100-150 Practice Questions

Question 1

What is the broadcast address for the network 172.16.20.0/24?

Accepted Answer

172.16.20.255. In a /24 subnet (255.255.255.0), the network occupies the first three octets, and the last octet is available for hosts. The broadcast address is the very last address in the subnet range, where all host bits are set to one. For the 172.16.20.0 network, the last address is 172.16.20.255. This calculation is essential for identifying network boundaries and verifying traffic scope in Cisco configurations.

Answer

172.16.20.0

Answer

172.16.20.1

Answer

172.16.20.254

Question 2

A network administrator is troubleshooting a switch that is experiencing high CPU utilization. The administrator suspects a switching loop. Which command should be used to verify whether Spanning Tree Protocol has blocked any ports to prevent a loop?

Accepted Answer

show spanning-tree. Spanning Tree Protocol prevents loops by blocking redundant ports. When a loop is suspected, checking STP status is essential. The show spanning-tree command provides detailed information about port roles and states, including which ports are blocking. If STP is functioning correctly, it will have blocked ports to break the loop, though high CPU may still occur during topology changes.

Answer

show interfaces status

Answer

show running-config

Answer

show mac address-table

Question 3

Which protocol is used to provide dynamic, automatic configuration of VLANs across a domain of switches?

Accepted Answer

VTP. VLAN Trunking Protocol (VTP) enables a centralized management of VLAN configurations across a switched network. By creating, deleting, or modifying VLANs on a server switch, those changes are propagated automatically to all client switches in the domain. Understanding VTP is essential for minimizing configuration errors and maintaining consistent VLAN databases in large-scale environments, though modern networks often prefer manual management for improved security control.

Answer

STP

Answer

CDP

Answer

OSPF

Question 4

A technician is examining a frame captured on a switch port and sees the destination MAC address field set to FF:FF:FF:FF:FF:FF. What is the purpose of this address in an Ethernet network?

Accepted Answer

It is a broadcast address that is delivered to all devices on the local network segment.. The all-FF MAC address is the Ethernet broadcast address. When a frame uses it as the destination, all devices in the same broadcast domain receive and process the frame. This is essential for address resolution and dynamic configuration protocols where the sender does not yet know the unicast MAC address of the intended recipient.

Answer

It is a loopback address that causes the frame to be sent back to the originating device.

Answer

It is a multicast address used to send frames to a specific group of devices that have joined a multicast group.

Answer

It is a special address that identifies the default gateway for the local subnet.

Question 5

A small office wants to reduce the risk of malware arriving through email and malicious websites while keeping administration simple. Which two measures provide the strongest protection against these threats? (Choose two.)

Accepted Answer

Install and regularly update endpoint antivirus and anti-malware software on all workstations.. The strongest pairing couples host-level defense with network-level filtering. Endpoint antivirus catches payloads that reach the workstation, while a secure web gateway or DNS filtering service blocks the malicious domains that deliver those payloads. Together they cover both the email and web vectors named in the scenario without heavy administrative overhead, whereas disabling updates, permitting all outbound traffic, and sharing administrator accounts all increase exposure.

Answer

Share a single administrator account among all staff so everyone can fix problems quickly.

Answer

Disable automatic operating system updates to prevent unexpected reboots.

Answer

Allow all outbound traffic from the internal network to simplify troubleshooting.

Question 6

Users on VLAN 20 report that they can reach servers on VLAN 30 but cannot reach any hosts on VLAN 40. The administrator confirms that inter-VLAN routing is configured on a Layer 3 switch with switched virtual interfaces for all three VLANs. Which action should the administrator take first to isolate the problem?

Accepted Answer

Verify that the VLAN 40 SVI is up and has the correct IP address and subnet mask.. Because routing between VLAN 20 and VLAN 30 already works, the Layer 3 switch is functioning as a router. The fault is specific to VLAN 40, so the logical first check is whether its switched virtual interface is up and correctly addressed. An SVI stays down when the VLAN has no active member ports or when the VLAN itself has not been created.

Answer

Reconfigure the default gateway on all hosts in VLAN 20 to point to the VLAN 40 SVI address.

Answer

Replace the Layer 3 switch with a router that has physical interfaces for each VLAN.

Answer

Disable inter-VLAN routing and rely on Layer 2 flooding to deliver traffic between VLANs.

Question 7

A network administrator is configuring a switch port that connects to a server. The administrator wants to ensure that the port does not participate in Spanning Tree Protocol (STP) and immediately transitions to the forwarding state when the link comes up. Which feature should be configured on this port?

Accepted Answer

PortFast. PortFast is the correct feature because it allows an access port to skip the STP listening and learning states and go straight to forwarding, which is ideal for server connections. BPDU Guard, Root Guard, and Loop Guard are STP enhancement features that protect the topology but do not provide immediate forwarding.

Answer

Root Guard

Answer

Loop Guard

Answer

BPDU Guard

Question 8

A network technician is troubleshooting intermittent connectivity to a server. The technician suspects a duplex mismatch on a switch port connected to the server. Which command should be used to check the duplex setting and error statistics on the switch port?

Accepted Answer

show interfaces gigabitEthernet 0/1. A duplex mismatch often causes late collisions, FCS errors, and runts on the side configured for half-duplex. The show interfaces command provides duplex mode and error counters for a specific interface. By examining these statistics, the technician can confirm whether a mismatch exists and take corrective action, such as setting both sides to auto-negotiate or matching duplex settings manually.

Answer

show cdp neighbors gigabitEthernet 0/1

Answer

show controllers gigabitEthernet 0/1

Answer

show ip interface gigabitEthernet 0/1

Question 9

Refer to the exhibit. A workstation is experiencing intermittent connectivity and slow network speeds. Based on the provided CLI output, what is the most likely cause of the performance issue?

Accepted Answer

A duplex mismatch between the switch and the host. A duplex mismatch occurs when one side of a link is set to full-duplex while the other is set to half-duplex. This leads to the half-duplex side detecting collisions late in the frame transmission process, while the full-duplex side records CRC errors because the incoming frames are interrupted or corrupted by the collision attempts.

Answer

A faulty SFP module in the switch

Answer

Excessive cable length beyond 100 meters

Answer

Electromagnetic interference from nearby power lines

Question 10

A technician is terminating a UTP cable. One end is terminated using the T568A standard, and the other end is terminated using the T568B standard. What type of cable has been created?

Accepted Answer

Crossover cable. A crossover cable is created when one end uses T568A pinout and the other uses T568B, which swaps the transmit and receive pairs (pins 1&2 with 3&6). This allows two like devices (e.g., switch-to-switch or PC-to-PC) to communicate without a crossover-capable port. The mismatched standards on each end is the defining characteristic of a crossover cable.

Answer

Straight-through cable

Answer

Rollover cable

Answer

Console cable

Question 11

Which feature is best suited to prevent VLAN hopping attacks where an attacker sends double-tagged 802.1Q frames to reach a restricted VLAN?

Accepted Answer

Disabling DTP and setting ports to 'switchport mode access'.. VLAN hopping via double-tagging occurs when an attacker sends a frame with two tags to a switch, tricking it into bypassing port restrictions. By explicitly configuring ports as access ports and disabling DTP negotiation, administrators prevent the switch from automatically forming trunks with unauthorized devices. This is a critical hardening step because it removes the possibility of a device negotiating a trunk link, which is required for VLAN hopping to succeed.

Answer

Implementing a standard Access Control List.

Answer

Configuring PortFast on all access ports.

Answer

Enabling VTP pruning on the switch.

Question 12

When connecting a modern PC directly to a modern Cisco switch port, the technician uses a standard straight-through cable and the link comes up immediately. Which feature enabled this connection to work?

Accepted Answer

Auto-MDIX. Historically, connecting like-devices required crossover cables, while unlike-devices used straight-through cables. Modern networking equipment simplifies this with a feature that automatically detects the required cable type and adjusts the internal transmit and receive pairs accordingly, allowing for greater flexibility and fewer specialized cables in a technician's kit.

Answer

Full-Duplex Negotiation

Answer

PoE Autonegotiation

Answer

CSMA/CD

Question 13

Refer to the exhibit. A technician is verifying the hardware installed in a switch. What type of media is required to connect to the 'Te1/1/1' interface based on the SFP type shown?

Accepted Answer

Multi-mode fiber optic cable. The 'Te1/1/1' interface naming indicates a 10 Gigabit Ethernet port, and the SFP type shown in the exhibit is a multi-mode fiber SFP (typically with an OM3/OM4 LC connector and a wavelength like 850 nm). Multi-mode fiber is used for short-reach 10G connections up to ~300–400 m, which matches the SFP's design. Therefore, a multi-mode fiber optic cable is required.

Answer

Single-mode fiber optic cable

Answer

Category 6a copper cable

Answer

Twinaxial (DAC) copper cable

Question 14

An organization is upgrading its cabling infrastructure to support Gigabit Ethernet over a distance of 85 meters. Which twisted-pair cable category is the minimum requirement to reliably support 1000 Mbps speeds at this specific distance?

Accepted Answer

Category 5e (Cat5e). Selecting the correct copper cabling category is vital for meeting bandwidth requirements while adhering to distance limitations defined by TIA/EIA standards. Understanding the capabilities of different categories ensures that the network infrastructure can support modern data rates without signal degradation or excessive crosstalk, which could lead to retransmissions and degraded user experiences across the enterprise.

Answer

Category 3 (Cat3)

Answer

Category 5 (Cat5)

Answer

Category 2 (Cat2)

Question 15

Which TWO of the following are primary security benefits of implementing an Access Control List (ACL) on a Cisco router interface?

Accepted Answer

Restricting unauthorized network access. ACLs are essential tools for traffic filtering and network segmentation. By controlling which packets are permitted or denied based on source, destination, and protocol, administrators enforce security policies at the network edge or between VLANs. Understanding how ACLs manage traffic flow is critical for maintaining network integrity and preventing unauthorized data access, as they provide the fundamental mechanism for restricting communication between sensitive network segments in a controlled and highly audit-able manner.

Answer

Encrypting sensitive data traffic

Answer

Automatically updating firmware

Answer

Providing hardware redundancy

Cisco Certified Support Technician - Networking 100-150 practice test

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