200-301

Number: 200-301

Passing Score: 800

Time Limit: 120 min

File Version: 1

200-301

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Exam A

QUESTION 1

You are the network administrator for your company and have configured Cisco Discovery Protocol (CDP) in your network. You recently noticed that when devices send large numbers of CDP neighbor announcements, some devices are crashing. You decide to disable CDP on the router.

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Which command should you use to achieve the objective?

A.no cdp run

B.set cdp disable

C.no cdp enable

D.no cdp advertise-v2

Correct Answer: A

Section: (none)

Explanation

Explanation/Reference:

Explanation:

You should use the no cdp run command to disable CDP on the router. Due to a known vulnerability regarding the handling of CDP by Cisco routers and switches when devices send large numbers of CDP neighbor announcements, some devices can crash or cause abnormal system behavior. To overcome this problem, you can disable CDP for the entire router by using the no cdp run command.

You cannot use the set cdp disable command to disable CDP on the router. This command disables CDP on an entire Catalyst switch. You cannot use the no cdp enable command to disable CDP on the router. This command disables CDP on a specific interface.

You cannot use the no cdp advertise-v2 command to disable CDP on the router. This command disables CDPv2 advertisements.

Objective:

LAN Switching Fundamentals

Sub-Objective:

Configure and verify Layer 2 protocols

References:

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Cisco > Support > Using Cisco Discovery Protocol

Cisco > Support > Technology Support > Network Management > Cisco’s Response to the CDP Issue > Document ID: 13621

QUESTION 2

Which is NOT a valid range for private IP addresses?

A.10.0.0.0 — 10.255.255.255

B.172.16.0.0 — 172.31.255.255

C.192.168.0.0 — 192.168.255.255

D.192.255.255.255-193.0.0.0

Correct Answer: D

Section: (none)

Explanation

Explanation/Reference:

Explanation:

The range 192.255.255.255 — 193.0.0.0 is a valid public IP address range, not a private IP address range.

The Internet Assigned Numbers Authority (IANA) has reserved the following three ranges for private Internet use:

10.0.0.0— 10.255.255.255 (10.0.0.0/8)

172.16.0.0— 172.31.255.255 (172.16.0.0/12) 192.168.0.0 — 192.168.255.255 (192.168.0.0/16)

The Internet Assigned Numbers Authority (IANA) manages and distributes global public IP addresses. IANA also performs DNS root zone management. IANA operates with the help of International Engineering Task Force (IETF) and RFC Editor to manage IP address allocation and DNS root zone management. There are Regional Internet Registries (RIRs) through which IANA allocates local registrations of IP addresses to different regions of the world. Each RIR handles a specific region of the world.

Objective:

Network Fundamentals

Sub-Objective:

Describe the need for private IPv4 addressing

References:

http://www.ietf.org/rfc/rfc1918.txt

http://www.iana.org/

QUESTION 3

Which of the following protocols allow the root switch location to be optimized per VLAN? (Choose all that apply.)

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A.PVST+

B.RSTP

C.PVRST

D.STP

Correct Answer: AC

Section: (none)

Explanation

Explanation/Reference:

Explanation:

Both Per VLAN Spanning Tree Plus (PVST+) and Per VLAN Rapid Spanning Tree (PVRST) protocols allow for a spanning tree instance for each VLAN, allowing for the location optimization of the root bridge for each VLAN. These are Cisco proprietary enhancements to the 802.1d and 802.1w standards, respectively.

Rapid Spanning Tree Protocol (RSTP) is another name for the 802.1w standard. It supports only one instance of spanning tree.

Spanning Tree Protocol (STP) is another name for the 802.1d standard. It supports only one instance of spanning tree.

Objective:

LAN Switching Fundamentals

Sub-Objective:

Configure, verify, and troubleshoot STP protocols

References:

Cisco Home > Support > Technology Support > LAN Switching

QUESTION 4

Your assistant just finished configuring a small test network as part of his training. The network is configured as shown in the diagram below:

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When testing the configuration, you find that Host A in the diagram cannot ping Host B.

Which of the following pairs of connections are required to be in the same subnet for Host A to be able to ping Host B? (Choose all that apply.)

A.The IP address of Host A and the IP address of the Fa0/0 interface of Router A

B.The IP address of the Fa0/0 interface of Router A and the IP address of the Fa0/0 interface of Router B

C.The IP address of Host A and the IP address of the Fa0/0 interface of Router B

D.The IP address of Host A and the IP address of Switch A

E.The IP address of the S 0/0 interface of Router A and the IP address of the S 0/0 interface of Router B

F.The IP address of Host A and the IP address of Host B

G.The IP address of Host B and the IP address of the Fa0/0 interface of Router B

Correct Answer: AEG

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Section: (none)

Explanation

Explanation/Reference:

Explanation:

The following pairs of connections are required to be in the same subnet:

the IP address of Host A and the IP address of the Fa0/0 interface of Router A

the IP address of the S 0/0 interface of Router A and the IP address of the S 0/0 interface of Router B the IP address of Host B and the IP address of the Fa0/0 interface of Router B

When troubleshooting a correctly labeled network diagram for IP addressing problems, one must start on one end and trace each link in one direction, ensuring at each step that the interfaces are in the same subnet. A switch simply passes the packet to the router; therefore, the IP address of the switch is not important. It performs its job even if it has no IP address.

Moving from Host A to Host B, however, the following links must be in the same subnet:

The IP address of Host A and the IP address of the Fa0/0 interface of Router A

The IP address of the S0/0 interface of Router A and the IP address of the S0/0 interface of Router B

The IP address of Host B and the IP address of the Fa0/0 interface of Router B

Neither of the switch addresses is important to the process.

If all other routing issues are correct, it is also not required for Host A and Host B to be in the same subnet.

Objective:

Network Fundamentals

Sub-Objective:

Configure, verify, and troubleshoot IPv4 addressing and subnetting

References:

Cisco > Home > Support > Technology Support > IP > IP Routing > Design > Design Technotes > IP Addressing and Subnetting for New Users

QUESTION 5

When a packet is forwarded through a network from one host to another host, which of the following fields in the Ethernet frame will change at every hop?

A.Source IP address

B.Destination MAC address

C.Source port number

D.Destination IP address

Correct Answer: B

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Section: (none)

Explanation

Explanation/Reference:

Explanation:

When an Ethernet frame is forwarded through the network, both the source and destination MAC addresses will change at every hop.

The source and destination IP addresses and source and destination port numbers MUST remain the same for proper routing to occur, for the proper delivery to the destination service, and for the proper reception of responses to the sending device. By contrast, the MAC addresses used at each hop must be those of the physical interfaces involved in the Layer 2 forwarding at each hop.

As a simple illustration of this process, IP addresses and MAC addresses are assigned to two computers and three routers shown in the diagram. The network is arranged as shown below:

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The IP addresses and the MAC addresses of each device are shown below:

There will be four handoffs to get this packet from WKS1 to WKS2. The following table shows the destination IP addresses and destination MAC addresses used at each handoff.

As you can see, the destination IP address in the packet does not change, but the MAC address in the frame changes at each handoff.

Objective:

LAN Switching Fundamentals

Sub-Objective:

Interpret Ethernet frame format

References:

MAC address changes for every new network

QUESTION 6

Which Cisco IOS Cisco Discovery Protocol (CDP) command displays the IP address of the directly connected Cisco devices?

A.show cdp

B.show cdp devices

C.show cdp traffic

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D. show cdp neighbors detail

Correct Answer: D

Section: (none)

Explanation

Explanation/Reference:

Explanation:

The show cdp neighbors detail command displays the IP address of the directly connected Cisco devices. CDP is a Layer 2 (Data Link layer) protocol that finds information about neighboring network devices. CDP does not use Network layer protocols to transmit information because it operates at the Data Link layer. For this reason, IP addresses need not even be configured on the interfaces for CDP to function. The only requirement is that the interfaces be enabled with the no shutdown command. An example of the output of the show cdp neighbors detail command is as follows:

The show cdp devices command is incorrect because this is not a valid Cisco IOS command.

The show cdp command is incorrect because this command is used to view the global CDP information. It lists the default update and holdtime timers, as in the following sample output:

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Atlanta# show cdp

Global CDP information:

Sending CDP packets every 60 seconds

Sending a holdtime value of 180 seconds

Sending CDPv2 advertisements is enabled

The show cdp traffic command is incorrect because this command displays traffic information between network devices collected by the CDP, as in the following example:

Birmingham# show cdp traffic

Total packets output: 652, Input: 214

Hdr syntax: 0, Chksum error: 0, Encaps failed: 0

No memory: 0, Invalid: 0, Fragmented: 0

CDP version 1 advertisements output: 269, Input: 50

CDP version 2 advertisements output: 360, Input: 25

Objective:

Infrastructure Management

Sub-Objective:

Use Cisco IOS tools to troubleshoot and resolve problems

References:

Cisco > Cisco IOS Network Management Command Reference > schema through show event manager session cli username > show cdp neighbors detail

QUESTION 7

Your assistant is interested in gathering statistics about connection-oriented operations.

Which of the following should be done to enhance the accuracy of the information gathered?

A.configure an IP SLA responder on the destination device

B.configure an IP SLA responder on the source device

C.schedule the operation on the destination device

D.add the verify-data command to the configuration of the operation

Correct Answer: A

Section: (none)

Explanation

Explanation/Reference:

Explanation:

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Any IP SLA operations accuracy can be enhanced by configure an IP SLA responder on the destination device. It is important to note that only Cisco devices support the configuration as a responder.

You do not configure an IP SLA responder on the source device. You schedule the operation on the source device and the destination device is the one that is configured as a responder.

You do not schedule the operation on the destination device. You schedule the operation on the source device and the destination device is the one that is configured as a responder.

Adding the verify-data command to the configuration of the operation will not enhance the accuracy of the information gathered. When data verification is enabled, each operation response is checked for corruption. Use the verify-data command with caution during normal operations because it generates unnecessary overhead.

Objective:

Infrastructure Management

Sub-Objective:

Troubleshoot network connectivity issues using ICMP echo-based IP SLA

References:

IP SLAs Configuration Guide, Cisco IOS Release 15M > Configuring IP SLAs TCP Connect Operations

QUESTION 8

You are the network administrator for your company. You have installed a new router in your network. You want to establish a remote connection from your computer to the new router so it can be configured. You are not concerned about security during the remote connection.

Which Cisco IOS command should you use to accomplish the task?

A.ssh

B.telnet

C.terminal

D.virtual

Correct Answer: B

Section: (none)

Explanation

Explanation/Reference:

Explanation:

The telnet command should be used to establish a remote connection from your computer to the router. The syntax of the command is as follows:

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telnet {{hostname | IP_address mask interface_name} | {IPv6_address interface_name} | {timeoutnumber}}

The following parameters are used with the telnet command: hostname: Specifies the name of the host.

interface_name: Specifies the name of the network interface to which you need to telnet.

IP_address: Specifies the IP address of the host.

IPv6_address: Specifies the IPv6 address associated to the host.

timeout number: Specifies the number of minutes that a telnet session can be idle.

The following features are the key characteristics of Telnet:

It is a client server protocol.

It uses TCP port number 23.

It is used to establish a remote connection over the internet or Local Area Network (LAN).

Telnet does not encrypt any data sent over the connection; that is, the data travels in clear text.

A Cisco router supports five simultaneous telnet sessions, by default. These lines are called vty 0-4.

A successful Telnet connection requires that the destination device be configured to support Telnet connections, which means it must be configured with a Telnet password.

The telnet command can also be used to test application layer connectivity to a device.

The ssh command is incorrect because this command is used to remotely establish a secure connection between two computers over the network.

The terminal command is incorrect because this command is used to change console terminal settings.

The virtual command is incorrect because this command is used along with the http and telnet parameters to configure a virtual server.

Objective:

Infrastructure Management

Sub-Objective:

Configure and verify device management

References:

Cisco > Cisco IOS Terminal Services Command Reference > telnet

QUESTION 9

You are configuring a WAN connection between two offices. You cannot ping between the routers in a test. The Serial0 interface on RouterA is connected to the Serial1 interface on RouterB.

The commands you have executed are shown below. What is the problem with the configuration?

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A.The passwords are incorrectly configured

B.The usernames are incorrectly configured

C.The wrong interface has been configured

D.The encapsulation is incorrect on RouterA

E.The encapsulation is incorrect on RouterB

F.The authentication types do not match

Correct Answer: C

Section: (none)

Explanation

Explanation/Reference:

Explanation:

The two routers are connected using Serial0 on RouterA and Serial1 on RouterB. However, the configuration commands were executed on interface Serial0 on RouterB. So although the configuration itself is completely correct, it is configured on the wrong interface.

The passwords are correct. The passwords should match on both routers. In this case, they are both set to lie. If even one character does not match, including character casing, the authentication and the connection will fail.

The usernames are correct. The username should be set to the host name of the peer router. In this case, RouterA’s username is set to RouterB and RouterB’s username is set to RouterA, which is correct.

The encapsulations are correct. They are both set to PPP, which is the correct type of encapsulation when using authentication.

The authentication types do match. They are both set to CHAP. It is possible to configure two authentication methods, with the second used as a fallback method in cases where the other router does not support the first type. The command below would be used to enable CHAP with PAP as a fallback method:

RouterB(config-if)#ppp authentication chap pap

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Objective:

WAN Technologies

Sub-Objective:

Configure and verify PPP and MLPPP on WAN interfaces using local authentication

References:

Cisco > Home > Support > Technology Support > WAN > Point-To-Point Protocol (PPP) > Design > Design Technotes > Understanding and Configuring PPP CHAP Authentication

QUESTION 10

Which Cisco 2950 switch command or set of commands would be used to create a Virtual LAN (VLAN) named MARKETING with a VLAN number of 25?

A.switch(config)# vtp domain MARKETING 25

B.switch(config)# vlan 25 switch(config-vlan)# name MARKETING

C.switch(config-if)# vlan 25 name MARKETING

D.switch(config)# vtp 25 switch(config-vtp)# name MARKETING

Correct Answer: B

Section: (none)

Explanation

Explanation/Reference:

Explanation:

The following commands would create a VLAN named MARKETING with a VLAN number of 25: switch(config)# vlan 25

switch(config-vlan)# name MARKETING

The steps to add anew VLAN are as follows:

1.Create the new VLAN

2.Name the VLAN

3.Add the desired ports to the VLAN

VLANs on current Cisco switches are configured in global configuration mode. The VLAN is first created with the vlan # command, and then optionally named with the name vlan-name command. Interfaces are added to VLANs using either the interface or interface range commands.

The switch(config)# vtp domain MARKETING 25 command will not create a VLAN. This command creates a VLAN Trunking Protocol (VTP) domain. VTP is a means of synchronizing VLANs between switches, not a method of manually creating VLANs.

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The vlan 25 name command is deprecated, and is not supported on newer Cisco switches. Even on switches that support the command, this answer is incorrect because the vlan 25 name command was issued in VLAN database mode, rather than interface mode.

Objective:

LAN Switching Fundamentals

Sub-Objective:

Configure, verify, and troubleshoot VLANs (normal/extended range) spanning multiple switches

References:

Cisco > Support > LAN Switching > Virtual LANS / VLAN Trunking Protocol (VLANS/VTP) > Configure > Configuration Examples and Technotes > Configuring VLAN Trunk Protocol (VTP) > Document ID: 98154

QUESTION 11

What command would be used to verify trusted DHCP ports?

A.show mls qos

B.show ip dhcp snooping

C.show ip trust

D.show ip arp trust

Correct Answer: B

Section: (none)

Explanation

Explanation/Reference:

Explanation:

The command show ip dhcp snooping is used to verify trusted DHCP ports. This command is used to verify which ports are intended to have DHCP servers connected to them.

DHCP snooping creates an IP address to MAC address database that is used by Dynamic ARP Inspection (DAI) to validate ARP packets. It compares the MAC address and IP address in ARP packets, and only permits the traffic if the addresses match. This eliminates attackers that are spoofing MAC addresses.

DHCP snooping is used to define ports as trusted for DHCP server connections. The purpose of DHCP snooping is to mitigate DHCP spoofing attacks. DHCP snooping can be used to determine what ports are able to send DHCP server packets, such as DHCPOFFER, DHCPACK, and DHCPNAK. DHCP snooping can also cache the MAC address to IP address mapping for clients receiving DHCP addresses from a valid DHCP server.

MLS QOS has no bearing on DHCP services, so show mls qos is not correct.

The other commands are incorrect because they have invalid syntax.

Objective:

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Infrastructure Security

Sub-Objective:

Describe common access layer threat mitigation techniques

References:

Cisco > Cisco IOS IP Addressing Services Command Reference > DHCP Commands > show ip dhcp snooping

QUESTION 12

R1 and R2 are connected as shown in the diagram and are configured as shown in output in the partial output of the show run command.

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The command ping R2 fails when executed from R1. What command(s) would allow R1 to ping R2 by name?

A.R1(config)#int S1

R1(config-if)#no ip address 192.168.5.5 R1(config-if)# ip address 192.168.5.9 255.255.255.252

B.R1(config)#no ip host R1

R1(config)# ip host R2 192.168.5.6 255.255.255.252

C.R1(config)#no hostname R2 R1(config)# hostname R1

D.R2(config)#int S1

R1(config-if)#no ip address 192.168.5.5 R1(config-if)# ip address 192.168.5.9 255.255.255.0

Correct Answer: B

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Section: (none)

Explanation

Explanation/Reference:

Explanation:

Both routers have been configured with the ip host command. This command creates a name to IP address mapping, thereby enabling the pinging of the device by address. On R1, the mapping is incorrect and needs to be corrected. Currently it is configured as ip host R1 192.168.5.6. It is currently mapping its own name to the IP address of R2.

To fix the problem, you should remove the incorrect IP address mapping and create the correct mapping for R2, as follows:

R1(config)#no ip host R1

R1(config)# ip host R2 192.168.5.6 255.255.255.252

Once this is done, the ping on R2 will succeed.

The IP address of the S1 interface on R1 does not need to be changed to 192.168.5.9 /30. In fact, if that is done the S1 interface on R1 and the S1 interface in R2 will no longer be in the same network. With a 30-bit mask configured, the network they are currently in extends from 192.168.5.4 — 192.168.5.7. They are currently set to the two usable addresses in that network, 192.168.5.5 and 192.168.5.6.

The hostnames of the two routers do need to be set correctly using the hostname command for the ping to function, but they are correct now and do not need to be changed.

The subnet mask of the S1 interface on R2 does not need to be changed to 255.255.255.0. The mask needs to match that of R1, which is 255.255.255.252.

Objective:

Infrastructure Services

Sub-Objective:

Troubleshoot client connectivity issues involving DNS

References:

Cisco IOS IP Command Reference, Volume 1 of 4: Addressing and Services, Release 12.3>IP Addressing and Services Commands: idle through ip local-proxy- arp>ip host

QUESTION 13

You network team is exploring the use of switch stacking.

Which of the following statements is NOT true of switch stacking?

A.The master switch is the only switch with full access to the interconnect bandwidth

B.Switches are connected with special cable

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C.The stack has a single IP address

D.Up to nine switches can be added to the stack

Correct Answer: A

Section: (none)

Explanation

Explanation/Reference:

Explanation:

All switches in the stack have full access to the interconnect bandwidth, not just the master switch. The master switch is elected from one of the stack members. It automatically configures the stack with the currently running IOS image and a single configuration file.

The switches are connected with special cables that form a bidirectional closed loop path.

The stack has a single management IP address and is managed as a unit.

Up to nine switches can be in a stack.

Objective:

LAN Switching Fundamentals

Sub-Objective:

Describe the benefits of switch stacking and chassis aggregation

References:

Products & Services > Switches > Campus LAN Switches — Access > Cisco Catalyst 3750 Series Switches > Data Sheets and Literature > White Papers > Cisco StackWise and StackWise Plus Technology

QUESTION 14

RouterA and RouterB, which connect two locations, are unable to communicate. You run the show running-configuration command on both router interfaces, RouterA and RouterB. The following is a partial output:

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Based on the information given in the output, what are two likely causes of the problem? (Choose two.)

A.The IP address defined is incorrect.

B.Both routers cannot have a clock rate defined.

C.Both routers cannot have an identical clock rate.

D.The Layer 2 framing is misconfigured.

E.At least one of the routers must have the ip mroute-cache command enabled.

Correct Answer: AB

Section: (none)

Explanation

Explanation/Reference:

Explanation:

Two possible causes of the problem are that the IP addresses are incorrect as defined, or that both routers have a defined clock rate. The IP addresses on the routers are in different subnets. The IP addresses need to be changed to fall in the same subnet.

Both routers cannot have a clock rate configured. Only routers with a DCE cable connected should have a clock rate, which provides synchronization to the router connected to the DTE cable. In a point-to-point serial connection, the DCE cable connects to the DTE cable, providing a communication path between the two routers. If both computers have a clock rate configured, the routers will not communicate.

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A matching clock rate is not the problem. The clock rates between two routers should match. The router connected to the DCE cable will provide the clock rate to the router connected to the DTE cable, resulting in matching clock rates.

The Layer 2 encapsulation refers to the Data Link protocol used on the link. In this case, the protocol is Point to Point Protocol (PPP), which is configured correctly on both ends as indicated by the matching encapsulation ppp statements in the output. The connection would be prevented from working if one of the routers were missing this setting (which would be indicated by the absence of the encapsulation ppp statement in its output), or if a different Layer 2 encapsulation type were configured, such as High-Level Data Link Control (HDLC).

The ip mroute-cache command is used to fast-switch multicast packets and would not cause the problem in this scenario.

Objective:

Network Fundamentals

Sub-Objective:

Configure, verify, and troubleshoot IPv4 addressing and subnetting

References:

Cisco > Internetworking Technology Handbook > Point to Point Protocol (PPP)

Cisco > Support > Product Support > Cisco IOS Software Releases 11.1 > Configure > Feature Guides > Clock Rate Command Enhancements Feature Module > clock rate

QUESTION 15

Which of the following commands will set the line speed of a serial connection that connects to a Channel Service Unit /Digital Service Unit (CSU/DSU) at 56 Kbps?

A.service-module 56000 clock rate speed

B.service-module 56k clock rate speed

C.bandwidth 56k

D.bandwidth 56000

Correct Answer: B

Section: (none)

Explanation

Explanation/Reference:

Explanation:

The command service-module 56k clock rate speed will configure the network line speed for a 4-wire,56/64-kbps CSU/DSU module.

The command service-module 56000 clock rate speed is incorrect because the speed must be stated in the form 56k (for Kbps), rather than 56000.

The bandwidth command is used to limit the amount of bandwidth used by an application when utilizing Quality of Service (QOS). It does not set the line speed of a serial connection that connects to a Channel Service Unit /Digital Service Unit CSU/DSU. Therefore, both the bandwidth 56k and the bandwidth 56000 commands are incorrect.

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Objective:

WAN Technologies

Sub-Objective:

Describe WAN access connectivity options

References:

Cisco IOS Interface and Hardware Component Configuration Guide, Release 12.4T > Part 2: Serial Interfaces > Configuring Serial Interfaces > 2-Wire and 4-Wire,56/64-kbps CSU/DSU Service Module Configuration Task List > Setting the Network Line Speed

QUESTION 16

You are discovering that there are differences between the configuration of EIGRP for IPv6 and EIGRP for IPv4. Which statement is true with regard to the difference?

A.A router ID is required for both versions

B.A router ID must be configured under the routing process for EIGRP for IPv4

C.AS numbers are not required in EIGRP for IPv6

D.AS numbers are not required in EIGRP for IPv4

Correct Answer: A

Section: (none)

Explanation

Explanation/Reference:

Explanation:

Both versions of EIGRP require a router ID. The difference is that with EIGRP for IPv6, you must configure a router ID under the routing process if there are no IPv4 addresses on the router. In EIGRP for IPv4, the router can select one of the configured IPv4 addresses as the router ID.

A router ID can be configured under the routing process for EIGRP for IPv4, but it is not required. In EIGRP for IPv4, the router can select one of the configured Pv4 addresses as the router ID.

AS numbers are required in both versions of EIGRP.

Objective:

Routing Fundamentals Sub-Objective:

Configure, verify, and troubleshoot EIGRP for IPv6 (excluding authentication, filtering, manual summarization, redistribution, stub)

References:

Home > Articles > Cisco Certification > CCNA Routing and Switching > C > Cisco ICND2 Foundation Learning Guide: Implementing an EIGRP Solution > Implementing EIGRP for IPv6

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QUESTION 17

Which of the following techniques is NOT used by distance vector protocols to stop routing loops in a network?

A.Split horizon

B.Spanning Tree Protocol (STP)

C.Holddowns

D.Route poisoning

Correct Answer: B

Section: (none)

Explanation

Explanation/Reference:

Explanation:

Spanning Tree Protocol (STP) is not used by distance vector protocols to stop routing loops in a network. STP is used to prevent switching loops in a switched network.

Routing loops can occur due to slow convergence and inconsistent routing tables, and can cause excessive use of bandwidth or complete network failure. An example of a routing table problem would be incorrectly configured static default routes. Suppose that Router A is connected to Router B, and the addresses of the interfaces on each end of the link connecting the two routers are as follows:

Router A 192.168.5.1/24

Router B 192.168.5.2/24

A partial output of the routing tables of the two routers is shown below. Router B hosts the connection to the Internet.

routerA# show ip route

Gateway of last resort is 192.168.5.2 to network 0.0.0.0 <Output omitted>

routerB# show ip route

Gateway of last resort is 192.168.5.1 to network 0.0.0.0 <<output omitted>>

From the limited information shown above, you can see that Router A is pointing to Router B for the default route, and Router B is pointing to Router A for the default route. This will cause a routing loop for any traffic that is not in their routing tables. For example, if a ping were initiated to the address 103.5.6.8 and that address was not in the routing tables of Routers A and B, the most likely message received back would NOT be «destination unreachable» but «TTL expired in transit.» This would be caused by the packet looping between the two routers until the TTL expired.

The following techniques are used by distance vector protocols to stop routing loops in a network:

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Split horizon stops routing loops by preventing route update information from being sent back over the same interface on which it arrived.

Holddown timers prevent regular update messages from reinstating a route that is unstable. The holddown timer places the route in a suspended, or «possibly down» state in the routing table and regular update messages regarding this route will be ignored until the timer expires.

Route poisoning «poisons» a failed route by increasing its cost to infinity (16 hops, if using RIP). Route poisoning is combined with triggered updates to ensure fast convergence in the event of a network change.

Objective:

Routing Fundamentals

Sub-Objective:

Compare and contrast distance vector and link-state routing protocols

References:

Cisco > Articles > Network Technology > General Networking > Dynamic Routing Protocols

QUESTION 18

What command should you use to quickly view the HSRP state of the switch for all HSRP groups of which the switch is a member?

A.switch# show standby brief

B.switch# show ip interface brief

C.switch# show hsrp

D.switch# show standby

Correct Answer: A

Section: (none)

Explanation

Explanation/Reference:

Explanation:

The command show standby brief should be used to quickly view the HSRP state of a switch for all HSRP groups of which it is a member. The summary information it provides includes the group number, priority, state, active device address, standby address, and group address.

The command show standby can be used to display detailed information about HSRP groups of which a switch is a member. This command would not provide a quick view. This command displays information about HSRP on all configured interfaces and for all HSRP groups. It also displays hello timer information and the expiration timer for the standby switch.

The command show ip interface brief is useful in that lists the interfaces and displays the basic IP configuration of each. This output would include the IP address of the interface and the state of the interface, but not HSRP information.

The command show hsrp is not a valid command due to incorrect syntax.

Objective:

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Infrastructure Services

Sub-Objective:

Configure, verify, and troubleshoot basic HSRP

References:

Cisco > Cisco IOS IP Application Services Command Reference > show standby

Cisco > Cisco IOS IP Application Services Configuration Guide, Release 12.4 > Part 1: First Hop Redundancy Protocols > Configuring HSRP

QUESTION 19

When packets are transmitted from one host to another across a routed segment, which two addresses are changed? (Choose two.)

A.source IP address

B.source MAC address

C.destination IP address

D.destination MAC address

Correct Answer: BD

Section: (none)

Explanation

Explanation/Reference:

Explanation:

When packets move from one LAN segment to another LAN segment across a router, the source and destination Media Access Control (MAC) addresses in the packet change.

Packets destined for a remote network must be forwarded by a router that is typically the sending host’s default gateway. The IP address of the remote host is inserted into the packet, while the MAC address of the default gateway is inserted as the Layer 2 address. This ensures that the packet is received by the default gateway. The router then examines the destination IP address, performs a route lookup, and forwards the packet toward the destination, inserting its MAC address as the source MAC address. If the next hop is another router, then the destination MAC address is replaced with the next router’s MAC address. This process is repeated by each router along the path (inserting its own MAC address as the source MAC address and inserting the MAC address of the next router interface as the destination MAC address) until the packet is received by the remote host’s default gateway. The destination gateway then replaces the destination MAC address with the host’s MAC address and forwards the packet.

In the diagram below, when the host located at the IP address 10.0.1.3 sends data to the host located at IP address 10.1.1.3, the Layer 2 and Layer 3 destination addresses will be bb.bb.bb.bb.bb.bb and 10.1.1.3, respectively. Note that the Layer 2 destination address matches the host’s default gateway and not the address of the switch or the destination host.

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It is incorrect to state that the source IP address or the destination IP address change when packets transfer from one host to another across a routed segment. The Internet Protocol (IP) addresses within the packets do not change because this information is needed to route the packet, including any data returned to the sender.

Data return to the sending host is critically dependent on the destination having a default gateway configured and its router having a route back to the sender. If either is missing or configured incorrectly, a return is not possible. For example, when managing a switch remotely with Telnet, the switch cannot be located on the other side of a router from the host being used to connect if the switch does not have a gateway configured. In this case, there will no possibility of a connection being made because the switch will not have a return path to the router.

Objective:

Routing Fundamentals

Sub-Objective:

Describe the routing concepts

References:

Cisco Documentation > Internetworking Technology Handbook > Routing Basics

QUESTION 20

You are connecting a new computer to Switch55. The new computer should be placed in the Accounting VLAN. You execute the show vlan command and get the following output:

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