in the topology table, even successor routes.
14. A, B. Option A will work because the router will change the network statement to since EIGRP uses classful addresses by default. Therefore, it isn’t technically a wrong answer, but please understand why it is correct for this question. The subnet address can be configured with wildcards just as we use with 
OSPF and ACLs. The /27 is a block of 32, so the wildcard in the fourth octet will be 31. 
The wildcard of is wrong because this is a network address, not a host address, 
and the is wrong because that is only a block of 16 and would only work if the 
mask was a /28.
15. C. To troubleshoot adjacencies, you need to check the AS numbers, the K-values, 
networks, passive interfaces, and ACLs.
16. C. EIGRP and EIGRPv6 will load-balance across 4 equal cost-paths by default but can 
be configured to load-balance across equal- and unequal-cost paths, up to 32 with IOS 
15.0 code.
17. B, E. EIGRP must be enabled with an AS number from global configuration mode 
with the ipv6 router eigrp as command if you need to set the RID or other global 
parameters. Instead of configuring EIGRP with the network command as with EIGRP, 
EIGRPv6 is configured on a per-interface basis with the ipv6 eigrp as command.
18. C. There isn’t a lot to go on from with the output, but that might make this easier than 
if there were a whole page of output. Since s0/0/2 has lowest FD and AD, that would 
become the successor route. For a route to become a feasible successor, its reported distance must be lower than the feasible distance of the current successor route, so C 
is our best answer based on what we can see.
19. C. The network in the diagram is considered a discontiguous network because you have 
one classful address sub-netted and separated by another classful address. Only RIPv2, 
OSPF, and EIGRP can work with discontiguous networks, but RIPv2 and EIGRP won’t 
work by default (except for routers running the new 15.0 code). You must use the no 
auto-summary command under the routing protocol configuration. There is a passive 
interface on RouterB, but this is not on an interface between RouterA and RouterB and 
won’t stop an adjacency. 
1024 Appendix B u Answers to Review Questions
20. A, B, C, D. Here are the documented steps that Cisco says to check when you have an 
adjacency issue:
uu Interfaces between the devices are down.
uu The two routers have mismatching EIGRP autonomous system numbers.
uu Proper interfaces are not enabled for the EIGRP process.
uu An interface is configured as passive.
uu K values are mismatched.
uu EIGRP authentication is misconfigured.
Chapter 20: Multi-Area OSPF
1. A, B, D. As the size of a single-area OSPF network grows, so does the size of the routing 
table and OSPF database that have to be maintained. Also, if there is a change in network 
topology, the OSPF algorithm has to be rerun for the entire network.
2. B. An autonomous system boundary router (ASBR) is any OSPF router that is connected 
to an external routing process (another AS). An ABR, on the other hand, connects one 
(or more) OSPF areas together to area 0.
3. B, D, E. In order for two OSPF routers to create an adjacency, the hello and dead timers must match, and they must both be configured into the same area as well as being 
in the same subnet. Also, if authentication is configured, that info must match as well.
4. C. The process starts by sending out Hello packets. Every listening router will then add 
the originating router to the neighbor database. The responding routers will reply with 
all of their Hello information so that the originating router can add them to its own 
neighbor table. At this point, we will have reached the 2WAY state—only certain routers 
will advance beyond this to establish adjacencies.
5. D. If you have multiple links to the same network, you can change the default cost of a 
link so OSPF will prefer that link over another with the ip ospf cost cost command.
6. B. In the FULL state, all LSA information is synchronized among adjacent neighbors. 
OSPF routing can begin only after the FULL state has been reached. The FULL state 
occurs after the LOADING state finishes.
7. B, D, E. Configuring OSPFv3 is pretty simple, as long as you know what interfaces you 
are using on your router. There are no network statements, OSPFv3 is configured on a 
per-interface basis. OSPFv2 and OSPFv3 both use a 32-bit RID, have an IPv4 address 
configured on at least one interface, you do not need to manually set a RID when configuring EIGRPv3.
Chapter 20: Multi-Area OSPF 1025
8. A. Cisco uses a simple calculation of 108/bandwidth of a link to determine the cost. 
This means anything that is 100 Mbps or higher will have a default cost of 1.
9. B. Referred to as a network link advertisement (NLA), Type 2 LSAs are generated by 
designated routers (DRs). Remember that a designated router is elected to represent 
other routers in its network, and it establishes adjacencies with them. The DR uses a 
Type 2 LSA to send out information about the state of other routers that are part of 
the same network.
10. C. Referred to as summary link advertisements (SLAs), Type 3 LSAs are generated by 
area border routers. These ABRs send Type 3 LSAs toward the area external to the 
one where they were generated. The Type 3 LSA advertises networks, and these LSAs 
advertise inter-area routes to the backbone area (area 0).
11. D. To see all LSAs a router has learned from its neighbors, you need to see the OSPF 
LSDB, and you can see this with the show ip ospf database command.
12. B. Based on the information in the question, the cost from R1 to R2 is 4, the cost from 
R2 to R3 is 15, and the cost from R3 to R5 is 4. 15 + 4 + 4 = 23. Pretty simple.
13. B, D. Since R3 is connected to area 1 and R1 is connected to area 2 and area 0, the 
routes advertised from R3 would show as OI, or inter-area routes.
14. A, D, E, F. For two OSPF routers to form an adjacency, they must be in the same area, 
must be in the same subnet, and must have authentication information match, if configured. You need to also check if an ACL is set and if a passive interface is configured.
15. C. The IOS command show ip ospf neighbor shows neighbor router information, 
such as neighbor ID and the state of adjacency with the neighboring router.
16. D. The command show ip ospf interface on a default broadcast multi-access network 
will show you DRs and BDRs on that network.
17. A, C, D, F. It’s hard to tell from this single output what is causing the problem with 
the adjacency, but we need to check the ACL 10 to see what that is doing, verify 
that the routers are in the same area and in the same subnet, and see if that passive 
interface is configured with the interface we’re using.
18. B, D, G. The default reference bandwidth is 100 by default, and you can change it 
under the OSPF process with the auto-cost reference bandwidth number command, 
but if you do, you need to configure this command on all routers in your AS.
19. A, D. Anything Fast Ethernet or above would have a default cost of 1, and serial interfaces 
have a default cost of 64.
20. D. Anything Fast Ethernet or above would have a default cost of 1, and serial interfaces 
have a default cost of 64. 
1026 Appendix B u Answers to Review Questions
Chapter 21: Wide Area Networks
1. C. The command debug ppp authentication will show you the authentication process 
that PPP uses across point-to-point connections.
2. B. If you have a router in your Frame Relay network that does not support IARP, 
you must create Frame Relay maps on your router, which provide known DLCI-to IP-address mappings.
3. C. The key is “there are no free ports” on your router. Only Frame Relay can provide a 
connection to multiple locations with one interface, and in an economical manner no less.
4. C, D, E. The show frame-relay ? command provides many options, but the options 
available in this question are lmi, pvc, and map.
5. A. If you have a serial port configured with multiple DLCIs connected to multiple remote 
sites, split horizon rules (discussed in Chapter 5) stop route updates received on an interface from being sent out the same interface. By creating subinterfaces for each PVC, you 
can avoid the split horizon issues when using Frame Relay. 
6. C, D, E. Ethernet and Token Ring are LAN technologies and cannot be configured on 
a serial interface. PPP, HDLC, and Frame Relay are layer 2 WAN technologies that are 
typically configured on a serial interface.
7. C. It is very important to remember when studying the CCNA R/S exam objectives, 
and when configuring Frame Relay with point-to-point subinterfaces, that you do not 
put an IP address on the physical interface. 
8. A. Clocking on a serial interface is always provided by the CSU/DSU (DCE device). 
However, if you do not have a CSU/DSU in your non-production test environment, then 
you need to supply clocking with the clock rate command on the serial interface of 
the router with the DCE cable attached.
9. C. Frame Relay, by default, is a non-broadcast multi-access (NBMA) network, which 
means that broadcasts, such as RIP updates, will not be forwarded across the link 
by default.
10. C. PPPoE encapsulates PPP frames in Ethernet frames and uses common PPP features 
like authentication, encryption, and compression. PPPoA is used for ATM.
11. C. If you have a Cisco router on one side of a Frame Relay network and a non-Cisco 
router on the other side, you would need to use the Frame Relay encapsulation type of 
IETF. The default is Cisco encapsulation, which means that a Cisco router must be on 
both sides of the Frame Relay PVC.
12. C. The show interfaces command shows the configuration settings and the interface 
status as well as the IP address and tunnel source and destination address.
Chapter 21: Wide Area Networks 1027
13. B, C, D. This is just a basic WAN question to test your understanding of connections. 
PPP does not need to be used, so option A is not valid. You can use any type of connection to connect to a customer site, so option B is a valid answer. You can also use any 
type of connection to get to the Frame Relay switch, as long as the ISP supports it, and 
T1 is valid, so option C is okay. Ethernet as a WAN can be used with Ethernet over 
MPLS (EoMPLS); however, you don’t need to configure a DLCI unless you’re using 
Frame Relay, so E is not a valid answer for this question.
14. B. All web browsers support Secure Sockets Layer (SSL), and SSL VPNs are known as 
Web VPNs. Remote users can use their browser to create an encrypted connection and 
they don’t need to install any software. GRE doesn’t encrypt the data.
15. E. This is an easy question because the Remote router is using the default HDLC serial 
encapsulation and the Corp router is using the PPP serial encapsulation. You should go to 
the Remote router and set that encapsulation to PPP or change the Corp router back to the 
default of HDLC by typing no encapsulation under the interface.
16. A, C, E. VPNs can provide very good security by using advanced encryption and 
authentication protocols, which will help protect your network from unauthorized 
access. By connecting the corporate remote offices to their closest Internet provider 
and then creating a VPN tunnel with encryption and authentication, you’ll gain a huge 
savings over opting for traditional leased point-to-point lines. VPNs scale very well to 
quickly bring up new offices or have mobile users connect securely while traveling or 
when connecting from home. VPNs are very compatible with broadband technologies.
17. C. Even though the IP addresses don’t look correct, they are in the same subnet, so 
option B is not correct. The question states that you can ping the other side, so the PVC 
must be up— option A can’t be correct. You cannot configure IARP, so only option C 

can be correct. Since a Frame Relay network is a non-broadcast multi-access network 

by default, broadcasts such as RIP updates cannot be sent across the PVC unless you 
use the broadcast statement at the end of the frame-relay map command.
18. D. IP-sec is an industry-wide standard suite of protocols and algorithms that allows for 
secure data transmission over an IP-based network that functions at the layer 3 Network 
layer of the OSI model.
19. C. A VPN allows or describes the creation of private networks across the Internet, 
enabling privacy and tunneling of TCP/IP protocols. A VPN can be set up across any 
type of link.
20. B. As I mentioned many times in this chapter, and you need to remember this, DLCIs 
are locally significant only and define the circuit from the router to the switch only. 
They do not reference a remote router or DLCI. Lab_A would use DLCI 100 to get to 

the Lab_B networks. RouterB would use DLCI 200 to get to the Lab_A networks.


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