200-301 Cisco Certified Network Associate (CCNA) Exam Dumps and Practice Test Questions Set 8 Q141-160

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Question 141: 

Which feature allows a switch to prevent unauthorized devices from sending traffic through a port?

A) STP
B) Port Security
C) DHCP Snooping
D) EtherChannel

Answer: B

Explanation: 

Port Security restricts access to a switch port based on allowed MAC addresses and can shut down, restrict, or protect the port if an unauthorized device attempts to connect.

In a network environment, controlling access to switch ports is critical for maintaining security and preventing unauthorized devices from connecting and sending traffic. Switches provide a feature called port security to address this need.

Port Security allows network administrators to restrict access to a switch port based on the MAC addresses of connected devices. When a port is configured with port security, the switch can be set to allow a specific number of MAC addresses or even a predefined set of addresses. If an unauthorized device attempts to connect to the port, the switch can respond in one of several ways: it can shut down the port entirely, place the port into a restricted state where only authorized traffic is allowed, or simply drop traffic from the unauthorized device while keeping the port active. This helps prevent network breaches, rogue devices, and potential attacks such as MAC flooding. Port security is particularly useful in environments like offices, classrooms, or data centers, where physical access to network ports is possible but must be controlled.

Other options listed provide different types of network functionality. STP, or Spanning Tree Protocol, is used to prevent loops in Layer 2 networks by selectively blocking redundant paths but does not control which devices can connect to a port. DHCP Snooping is a security feature that differentiates between trusted and untrusted ports to prevent rogue DHCP servers from assigning IP addresses, but it does not prevent unauthorized devices from sending other types of traffic. EtherChannel aggregates multiple physical links into a single logical link to provide higher bandwidth and redundancy, but it does not provide access control for individual devices.

In summary, port security is the feature that enables a switch to control access based on MAC addresses, ensuring that only authorized devices can send traffic through a port. It provides flexibility in handling violations and is a key component of Layer 2 network security, protecting against unauthorized access and potential network attacks.

Question 142: 

Which command displays the interfaces on a router along with their IP addresses and operational status?

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

Answer: B

Explanation: 

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

In network administration, verifying the status and configuration of router interfaces is essential for ensuring proper connectivity and troubleshooting issues. Cisco routers provide several commands for monitoring interfaces, but one of the most commonly used for quickly obtaining a summary of interface information is show ip interface brief.

The show ip interface brief command provides a concise overview of all interfaces on the router, including key information such as the interface name, IP address assigned, and both the operational status and protocol status. The operational status indicates whether the interface is administratively up or down, while the protocol status reflects whether the line protocol is active. This distinction is important because an interface can be physically enabled but may not be operational due to configuration issues or Layer 2 problems. By providing this information in a compact format, the command allows network administrators to quickly verify IP address assignments, identify interfaces that are down, and detect misconfigurations without needing to examine detailed interface statistics.

Other commands provide complementary information but do not give the same level of interface summary. show running-config displays the router’s active configuration, including IP addresses, interface settings, routing protocols, and other configurations. While useful for reviewing how interfaces are configured, it does not indicate real-time operational status. show ip route shows the routing table, including learned routes and the associated outgoing interfaces. It is helpful for verifying network reachability but does not give a direct view of interface states. show vlan brief is primarily used on switches to display VLANs, their status, and the ports assigned to each VLAN; it is not applicable for viewing router interface details.

In summary, show ip interface brief is the most efficient command for verifying the IP addresses, operational status, and protocol states of all interfaces on a router. It provides a quick, real-time view that is crucial for troubleshooting connectivity issues and ensuring that interfaces are correctly configured and functioning as expecteD)

Question 143: 

Which protocol assigns IP addresses to hosts automatically?

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

Answer: B

Explanation: 

DHCP automates IP configuration for hosts, including subnet masks, default gateways, and DNS servers, reducing manual configuration errors.In modern networks, each device requires an IP address and additional network configuration to communicate effectively. Manually assigning IP addresses to each host can be time-consuming, prone to errors, and difficult to manage in large networks. To address this, the Dynamic Host Configuration Protocol (DHCP) is used to automatically assign IP addresses and related network settings to hosts.

DHCP works by dynamically providing IP configuration to devices when they join a network. When a host connects, it broadcasts a DHCP discovery message requesting network settings. The DHCP server responds with a DHCP offer that includes an available IP address, subnet mask, default gateway, and DNS server information. The host then requests the offered address, and the server confirms it, completing the lease process. This automation ensures that each device receives a unique IP address and the correct network settings, significantly reducing the risk of conflicts and misconfigurations. DHCP also simplifies network management by centralizing IP address allocation, making it easier to manage dynamic and growing networks.

Other protocols listed serve different purposes and do not assign IP addresses. ARP, or Address Resolution Protocol, maps IP addresses to MAC addresses within a local network, enabling devices to communicate at Layer 2, but it does not provide IP addresses. DNS, or Domain Name System, resolves human-readable domain names into IP addresses, allowing users to access websites without memorizing numeric addresses, but it does not assign IP addresses to hosts. ICMP, or Internet Control Message Protocol, is used for reporting network errors and operational information, such as unreachable hosts or time-to-live expiration, and is also used by diagnostic tools like ping and traceroute. ICMP is essential for troubleshooting and network diagnostics but does not perform IP configuration.

In summary, DHCP is the protocol designed specifically for automatically assigning IP addresses and network configuration information to hosts. By automating IP address assignment, DHCP reduces manual configuration errors, supports dynamic networks, and ensures that devices can seamlessly connect to and communicate across the network.

Question 144: 

Which IPv6 address type identifies a single interface for one-to-one communication?

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

Answer: A

Explanation: 

Unicast addresses in IPv6 identify a single interface, enabling one-to-one communication between devices.

In IPv6 networking, addresses are categorized into different types based on how packets are delivered across the network. One of the primary address types is the unicast address. Unicast addresses are designed to identify a single interface on a device, enabling one-to-one communication between two endpoints. When a packet is sent to a unicast address, it is delivered specifically to the interface assigned that address, making unicast the most common type of communication in IPv6 networks.

Unicast addresses can be global or link-local. Global unicast addresses are routable across the internet and are used for communication between devices on different networks. Link-local unicast addresses, which always start with the prefix FE80::/10, are automatically configured on all IPv6-enabled interfaces and are used for communication within the same link, such as for neighbor discovery or routing protocol operations. Regardless of scope, unicast addresses always represent a single destination interface, ensuring precise delivery of packets for direct communication.

Other IPv6 address types serve different purposes. Multicast addresses are used for one-to-many communication. A packet sent to a multicast address is delivered to all interfaces that have joined the corresponding multicast group, making it useful for tasks such as routing updates or streaming services. Anycast addresses are assigned to multiple interfaces, usually on different devices, but packets sent to an anycast address are delivered to the nearest interface according to routing metrics. Anycast is useful for redundancy and load balancing, but unlike unicast, it does not guarantee delivery to a single predetermined interface. Link-local addresses are automatically assigned to interfaces for local communications within a subnet and are required for certain network functions, but they can be unicast or multicast in nature.

In summary, unicast addresses in IPv6 identify a single interface for one-to-one communication, enabling direct and specific delivery of packets between devices. This makes unicast the foundational address type for most network interactions.

Question 145: 

Which command displays the MAC addresses learned by a switch and the ports they are associated with?

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 the switch has learned and the corresponding ports, useful for troubleshooting Layer 2 connectivity.

In a switched network, understanding how a switch learns and forwards traffic at Layer 2 is crucial for effective network management and troubleshooting. Switches use a MAC address table, also known as a forwarding table or CAM table, to map MAC addresses to specific switch ports. This table enables the switch to forward frames only to the appropriate destination port rather than flooding traffic to all ports, which improves efficiency and reduces unnecessary traffic on the network.

The command show mac-address-table on a Cisco switch is used to display all the MAC addresses that the switch has learned and the ports through which they were observeD) When executed, it provides a list of MAC addresses, the VLAN associated with each address, and the switch port where each device is connecteD) This information is invaluable for network administrators who need to verify connectivity, identify the physical location of devices, or troubleshoot Layer 2 issues. For instance, if a host is not reachable, 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. This helps pinpoint misconfigurations, incorrect VLAN assignments, or issues such as loops and duplicate MAC addresses.

Other commands provide complementary information but are not focused on Layer 2 MAC address tracking. show interfaces provides detailed interface statistics, including operational status, errors, speed, and duplex settings, which is useful for physical connectivity troubleshooting but does not show MAC address associations. show vlan brief displays VLANs configured on the switch, their status, and which ports belong to each VLAN. While this is helpful for verifying VLAN assignments, it does not indicate which devices are actively learned on the ports. show ip route shows the Layer 3 routing table and the networks the switch or router can reach, including next hops and outgoing interfaces, but it does not provide any Layer 2 MAC address information.

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

Question 146: 

Which routing protocol uses a distance-vector algorithm and has a maximum hop count of 15?

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

Answer: B

Explanation: 

RIP uses hop count as its metric and considers networks beyond 15 hops unreachable, preventing routing loops in distance-vector protocols.Routing protocols are essential for determining the best paths for data to travel across networks. Each routing protocol uses specific algorithms and metrics to evaluate paths, impacting how traffic is forwardeD) The Routing Information Protocol (RIP) is one of the earliest distance-vector routing protocols and is notable for its simplicity and reliance on hop count as its sole metriC)

RIP calculates the best path to a destination network based on the number of routers, or hops, between the source and destination. Each router that forwards a packet counts as one hop. RIP selects the route with the fewest hops as the preferred path. However, RIP imposes a limitation: it only supports a maximum of 15 hops. Any network requiring more than 15 hops is considered unreachable. This limit prevents routing loops, which are a common problem in distance-vector protocols where routers exchange routing tables periodically. RIP periodically sends its entire routing table to neighboring routers to ensure all routers have up-to-date information, but this can lead to slower convergence and temporary routing inconsistencies in larger networks.

Other routing protocols listed use different algorithms. OSPF, or Open Shortest Path First, is a link-state protocol that calculates the shortest path using metrics like cost, which can include bandwidth and delay. OSPF supports hierarchical network designs with areas to improve scalability. EIGRP, or Enhanced Interior Gateway Routing Protocol, is a hybrid protocol that combines distance-vector and link-state features and uses metrics such as bandwidth, delay, load, and reliability to determine the best path. BGP, or Border Gateway Protocol, is an exterior gateway protocol used to exchange routing information between autonomous systems on the internet. It relies on path attributes and policies rather than hop count.

In summary, RIP is the routing protocol that uses a distance-vector algorithm and limits paths to a maximum of 15 hops. While simple and easy to configure, its limitations make it suitable primarily for small networks.

The correct answer is RIP.

Question 147: 

Which command on a Cisco router displays all routes learned via OSPF?

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

Answer: A

Explanation: 

show ip route ospf displays all OSPF-learned routes in the routing table, including next hops and outgoing interfaces.

Open Shortest Path First (OSPF) is a widely used link-state routing protocol that efficiently shares routing information within an autonomous system. OSPF enables routers to calculate the shortest path to each network using the Dijkstra algorithm and maintain an up-to-date routing table. Monitoring OSPF routes is essential for network administrators to ensure proper connectivity and troubleshoot potential routing issues.

The command show ip route ospf on a Cisco router is specifically used to display all routes that have been learned through OSPF and are installed in the routing table. When executed, this command provides a detailed view of the network prefixes, the next-hop IP addresses to reach those networks, and the outgoing interfaces used to forward traffiC) This information allows administrators to verify that OSPF is operating correctly, confirm that routes are being properly advertised and received from neighboring routers, and troubleshoot routing issues if certain networks are unreachable. By using this command, it is possible to quickly identify missing or incorrect routes, which may indicate configuration problems, OSPF adjacency failures, or network topology changes.

Other commands listed serve different functions. 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. While this helps verify neighbor relationships, it does not provide information about the learned routes. show running-config shows the router’s active configuration, including OSPF network statements, interface settings, and other parameters, but it does not reflect real-time routing table entries. show ip interface brief provides a concise summary of all router interfaces, their IP addresses, and operational status, which is useful for interface verification but does not display any routing information.

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

Question 148: 

Which IPv4 address is used for automatic private IP addressing (APIPA)?

A) 10.0.0.1
B) 169.254.0.1
C) 192.168.1.1
D) 127.0.0.1

Answer: B

Explanation: 

APIPA automatically assigns an IP address in the 169.254.0.0/16 range when a host cannot contact a DHCP server.

In IPv4 networking, hosts require an IP address to communicate on a network. Typically, IP addresses are assigned manually or dynamically through a DHCP server. However, there are situations when a host cannot reach a DHCP server, such as during network outages or misconfigurations. To ensure that the host can still communicate with other devices on the same local network segment, Automatic Private IP Addressing (APIPA) is useD)

APIPA allows a host to automatically assign itself an IP address from the reserved 169.254.0.0/16 range. When a device fails to receive an IP address from a DHCP server, it selects an address in this range and verifies that it is not already in use by sending ARP requests. Once confirmed, the address is assigned to the host, enabling it to communicate with other devices using APIPA addresses on the same subnet. This mechanism ensures basic local connectivity even in the absence of a DHCP server, although APIPA addresses are not routable across different networks or the internet.

Other addresses listed serve different purposes. The address 10.0.0.1 belongs to the 10.0.0.0/8 private IP range, which is used for internal networks but requires manual configuration or DHCP assignment; it is not automatically assigned by APIPA) The address 192.168.1.1 is part of the 192.168.0.0/16 private IP range, also used for local networks and typically assigned by routers or DHCP servers, not APIPA) The address 127.0.0.1 is the loopback address, used by a host to test its own TCP/IP stack and internal network functionality; it is unrelated to automatic addressing or DHCP.

Question 149: 

Which protocol prevents ARP spoofing on untrusted ports?

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

Answer: C

Explanation: 

Dynamic ARP Inspection (DAI) validates ARP packets on untrusted ports using trusted DHCP binding information, preventing ARP spoofing attacks.

In Ethernet networks, Address Resolution Protocol (ARP) is used to map IP addresses to MAC addresses, enabling devices to communicate on a local network. However, ARP is inherently insecure because it lacks authentication, which makes it vulnerable to attacks such as ARP spoofing. In an ARP spoofing attack, a malicious device sends forged ARP messages to associate its MAC address with the IP address of another device, such as a default gateway. This can result in man-in-the-middle attacks, traffic interception, or denial of service. To mitigate this threat, Cisco switches provide the feature called Dynamic ARP Inspection (DAI).

Dynamic ARP Inspection is a security mechanism that monitors and validates ARP packets on untrusted switch ports. It relies on trusted information from the DHCP snooping binding table, which contains IP-to-MAC address mappings for devices assigned IP addresses via DHCP. When a device sends an ARP request or reply through an untrusted port, DAI checks the packet against the binding table to verify that the source IP and MAC address match the expected mapping. If the mapping is valid, the packet is allowed; if it is invalid, the packet is dropped, preventing potential ARP spoofing attacks. This ensures that only legitimate devices can send ARP responses, protecting the network from malicious manipulation of Layer 2 traffiC)

Other options listed provide different security or network functions. Port Security restricts access to a switch port based on allowed MAC addresses, controlling which devices can connect, but it does not validate ARP packets. DHCP Snooping protects the network from rogue DHCP servers by allowing only trusted DHCP servers to assign IP addresses, but it does not directly prevent ARP spoofing. STP, or Spanning Tree Protocol, prevents loops in Layer 2 networks by blocking redundant paths, but it does not address ARP-based attacks.

In summary, Dynamic ARP Inspection is the protocol specifically designed to prevent ARP spoofing by validating ARP packets on untrusted ports using trusted IP-to-MAC mappings. It is a critical security feature for maintaining the integrity of Layer 2 communications in switched networks.

Question 150: 

Which protocol is used to securely manage network devices over an IP network?

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

Answer: B

Explanation: 

SSH encrypts management traffic, providing secure remote access to network devices. Telnet, in contrast, transmits data in plaintext.

Secure management of network devices is essential to protect sensitive configuration data, passwords, and operational commands from being intercepted on the network. While multiple protocols can provide remote access to network devices, Secure Shell (SSH) is the protocol specifically designed to offer encrypted and secure management sessions over an IP network.

SSH provides a secure channel by encrypting all traffic between the management workstation and the network device. This ensures that login credentials, configuration commands, and operational data are protected from eavesdropping and man-in-the-middle attacks. When an administrator connects to a router or switch using SSH, the session is authenticated using usernames and passwords or cryptographic keys, and all subsequent communication is encrypteD) This contrasts sharply with Telnet, an older protocol for remote device management, which transmits all information in plaintext. Telnet sessions are vulnerable to interception, making it unsuitable for modern networks where security is a priority.

Other protocols listed serve different functions. FTP, or File Transfer Protocol, is used to transfer files between devices over a network. While FTP can move configuration backups or firmware images to and from network devices, it does not provide secure interactive management. Traditional FTP also transmits credentials and data in plaintext, making it insecure without encryption extensions such as FTPS or SFTP. HTTP is used to access web-based interfaces on network devices. While some network devices provide a web-based management GUI over HTTP, the standard HTTP protocol is unencrypted, exposing sensitive information. HTTPS, the secure version of HTTP, provides encryption similar to SSH but is typically used for browser-based management rather than command-line access.

In summary, SSH is the protocol specifically designed to securely manage network devices over an IP network. It provides encrypted remote access, protects credentials and configuration data, and is considered the standard for secure command-line management in modern network environments.

The correct answer is SSH.

Question 151: 

Which feature allows multiple VLANs to communicate across a single physical link?

A) Access port
B) Trunk port
C) EtherChannel
D) STP

Answer: B

Explanation: 

Trunk ports carry traffic for multiple VLANs using 802.1Q tagging, enabling inter-switch VLAN communication.

In networks with multiple VLANs, communication between switches carrying different VLAN traffic requires a mechanism to transmit multiple VLANs over a single physical link. This is accomplished through the use of trunk ports. A trunk port is a switch interface configured to carry traffic for multiple VLANs simultaneously.

Trunk ports use tagging protocols, such as IEEE 802.1Q, to identify which VLAN each frame belongs to. When a frame traverses a trunk link, the switch adds a VLAN tag to the Ethernet frame, allowing the receiving switch to determine the appropriate VLAN and forward the frame accordingly. This enables multiple VLANs to communicate across a single link between switches or between a switch and a router configured for inter-VLAN routing. Trunking is essential in larger networks with segmented VLANs, as it reduces the number of physical links required and ensures efficient utilization of network infrastructure.

Other options listed provide different functionalities. An access port is a switch port assigned to a single VLAN. It carries traffic only for that VLAN and does not use VLAN tagging, making it suitable for end devices such as computers, printers, or IP phones, but it cannot carry traffic for multiple VLANs. EtherChannel aggregates multiple physical links into a single logical link to increase bandwidth and provide redundancy, but it does not inherently carry multiple VLANs unless combined with trunking. STP, or Spanning Tree Protocol, prevents Layer 2 loops by selectively blocking redundant paths in a network. While STP is important for network stability, it does not enable VLAN traffic to traverse a single link.

In summary, trunk ports are the feature that allows a single physical link to carry traffic for multiple VLANs by tagging frames with their respective VLAN identifiers. This makes them essential for inter-switch communication in VLAN-segmented networks, optimizing link utilization while maintaining traffic separation between VLANs.

Question 152: 

Which IPv6 address is used to communicate with all nodes on a local link?

A) FF02::1
B) FF02::2
C) FE80::1
D) FF00::1

Answer: A

Explanation: 

FF02::1 is the all-nodes multicast address in IPv6, used to reach all devices on a link.

In IPv6 networks, multicast addresses are used to efficiently send a single packet to multiple devices. One of the most important multicast addresses is FF02::1, which is the all-nodes link-local multicast address. This address is used when a device needs to communicate with all nodes on the same local link, ensuring that every IPv6-enabled interface on that link receives the packet. Common use cases include network discovery, neighbor solicitation, and other protocols that require communication with all devices on a subnet without sending multiple individual packets.

The FF02::1 address is link-local, meaning that packets sent to this address are confined to the local link and are not routed beyond it. This ensures that communication is contained within the subnet and does not flood other segments of the network. Every IPv6-enabled interface automatically listens to this multicast address, allowing devices to respond to queries or participate in network protocols such as Neighbor Discovery Protocol (NDP).

Other IPv6 addresses listed serve different purposes. FF02::2 is the all-routers link-local multicast address, which targets only IPv6 routers on the local link. Devices that are not routers ignore packets sent to this address. FE80::1 is part of the link-local unicast address range, which identifies a single interface on a link for one-to-one communication. While link-local addresses are automatically assigned to interfaces, FE80::1 is used for direct communication with a specific node, not all nodes. FF00::1 is a reserved multicast address in IPv6 but is not specifically defined as the all-nodes address; it is part of the broader multicast range and may require further specification to define its scope.

Question 153: 

Which type of ACL filters traffic based only on the source IP address?

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

Answer: A

Explanation: 

Standard ACLs only filter traffic based on the source IP address, whereas extended ACLs provide more granular control including destination IP, protocol, and port.

Question 154: 

Which routing protocol is commonly used between autonomous systems on the Internet?

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

Answer: D

Explanation: 

BGP is an inter-domain routing protocol used to exchange routing information between autonomous systems on the Internet.

Routing protocols are essential for directing traffic between networks, and their use depends on the scope and scale of the network. For communication within a single autonomous system, interior gateway protocols (IGPs) such as OSPF, EIGRP, and RIP are commonly useD) However, when routing information must be exchanged between different autonomous systems (AS) on the Internet, an exterior gateway protocol (EGP) is required, and Border Gateway Protocol (BGP) is the standard choice.

BGP is designed for inter-domain routing and is widely used by Internet Service Providers (ISPs) and large organizations to exchange routing information between autonomous systems. It allows networks to advertise reachable IP prefixes and learn routes from neighboring ASes, using attributes such as AS path, next hop, and policies to determine the best path. BGP does not rely solely on metrics like hop count or bandwidth; instead, it uses policies to select routes, making it highly scalable and flexible for the complex structure of the global Internet. BGP’s design prevents routing loops between autonomous systems and allows administrators to enforce traffic routing policies based on business or performance requirements.

Other protocols listed operate differently. OSPF, or Open Shortest Path First, is a link-state interior gateway protocol used within a single AS. It calculates the shortest path using metrics like cost based on bandwidth, and is optimized for hierarchical, scalable network designs but is not intended for inter-AS routing. EIGRP, or Enhanced Interior Gateway Routing Protocol, is a Cisco-proprietary hybrid protocol used within an AS, relying on multiple metrics such as delay, bandwidth, load, and reliability to calculate routes. RIP, or Routing Information Protocol, is a distance-vector protocol that uses hop count as its metric and is suitable only for small internal networks due to its 15-hop limit. None of these protocols are designed for inter-domain routing.

In summary, BGP is the protocol specifically designed for exchanging routing information between autonomous systems on the Internet. Its ability to manage policies, scale to large networks, and prevent routing loops makes it the backbone of inter-domain Internet routing.

Question 155: 

Which command verifies the root bridge and port roles in a spanning-tree topology?

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

Answer: B

Explanation: 

show spanning-tree displays the root bridge, port roles (root, designated, blocked), and STP state, helping troubleshoot Layer 2 loops.

In Ethernet networks, loops can cause serious problems such as broadcast storms, multiple frame copies, and MAC address table instability. To prevent these issues, switches implement the Spanning Tree Protocol (STP), which detects redundant paths and selectively blocks some ports while maintaining at least one active path to ensure network connectivity. Understanding the current STP topology, including the root bridge and port roles, is essential for troubleshooting and managing Layer 2 networks effectively.

The command show spanning-tree on a Cisco switch provides a detailed view of the spanning-tree topology. It displays the identity of the root bridge, which is the switch elected to be the central reference point in the STP calculation. It also shows the roles assigned to each port, including root ports (the best path toward the root bridge), designated ports (ports responsible for forwarding traffic to a segment), and blocked ports (ports that are intentionally disabled to prevent loops). Additionally, the command reveals the state of each port, such as forwarding, learning, or blocking, as well as the STP timers and priority values. This information is invaluable for verifying that the spanning-tree configuration is working as intended and for diagnosing issues caused by misconfigurations, unexpected topology changes, or hardware failures.

Other commands listed provide different types of information but do not give the same insight into STP. show vlan brief provides a summary of VLANs on the switch, including their status and the ports assigned to each VLAN. While useful for verifying VLAN configurations, it does not display STP information or port roles. show running-config displays the active configuration of the switch, including STP settings and VLAN assignments, but it does not show real-time port roles or the current root bridge. show interfaces status lists each interface’s operational status, speed, and duplex, which is helpful for physical connectivity troubleshooting but does not provide any spanning-tree topology information.

In summary, show spanning-tree is the command that verifies the root bridge, port roles, and STP state, providing the necessary information to manage and troubleshoot Layer 2 loops effectively.

The correct answer is show spanning-tree.

Question 156: 

Which type of NAT allows multiple private IPs to share a single public IP using different port numbers?

A) Static NAT
B) Dynamic NAT
C) PAT (Port Address Translation)
D) Dual NAT

Answer: C

Explanation: 

PAT (NAT overload) allows multiple private IP addresses to use a single public IP, with unique TCP/UDP port numbers for each session.

Network Address Translation (NAT) is a technique used to map private, internal IP addresses to public IP addresses for communication over the internet. It allows organizations to conserve public IP addresses and enhance network security by hiding internal network structures. There are several types of NAT, each serving different purposes.

Port Address Translation (PAT), also known as NAT overload, is a form of dynamic NAT that allows multiple private IP addresses to share a single public IP address. PAT achieves this by assigning unique TCP or UDP port numbers to each active session. When a device on the internal network initiates a connection to an external host, the router translates the source IP and port number to the public IP address and a unique port number. The router keeps a translation table to track which internal IP and port corresponds to each external session, ensuring that return traffic is routed to the correct internal device. PAT is widely used in homes, small businesses, and enterprises to allow many devices to access the internet using a limited number of public IP addresses.

Other types of NAT function differently. Static NAT creates a one-to-one permanent mapping between a private IP address and a public IP address. It is commonly used for servers that need a fixed public IP to be reachable from the internet. Dynamic NAT maps private IP addresses to a pool of public IP addresses on a first-come, first-served basis. Unlike PAT, each private IP requires a separate public IP from the pool, which can be inefficient when there are more internal hosts than available public IPs. Dual NAT is a less commonly referenced NAT type that involves translating both source and destination IP addresses, usually in complex network scenarios, but it is not typically used for standard internet access.

In summary, PAT (Port Address Translation) is the NAT type that allows multiple private IP addresses to share a single public IP address by differentiating sessions using unique port numbers. It efficiently conserves public IP addresses while enabling multiple devices to access external networks simultaneously.

The correct answer is PAT (Port Address Translation).

Question 157: 

Which protocol is used to synchronize the clocks of network devices?

A) SNMP
B) NTP
C) DHCP
D) ICMP

Answer: B

Explanation: 

NTP ensures all devices have synchronized clocks, important for logging, authentication, and scheduled tasks.

In modern networks, accurate and synchronized time across all devices is critical for proper network operations, security, and troubleshooting. Time discrepancies can lead to problems with log correlation, authentication, and scheduled tasks, making it difficult to analyze events or detect security incidents. To address this, the Network Time Protocol (NTP) is used to synchronize the clocks of network devices.

NTP is a protocol designed to provide precise time synchronization over IP networks. It operates by having devices, known as NTP clients, query one or more NTP servers to obtain the current time. These servers can be internal devices, such as dedicated time servers, or external public NTP servers accessible over the Internet. NTP uses algorithms to account for network latency and jitter, ensuring that the client’s clock is adjusted accurately. By regularly synchronizing with reliable time sources, NTP helps maintain consistent timestamps across routers, switches, firewalls, servers, and other networked devices. This consistency is crucial for troubleshooting, as it allows network administrators to correlate events across multiple devices accurately.

Other protocols listed serve different purposes. SNMP, or Simple Network Management Protocol, is used for monitoring and managing network devices, allowing administrators to collect performance data, configure devices, and receive alerts. While SNMP provides valuable network management functions, it does not synchronize device clocks. DHCP, or Dynamic Host Configuration Protocol, automatically assigns IP addresses and other network configuration settings to hosts, including default gateways and DNS servers, but time synchronization is not part of its functionality. ICMP, or Internet Control Message Protocol, is used to report errors and operational information, such as unreachable hosts or time exceeded messages, and is commonly used in diagnostic tools like ping, but it does not synchronize clocks.

In summary, NTP is the protocol specifically designed to synchronize the clocks of network devices. By maintaining accurate and consistent time across a network, NTP ensures reliable logging, proper operation of authentication mechanisms, and the correct execution of scheduled tasks, making it an essential component of network infrastructure.

The correct answer is NTP.

Question 158: 

Which command verifies which routes were learned via EIGRP?

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

Answer: B

Explanation: 

show ip route eigrp displays all EIGRP-learned routes in the routing table along with next-hop and exit interface information.

Question 159: 

Which protocol is used to send ICMP messages like “host unreachable” or “TTL exceeded”?

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

Answer: B

Explanation: 

ICMP communicates errors and operational messages for IP networks, including unreachable hosts, network congestion, and testing connectivity (ping).

Question 160: 

Which feature prevents loops on a Layer 2 network while allowing redundant paths?

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

Answer: C

Explanation: 

STP (Spanning Tree Protocol) detects loops and places redundant paths in a blocked state while maintaining at least one active path to prevent broadcast storms.

In Ethernet networks, loops at Layer 2 can cause serious issues such as broadcast storms, multiple frame copies, and MAC address table instability. These problems arise when redundant paths exist between switches, which are common in networks designed for fault tolerance and high availability. To manage these redundant paths without causing network disruption, the Spanning Tree Protocol (STP) is used.

STP is a Layer 2 protocol that detects loops in a network and selectively blocks some of the redundant paths while ensuring that at least one active path remains available for communication. The protocol elects a root bridge, which serves as the reference point for all path calculations. STP assigns roles to switch ports, such as root ports, designated ports, and blocked ports, based on their location relative to the root bridge and their path cost. By doing so, it prevents loops from forming while allowing redundant links to exist for failover purposes. If the active path fails, STP recalculates the topology and activates a previously blocked port to maintain network connectivity. This process ensures both stability and redundancy in Layer 2 networks.

Other protocols listed perform different functions. RIP, or Routing Information Protocol, is a distance-vector routing protocol that operates at Layer 3 to determine the best path to a destination network using hop count. It does not prevent Layer 2 loops. OSPF, or Open Shortest Path First, is a link-state routing protocol that also functions at Layer 3, calculating the shortest path within an autonomous system based on metrics like cost, but it does not handle Layer 2 loops. HSRP, or Hot Standby Router Protocol, provides high availability for default gateway IP addresses by allowing multiple routers to share a virtual IP, but it does not manage loops on a Layer 2 network.

In summary, STP is the feature that prevents loops on a Layer 2 network while allowing redundant paths. By blocking unnecessary links and maintaining a loop-free topology, STP ensures network stability, prevents broadcast storms, and provides redundancy for high availability.

The correct answer is STP.