200-301 Cisco Certified Network Associate (CCNA) Exam Dumps and Practice Test Questions Set 7 Q121-140

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Question 121: 

Which feature on a switch prevents unauthorized DHCP servers from assigning IP addresses?

A) Port Security
B) DHCP Snooping
C) STP
D) ARP Inspection

Answer: B

Explanation: 

DHCP Snooping differentiates trusted and untrusted ports, allowing only authorized DHCP servers to assign IP addresses and protecting against rogue DHCP servers.

In modern networks, ensuring that devices receive valid IP addresses from authorized sources is critical for maintaining security and proper network operation. Unauthorized or rogue DHCP servers can assign incorrect IP addresses, gateways, or DNS settings, leading to network disruptions, man-in-the-middle attacks, or denial of service. To prevent this, switches provide a security feature called DHCP Snooping.

DHCP Snooping works by distinguishing between trusted and untrusted ports on a switch. Trusted ports are typically connected to legitimate DHCP servers, while untrusted ports are connected to end-user devices. The switch monitors DHCP messages on untrusted ports and only allows DHCP replies from trusted sources to reach client devices. Any DHCP offer or acknowledgment coming from an untrusted port is dropped, effectively preventing rogue DHCP servers from distributing IP addresses. In addition, DHCP Snooping builds a binding table that records the MAC addresses, IP addresses, lease times, and port numbers of clients. This table can be used by other security features, such as Dynamic ARP Inspection, to further protect the network against spoofing attacks.

Other options in the list serve different purposes. Port Security limits access to a switch port by restricting the number of MAC addresses that can connect through that port. While it prevents unauthorized devices from connecting, it does not directly control which devices can assign IP addresses. STP, or Spanning Tree Protocol, is designed to prevent Layer 2 loops in a network with redundant links. It ensures a loop-free topology but does not provide DHCP protection. ARP Inspection, specifically Dynamic ARP Inspection (DAI), validates ARP packets to prevent ARP spoofing, which protects the network from man-in-the-middle attacks but does not handle IP address assignment.

By using DHCP Snooping, network administrators can ensure that only authorized DHCP servers assign IP addresses, protect clients from receiving incorrect network configurations, and strengthen overall network security. It is an essential feature in enterprise and campus networks where multiple devices and potential unauthorized servers may exist.

The correct answer is DHCP Snooping.

Question 122: 

Which IPv4 address is considered a loopback address?

A) 192.168.1.1
B) 127.0.0.1
C) 169.254.0.1
D) 255.255.255.255

Answer: B

Explanation: 

127.0.0.1 is the loopback address used to test the host’s TCP/IP stack without sending packets on the network.

IPv4 addresses are categorized into different types for specific purposes, including unicast, multicast, broadcast, and special-purpose addresses. One important special-purpose address is the loopback address, which allows a host to test its own TCP/IP stack without transmitting data over a physical network.

The loopback address is 127.0.0.1. When a host sends a packet to this address, the network stack processes it locally, effectively sending the packet back to itself. This is useful for testing and troubleshooting because it allows administrators to verify that the TCP/IP protocol suite is functioning correctly on the host without relying on external network connectivity. The entire 127.0.0.0/8 range is reserved for loopback purposes, meaning any address from 127.0.0.1 to 127.255.255.254 will loop back to the host itself. The loopback address is commonly used in network diagnostics tools like ping and traceroute, where sending traffic to 127.0.0.1 can confirm that the local networking stack is operational.

Other addresses listed serve different roles. The address 192.168.1.1 is a private IPv4 address commonly used for internal networks, such as home or office LANs. It is routable only within private networks and cannot be used to test the host itself. 169.254.0.1 is part of the Automatic Private IP Addressing (APIPA) range. Devices automatically assign addresses in the 169.254.0.0/16 range when a DHCP server is unavailable, enabling limited local network communication but not testing the host’s TCP/IP stack. 255.255.255.255 is the limited broadcast address used to send packets to all hosts on a local subnet. It is not intended for loopback testing and is discarded by routers to prevent it from being forwarded beyond the local network.

The correct answer is 127.0.0.1.

Question 123: 

Which type of IPv6 address is automatically configured for local communications on all interfaces?

A) Global unicast
B) Link-local
C) Multicast
D) Anycast

Answer: B

Explanation: 

Link-local addresses (FE80::/10) are automatically assigned to all IPv6 interfaces and are required for local link communication, including routing protocols and neighbor discovery.

IPv6 introduces several types of addresses, each serving a specific purpose in network communication. One of the most fundamental IPv6 addresses is the link-local address, which is automatically assigned to all interfaces and plays a crucial role in local network operations.

Link-local addresses use the prefix FE80::/10 and are automatically configured on every IPv6-enabled interface, even if no other addresses are manually assigned or obtained via DHCPv6. These addresses are essential for communication between nodes on the same physical or logical link. They are required for core IPv6 functions such as neighbor discovery, which allows devices to determine the link-layer addresses of other nodes on the same link, and for routing protocols, which often rely on link-local addresses to exchange routing information between adjacent routers. Because link-local addresses are only valid within a single link, they cannot be routed across different networks, making them ideal for local communications.

Other IPv6 address types have different roles. Global unicast addresses are globally routable and reachable on the IPv6 internet. They are equivalent to public IPv4 addresses and are used for communication between devices across the internet. Multicast addresses are used for one-to-many communication, delivering packets to all nodes that have joined a specific multicast group. Multicast is important for functions like streaming, network discovery, or routing updates. Anycast addresses are assigned to multiple interfaces, often on different devices, but packets sent to an anycast address are delivered to the nearest interface based on routing metrics. Anycast is used for redundancy and load balancing but is not automatically assigned to all interfaces.

In summary, link-local addresses are the only IPv6 address type automatically configured on all interfaces. They are critical for local communications, supporting neighbor discovery, local routing protocols, and other link-specific operations. Without link-local addresses, basic IPv6 functionality within a local segment would not be possible.

The correct answer is link-local.

Question 124: 

Which command on a Cisco router displays the neighbor routers learned through OSPF?

A) show ip route ospf
B) show ip ospf neighbor
C) show running-config
D) show ip interface brief

Answer: B

Explanation: 

show ip ospf neighbor lists all OSPF neighbors, their state (e.g., FULL), IP addresses, and interface associations.

Open Shortest Path First (OSPF) is a widely used link-state routing protocol that allows routers to exchange routing information within an autonomous system. Establishing and maintaining neighbor relationships is a core function of OSPF, as routers need to communicate with adjacent routers to share link-state information and build a consistent view of the network topology. Cisco routers provide several commands to monitor and troubleshoot OSPF, each serving different purposes.

The command show ip ospf neighbor is specifically designed to display information about OSPF neighbors learned by the router. When executed, this command lists all neighboring routers, their current state in the OSPF adjacency process, the IP addresses associated with each neighbor, and the interfaces through which the neighbors are reachable. Common states include INIT, TWO-WAY, and FULL, with FULL indicating that the routers have successfully exchanged link-state information and can now participate fully in OSPF routing. This command is essential for verifying that OSPF adjacencies are functioning correctly, identifying potential communication issues between routers, and confirming that routing updates can be exchanged properly.

Other commands provide different types of information. show ip route ospf displays the OSPF-learned routes that are installed in the router’s IP routing table, showing the networks reachable via OSPF, their next-hop addresses, and the outgoing interfaces. While useful for route verification, it does not provide details about neighbor relationships. show running-config shows the active configuration on the router, including OSPF network statements and interface settings, but it does not provide real-time information about neighbor states. show ip interface brief displays a summary of all interfaces, their IP addresses, and operational status, which is helpful for general interface troubleshooting but does not provide OSPF neighbor information.

In summary, show ip ospf neighbor is the correct command to verify OSPF neighbor relationships. It provides detailed, real-time information about adjacent routers, interface associations, and the states of OSPF adjacencies, which is critical for monitoring and troubleshooting OSPF in a network.

Question 125: 

A switch port configured with switchport mode access is connected to a single host. What type of traffic does it carry?

A) Traffic for all VLANs
B) Traffic for a single VLAN
C) Tagged and untagged VLAN traffic
D) Multicast only

Answer: B

Explanation: 

Access ports carry traffic for a single VLAN and do not tag frames. Trunk ports are used to carry multiple VLANs.

In Ethernet networks, switch ports can be configured in different modes to manage how traffic is forwarded and segmenteD) One of the most common configurations is the access port, which is used to connect a single host, such as a computer, printer, or IP phone, to the network. An access port is configured using the command switchport mode access and is associated with a specific VLAN.

Traffic on an access port is restricted to a single VLAN. When a device connected to an access port sends a frame, the switch forwards it only within the assigned VLAN. Frames received on this port are not tagged with VLAN information because access ports operate at Layer 2 without tagging. This makes access ports ideal for end-user devices that do not need to be aware of VLANs. By contrast, trunk ports are used to carry traffic for multiple VLANs over a single physical link. Trunk ports tag frames with VLAN identifiers using protocols such as IEEE 802.1Q, allowing switches and routers to distinguish traffic for different VLANs and maintain network segmentation across multiple switches.

Other options in the context of this question serve different purposes. Traffic for all VLANs is carried only on trunk ports, not access ports. Tagged and untagged VLAN traffic is typically handled on trunk ports with native VLANs or on ports configured for dynamic trunking, not on standard access ports. Multicast traffic can exist on any port, but access ports are not limited to multicast; they carry all traffic types (unicast, broadcast, and multicast) for the assigned VLAN.

By understanding that a switch port in access mode is tied to a single VLAN, network administrators can ensure proper network segmentation, enforce security policies, and simplify troubleshooting. Access ports provide a straightforward method for connecting hosts while maintaining the VLAN structure of the network, ensuring that traffic is contained within its designated VLAN and does not inadvertently traverse other VLANs.

Question 126: 

Which type of routing protocol uses hop count as its only metric?

A) OSPF
B) RIP
C) EIGRP
D) BGP

Answer: B

Explanation: 

RIP is a distance-vector routing protocol that uses hop count as its metric, with a maximum of 15 hops; networks beyond 15 hops are considered unreachable.

Routing protocols are essential for determining the best path for data to travel across a network. Different routing protocols use different metrics and algorithms to evaluate paths, influencing how traffic is routeD) Among these protocols, the Routing Information Protocol (RIP) is a classic example that relies on a simple metric called hop count.

RIP is a distance-vector routing protocol that uses hop count as its only metric to determine the best path to a destination network. Each router that forwards a packet is considered one hop. RIP calculates the total number of hops to reach a destination and selects the path with the lowest hop count. However, RIP has a limitation: it supports a maximum of 15 hops. Networks that require more than 15 hops are considered unreachable, making RIP suitable primarily for smaller networks. RIP periodically shares its routing table with neighboring routers, which can lead to slower convergence compared to more advanced protocols, and it may be prone to routing loops without additional mechanisms such as split horizon and hold-down timers.

Other routing protocols use different approaches. OSPF, or Open Shortest Path First, is a link-state protocol that calculates the shortest path based on cost, which can take into account bandwidth and other interface metrics, rather than just hop count. EIGRP, or Enhanced Interior Gateway Routing Protocol, is a hybrid protocol that uses a combination of metrics including bandwidth, delay, load, and reliability to determine the best path. BGP, or Border Gateway Protocol, is an exterior gateway protocol that uses path attributes, such as AS path, to make routing decisions, and it is primarily used for routing between autonomous systems on the internet.

In summary, RIP is unique among these options because it relies solely on hop count as its metriC) While simple to configure and easy to understand, its limitations make it less suitable for large or complex networks compared to OSPF, EIGRP, or BGP. RIP’s simplicity, however, remains valuable for small, uncomplicated network environments.

Question 127: 

Which command on a switch shows the MAC addresses learned and the associated ports?

A) show interfaces
B) show mac-address-table
C) show vlan brief
D) show ip route

Answer: B

Explanation: 

show mac-address-table lists all MAC addresses learned by the switch and the ports through which they were learned, useful for Layer 2 troubleshooting.

In a switched network, understanding how a switch learns and forwards traffic at Layer 2 is crucial for troubleshooting and network management. Switches maintain a MAC address table, also known as a forwarding table or CAM table, which maps MAC addresses to the switch ports on which they were learneD) This table allows the switch to efficiently forward frames to the correct destination port rather than flooding them to all ports.

The command show mac-address-table on a Cisco switch is used to display the MAC addresses learned by the switch and the corresponding ports through which each address was observeD) When executed, the command provides a list of MAC addresses, the VLAN associated with each address, and the specific port where the device is connecteD) This information is invaluable for network administrators to verify connectivity, identify where devices are located in the network, and troubleshoot issues such as incorrect VLAN assignments, duplicate MAC addresses, or unexpected flooding. For example, if a host is not reachable, reviewing the MAC address table can confirm whether the switch has learned the host’s MAC address and whether it is associated with the correct port.

Other commands serve different purposes. show interfaces provides detailed information about each interface’s operational status, speed, duplex settings, and error statistics, which is helpful for physical connectivity troubleshooting but does not show MAC address associations. show vlan brief displays the VLANs configured on the switch, their status, and which ports are assigned to each VLAN. While this helps in verifying VLAN configurations, it does not indicate which MAC addresses are actively learned on those ports. show ip route shows the router or switch’s Layer 3 routing table and the networks it can reach. This command is useful for Layer 3 troubleshooting but does not provide Layer 2 MAC address information.

In summary, show mac-address-table is the specific command used to view all MAC addresses learned by a switch and the associated ports. It is an essential tool for Layer 2 network monitoring, verification, and troubleshooting.

Question 128: 

Which feature allows multiple physical links to be combined as one logical link for redundancy and higher bandwidth?

A) STP
B) EtherChannel
C) VLAN trunking
D) HSRP

Answer: B

Explanation: 

EtherChannel aggregates multiple physical links into a single logical link, increasing bandwidth and providing redundancy while maintaining a single interface for configuration.

In modern network design, ensuring both high availability and sufficient bandwidth between switches or between a switch and a router is critical. One effective method to achieve this is by combining multiple physical links into a single logical connection. This capability is provided by EtherChannel, a feature commonly implemented on Cisco switches.

EtherChannel allows multiple physical Ethernet links to be bundled together, creating one logical interface. This aggregated link provides several benefits. First, it increases overall bandwidth between devices, as traffic can be distributed across all the physical links in the bundle using load-balancing methods based on source and destination IP addresses, MAC addresses, or Layer 4 port numbers. Second, EtherChannel provides redundancy. If one of the physical links in the bundle fails, the traffic is automatically redistributed across the remaining active links, maintaining connectivity without causing network downtime. From the administrator’s perspective, all physical links in the bundle appear as a single logical interface, which simplifies configuration and management. EtherChannel can be configured manually as a static bundle or dynamically using protocols such as PAgP (Port Aggregation Protocol) or LACP (Link Aggregation Control Protocol).

Other options provide different functionalities. STP, or Spanning Tree Protocol, is used to prevent loops in Layer 2 networks by selectively blocking redundant paths. While STP ensures loop-free topologies, it does not aggregate multiple links to increase bandwidth. VLAN trunking allows multiple VLANs to share a single physical connection by tagging frames with VLAN identifiers, enabling inter-VLAN communication across switches, but it does not provide redundancy or bandwidth aggregation. HSRP, or Hot Standby Router Protocol, is designed for router redundancy. It allows multiple routers to act as a single virtual gateway, ensuring failover in case one router fails, but it does not combine multiple physical links to increase bandwidth.

In summary, EtherChannel is the feature that enables multiple physical links to function as one logical interface, providing both higher bandwidth and redundancy. It is widely used in enterprise networks to enhance performance and resilience.

Question 129: 

Which protocol provides encrypted management access to network devices?

A) Telnet
B) SSH
C) FTP
D) HTTP

Answer: B

Explanation: 

SSH encrypts traffic between the management workstation and network device, securing login credentials and commands. Telnet, in contrast, sends data in plaintext.

Managing network devices securely is a critical aspect of network administration. Network administrators often need to access routers, switches, firewalls, and other devices remotely to configure settings, troubleshoot issues, or monitor performance. However, transmitting sensitive information like login credentials and configuration commands over the network can be risky if the data is not encrypteD) Secure Shell (SSH) addresses this concern by providing encrypted management access to network devices.

SSH establishes a secure, encrypted session between a management workstation and the network device. All traffic, including usernames, passwords, and command-line instructions, is encrypted, protecting it from eavesdropping or interception by unauthorized users. This makes SSH the preferred method for remote management of network devices. SSH also supports authentication using passwords or cryptographic keys, adding an additional layer of security compared to traditional methods.

Other protocols listed provide remote access or file transfer but lack encryption. Telnet is a legacy protocol that allows remote access to network devices, but it transmits data in plaintext. This means that anyone monitoring the network can capture usernames, passwords, and commands, making it insecure for modern networks. FTP, or File Transfer Protocol, is used to transfer files between devices. While FTP enables uploading and downloading configuration files or software images, it also transmits credentials and data in plaintext, posing security risks. HTTP is a protocol used for accessing web-based interfaces on devices, but standard HTTP does not provide encryption. This means that web-based login credentials and configuration changes sent over HTTP can be intercepteD) HTTPS, the secure version of HTTP, solves this by encrypting traffiC)

In summary, SSH is the protocol designed for secure, encrypted management access to network devices. Unlike Telnet, FTP, or HTTP, it protects sensitive information during remote sessions, ensuring confidentiality and integrity. For modern network environments, SSH is the standard method for secure device administration.

Question 130: 

Which command on a router verifies the IP address, operational status, and protocol state of all interfaces?

A) show ip route
B) show ip interface brief
C) show running-config
D) show vlan brief

Answer: B

Explanation: 

show ip interface brief provides a concise summary of all interfaces, their IP addresses, and operational and protocol status, useful for verifying interface configurations.

In network management, verifying the status and configuration of router interfaces is a fundamental task. Interfaces are the points through which a router connects to networks, and ensuring they are properly configured and operational is critical for network connectivity. Cisco routers provide several commands for monitoring interface status, but show ip interface brief is one of the most commonly used for quick verification.

The command show ip interface brief displays a concise summary of all interfaces on the router. It shows the interface name, the IP address assigned to it, and two important status indicators: the operational status (whether the interface is administratively up or down) and the protocol status (whether the line protocol is up or down). This information allows network administrators to quickly identify interfaces that are misconfigured, down, or experiencing connectivity issues. For example, an interface may be physically connected (line protocol up) but administratively shut down, which can be easily detected using this commanD)

Other commands provide complementary information but are less focused on interface verification. show ip route displays the router’s IP routing table, showing networks the router can reach, next-hop addresses, and outgoing interfaces. While this is useful for verifying reachability and route propagation, it does not provide a clear view of the operational state of each interface. show running-config shows the router’s active configuration, including interface settings, IP addresses, and other parameters. This command is useful for configuration review but requires manually checking each interface’s configuration and does not indicate real-time operational status. show vlan brief is specific to switches and displays VLANs, their status, and the ports assigned to each VLAN. It is not applicable for verifying router interface IP addresses or protocol states.

In summary, show ip interface brief is the optimal command for quickly verifying the IP address, operational status, and protocol state of all interfaces on a router. It provides a concise and real-time overview that is essential for troubleshooting connectivity issues and ensuring proper network operation.

Question 131: 

Which type of IPv6 address allows multiple devices to share the same address for routing purposes, with packets delivered to the nearest device?

A) Unicast
B) Multicast
C) Anycast
D) Link-local

Answer: C

Explanation: 

Anycast addresses allow multiple devices to share the same IPv6 address. Routers deliver packets to the nearest device based on routing metrics.

Question 132: 

Which protocol is used to dynamically assign IP addresses and other network information to hosts?

A) DHCP
B) ARP
C) ICMP
D) DNS

Answer: A

Explanation: 

DHCP automatically assigns IP addresses, subnet masks, default gateways, and DNS server information to hosts, reducing manual configuration errors.

In modern networks, assigning IP addresses and other network configuration information to hosts is a critical task for ensuring proper communication. While it is possible to manually configure IP addresses, doing so on large networks is time-consuming and prone to errors. To simplify this process, the Dynamic Host Configuration Protocol (DHCP) is useD)

DHCP is a network management protocol that automatically assigns IP addresses, subnet masks, default gateways, and DNS server information to hosts when they join a network. When a device connects, it sends a DHCP discovery message requesting network configuration. A DHCP server responds with an offer that includes an available IP address and other necessary configuration details. The host then requests the offered IP address, and the server acknowledges it, completing the lease process. This dynamic assignment ensures that each host receives a unique IP address and reduces the likelihood of conflicts caused by duplicate addresses. DHCP also allows centralized management of IP address allocation, making it ideal for networks where devices frequently join or leave.

Other protocols listed serve different purposes and do not provide IP address assignment. ARP, or Address Resolution Protocol, maps IP addresses to MAC addresses within a local network, allowing devices to communicate at Layer 2, but it does not assign IP addresses. ICMP, or Internet Control Message Protocol, is used for sending error messages and operational information related to IP processing, such as unreachable hosts or time exceeded messages. ICMP is essential for network diagnostics but does not handle network configuration. DNS, or Domain Name System, translates human-readable domain names into IP addresses, allowing users to access websites without remembering numerical addresses, but it does not provide IP configuration to hosts.

In summary, DHCP is the protocol specifically designed to dynamically assign IP addresses and other network configuration information to hosts. By automating this process, DHCP improves efficiency, reduces configuration errors, and enables devices to join networks seamlessly without requiring manual setup.

Question 133: 

A network engineer wants to block traffic from a specific IP address range. Which ACL type should be used?

A) Standard ACL
B) Extended ACL
C) Reflexive ACL
D) Named ACL

Answer: B

Explanation: 

Extended ACLs allow filtering based on source and destination IP addresses, protocols, and port numbers. Standard ACLs can only filter by source IP.

Question 134: 

Which command displays the OSPF routing table on a Cisco router?

A) show ip route ospf
B) show ip ospf neighbor
C) show ip interface brief
D) show running-config

Answer: A

Explanation: 

show ip route ospf displays all routes learned via OSPF, including prefixes, next hops, and interfaces used to reach destinations.

Open Shortest Path First (OSPF) is a widely used link-state routing protocol that enables routers to share routing information efficiently within an autonomous system. OSPF calculates the shortest path to each network using the Dijkstra algorithm and maintains a routing table that determines how packets are forwardeD) Cisco routers provide several commands to monitor and troubleshoot OSPF, each providing different levels of information.

The command show ip route ospf is specifically designed to display all routes that a router has learned via OSPF and has installed in its IP routing table. When executed, it lists the destination network prefixes, the next-hop addresses to reach those networks, and the outgoing interfaces that will be used for packet forwarding. This information is essential for network administrators to verify that OSPF is functioning correctly, that routes are being properly learned from neighboring routers, and that traffic will take the expected paths through the network. It also helps identify missing or incorrect routes, which can indicate misconfigurations, neighbor relationship issues, or other network problems.

Other commands serve different purposes. show ip ospf neighbor displays information about OSPF neighbor routers, including their IP addresses, interface associations, and the state of the adjacency, such as INIT, TWO-WAY, or FULL. This command is useful for verifying OSPF neighbor relationships but does not provide routing table information. show ip interface brief provides a concise summary of all interfaces, their IP addresses, and operational and protocol status, which is useful for interface verification but does not display learned OSPF routes. show running-config shows the router’s active configuration, including OSPF network statements, interface IP addresses, and other settings, but it does not show real-time routing table entries.

In summary, show ip route ospf is the command that provides a complete view of all OSPF-learned routes in the routing table, including next hops and outgoing interfaces. It is essential for monitoring OSPF operations and troubleshooting routing issues.

Question 135: 

Which protocol is used for sending error messages, such as “host unreachable” or “time exceeded”?

A) ICMP
B) ARP
C) DNS
D) DHCP

Answer: A

Explanation: 

ICMP is used by routers and hosts to report network errors and operational information, such as unreachable destinations or TTL expiration.

The Internet Control Message Protocol (ICMP) is a fundamental protocol within the Internet Protocol (IP) suite, used to report errors and provide operational information about network communication. Unlike protocols such as TCP or UDP, which are used to transport data between applications, ICMP is designed to deliver control and error messages between hosts and routers.

ICMP plays a critical role in network troubleshooting and diagnostics. For example, when a router receives a packet destined for a host that it cannot reach, it generates an ICMP “host unreachable” message and sends it back to the source. Similarly, if a packet’s Time-to-Live (TTL) expires before reaching its destination, the router discards the packet and sends an ICMP “time exceeded” message to inform the sender that the packet could not be delivereD) These messages help administrators and network applications understand connectivity issues and adjust accordingly. ICMP is also widely used in diagnostic tools such as ping, which sends ICMP echo requests to test connectivity, and traceroute, which uses ICMP messages to determine the path packets take through the network.

Other protocols listed serve very different functions. ARP, or Address Resolution Protocol, operates at Layer 2 and maps IP addresses to MAC addresses within a local network. ARP does not provide error reporting or operational feedback beyond local address resolution. DNS, or Domain Name System, translates human-readable domain names into IP addresses, enabling users to access websites without memorizing numeric addresses, but it does not generate network error messages. DHCP, or Dynamic Host Configuration Protocol, dynamically assigns IP addresses and network configuration information to hosts, but it is not involved in reporting errors during packet delivery.

Question 136: 

Which Layer 2 protocol detects redundant paths and prevents loops in a network?

A) RIP
B) STP
C) OSPF
D) BGP

Answer: B

Explanation: 

STP (Spanning Tree Protocol) detects redundant Layer 2 paths and blocks some ports to prevent loops while maintaining at least one active path.

In switched networks, redundant links are often implemented to provide fault tolerance and ensure that connectivity is maintained if a primary link fails. While redundancy improves network reliability, it also introduces the risk of loops at Layer 2. Loops can cause broadcast storms, excessive CPU utilization on switches, and overall network instability. To address this issue, the Spanning Tree Protocol (STP) is useD)

STP is a Layer 2 protocol that detects redundant paths in a network and prevents loops by selectively blocking some of the redundant links. When STP is enabled on switches, it elects a root bridge, which serves as a reference point for all path calculations. STP then determines the shortest path from each switch to the root bridge and assigns port roles, such as root port, designated port, or blocked port. Root ports are used to reach the root bridge, designated ports forward traffic for a particular segment, and blocked ports prevent frames from circulating endlessly. By keeping at least one active path while blocking others, STP ensures a loop-free topology, allowing redundant links to be used only if an active path fails.

Other protocols listed operate at Layer 3 or serve different purposes. RIP, or Routing Information Protocol, is a distance-vector routing protocol used to exchange routing information between routers based on hop count, and it does not address Layer 2 loops. OSPF, or Open Shortest Path First, is a link-state routing protocol that calculates the shortest paths to networks using metrics such as cost. OSPF operates at Layer 3 and manages routing tables but does not prevent Layer 2 loops. BGP, or Border Gateway Protocol, is an exterior gateway protocol used to exchange routing information between autonomous systems on the internet. BGP focuses on policy-based path selection at Layer 3 and is not concerned with Layer 2 topology or loop prevention.

Question 137: 

Which command verifies the status of a trunk interface and allowed VLANs on a Cisco switch?

A) show vlan brief
B) show interfaces trunk
C) show running-config
D) show spanning-tree

Answer: B

Explanation: 

show interfaces trunk shows trunk ports, allowed VLANs, native VLAN, and encapsulation, helping troubleshoot VLAN trunking issues.

In a network with multiple VLANs, switches often use trunk ports to carry traffic for more than one VLAN across a single physical link. Proper configuration and verification of trunk ports are essential to ensure that VLAN traffic is forwarded correctly between switches and other network devices. Cisco switches provide commands to monitor and troubleshoot trunking, with show interfaces trunk being the most specific for verifying trunk status.

The command show interfaces trunk displays information about all trunk interfaces on a switch. It lists the trunk ports, their operational status, the encapsulation type (such as 802.1Q), the native VLAN, and the VLANs that are allowed across the trunk. This command helps network administrators verify that the trunk is properly configured and operational. For example, if a VLAN is not passing traffic as expected, this command can reveal whether the VLAN is included in the allowed VLAN list or if the trunk itself is down. By providing detailed trunk information, show interfaces trunk is an essential tool for troubleshooting VLAN connectivity issues and ensuring that traffic is correctly segmented and forwardeD)

Other commands serve different purposes but do not provide as much trunk-specific information. show vlan brief displays a summary of all VLANs configured on the switch, their status, and the ports assigned to each VLAN. While useful for verifying VLAN assignments, it does not show trunk configuration details, allowed VLANs, or encapsulation. show running-config shows the active configuration of the switch, including interface configurations, VLAN settings, and trunk commands, but it requires manual inspection to verify trunk operation and does not display real-time status. show spanning-tree provides information about Spanning Tree Protocol, including port roles and states to prevent loops, but it does not indicate which VLANs are allowed on trunk ports or their operational status.

In summary, show interfaces trunk is the command that specifically verifies trunk interface status, allowed VLANs, native VLAN, and encapsulation type. It provides a concise and accurate overview of trunk operation, making it indispensable for managing VLAN traffic across switch links.

Question 138: 

Which type of ACL filters traffic only by source IP address?

A) Standard ACL
B) Extended ACL
C) Reflexive ACL
D) Named ACL

Answer: A

Explanation: 

Standard ACLs filter traffic based solely on the source IP address, providing basic control over which devices can communicate through the router or interface.

Access Control Lists (ACLs) are a fundamental tool in networking for controlling the flow of traffic through routers and switches. They allow administrators to permit or deny packets based on specific criteria, enhancing security and traffic management. ACLs come in various types, each providing different levels of filtering granularity.

Standard ACLs are the simplest type of ACL. They filter traffic solely based on the source IP address of the packets. When a packet arrives at a router or interface with a standard ACL applied, the device compares the source IP address against the rules in the ACL. If the source IP matches a permit statement, the packet is allowed to pass; if it matches a deny statement, the packet is blockeD) Because standard ACLs do not examine destination IP addresses, protocol types, or port numbers, they provide basic but effective control over which devices are allowed to communicate across a network. Standard ACLs are typically applied close to the destination of the traffic to minimize the risk of unintentionally blocking important communication.

Extended ACLs offer more advanced filtering. In addition to source IP addresses, extended ACLs can filter based on destination IP addresses, protocol types (such as TCP, UDP, or ICMP), and port numbers. This allows for more precise traffic control, such as permitting HTTP traffic from a specific network while blocking other types of traffiC)

In summary, standard ACLs are used when filtering traffic by source IP address alone is sufficient. They provide basic security and control, ensuring that only designated devices can access certain network segments. While extended, reflexive, and named ACLs offer more features, standard ACLs remain a straightforward and effective method for simple access control.

Question 139: 

Which protocol is used to translate domain names to IP addresses?

A) DHCP
B) ARP
C) DNS
D) ICMP

Answer: C

Explanation: 

DNS resolves human-readable hostnames to IP addresses, enabling devices to communicate using names instead of numeric addresses.

In modern networks, users typically interact with services and websites using human-readable names, such as www.example.com, rather than numerical IP addresses. However, computers and network devices communicate using IP addresses. To bridge this gap, the Domain Name System (DNS) is useD)

DNS is a hierarchical, distributed naming system that translates domain names into IP addresses, allowing devices to locate and communicate with each other across the internet or private networks. When a user enters a domain name in a web browser, the computer sends a DNS query to a DNS server. The server responds with the corresponding IP address, which the device then uses to establish a connection. Without DNS, users would need to memorize and enter numerical IP addresses for every website or network service, which is impractical and error-prone. DNS also supports reverse resolution, translating IP addresses back into domain names, which is useful for logging, troubleshooting, and security applications.

Other protocols listed serve different purposes and do not perform name resolution. DHCP, or Dynamic Host Configuration Protocol, automatically assigns IP addresses and other network configuration information to hosts, such as subnet masks, default gateways, and DNS server addresses. While DHCP can provide the address of a DNS server to hosts, it does not perform the actual translation of names to IP addresses. ARP, or Address Resolution Protocol, maps IP addresses to MAC addresses within a local network, allowing devices to communicate at Layer 2, but it does not resolve domain names. ICMP, or Internet Control Message Protocol, is used for reporting errors and operational information, such as unreachable hosts or TTL expiration, and is also used by diagnostic tools like ping, but it does not provide address resolution.

In summary, DNS is the protocol specifically designed to translate human-readable domain names into IP addresses, enabling seamless communication between devices on a network. It is an essential component of both internet and internal network functionality, simplifying user interactions and supporting efficient network operations.

Question 140: 

Which protocol allows monitoring of network devices and generates alerts for abnormal events?

A) FTP
B) SNMP
C) ICMP
D) ARP

Answer: B

Explanation: 

SNMP (Simple Network Management Protocol) allows administrators to monitor devices, collect statistics, and receive notifications (traps) for network issues or abnormal behavior.