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Question 46:
Which protocol provides loop-free path selection in a switched LAN environment?
A) STP
B) OSPF
C) EIGRP
D) RIP
Answer:
A)
Explanation:
The correct answer is STP (Spanning Tree Protocol) (A), which is specifically designed to provide a loop-free topology in a Layer 2 switched LAN environment. In Ethernet networks that utilize switches, redundant links are often implemented to provide network resiliency and prevent a single point of failure. However, these redundant paths can create broadcast storms, multiple frame copies, and MAC table instability if loops occur. STP is the protocol that prevents these Layer 2 loops by dynamically identifying a loop-free topology and blocking redundant paths while keeping them available as backups in case the primary path fails.
STP operates by electing a single switch as the root bridge, which serves as the reference point for all path calculations. Each switch in the network then calculates the shortest path to the root bridge using the Bridge Protocol Data Units (BPDUs), which are exchanged regularly among switches. Based on these calculations, STP determines which ports should remain in the forwarding state and which should be placed in a blocking state to prevent loops. This ensures that there is only one active path between any two devices in the Layer 2 network at any given time, effectively eliminating the risk of switching loops.
Other options listed in the question are routing protocols, not loop-prevention mechanisms at the Layer 2 level. OSPF (B) and EIGRP (C) are dynamic Layer 3 routing protocols used for IP route determination in routed networks. OSPF uses link-state information to calculate the shortest path first (SPF) and update routing tables, while EIGRP uses a hybrid distance-vector algorithm. Both operate at Layer 3 and have no direct role in preventing Layer 2 switching loops. Similarly, RIP (D) is a distance-vector routing protocol that uses hop count as its metric for routing decisions. Like OSPF and EIGRP, RIP functions at Layer 3 and does not address Layer 2 loop prevention.
Implementing STP correctly involves understanding its timers, port roles, and states. The five port states—Blocking, Listening, Learning, Forwarding, and Disabled—allow switches to process BPDUs, learn MAC addresses, and eventually forward traffic without creating loops. Administrators can also optimize STP using variations like Rapid Spanning Tree Protocol (RSTP) or Multiple Spanning Tree Protocol (MSTP) to improve convergence times and support VLANs. RSTP significantly reduces the time it takes for the network to recover from a topology change, while MSTP allows multiple VLANs to share a common spanning tree, improving scalability and efficiency.
STP is essential in enterprise LAN environments with redundant connections, as loops can severely degrade network performance, causing high CPU utilization on switches and dropped traffic. Without STP, a single network loop can result in broadcast storms, where Ethernet frames continuously circulate, leading to network-wide congestion and service outages.
Question 47:
Which IP addressing type allows communication within a single link only?
A) Link-local
B) Global unicast
C) Unique local
D) Multicast
Answer:
A)
Explanation:
The correct answer is Link-local (A). Link-local addresses are a type of IP address that are automatically configured on interfaces and are valid only within a single network link or segment. In IPv6, link-local addresses typically begin with the prefix FE80::/10, while in IPv4, the equivalent is 169.254.0.0/16, which is used when a device cannot obtain an IP address from a DHCP server. These addresses are crucial for local communication between devices on the same physical or logical segment without requiring a globally routable address.
Link-local addresses are primarily used for network operations that must occur before any global or site-local addressing is available. For example, in IPv6, they are required for the functioning of essential protocols such as Neighbor Discovery Protocol (NDP), which replaces ARP in IPv6. NDP uses link-local addresses to resolve the MAC addresses of neighboring devices, determine link-layer addresses, and ensure that nodes can communicate directly on the local link. Additionally, routing protocols like OSPFv3 or EIGRP for IPv6 rely on link-local addresses for exchanging routing information between routers on the same link. This ensures that routers can establish adjacency and communicate routing updates without needing a global IPv6 address.
Other types of IP addresses listed in the options serve different purposes. Global unicast (B) addresses are routable on the public internet and can communicate across multiple links or networks. They are assigned by ISPs or internal addressing schemes and must be unique globally. Using a global unicast address for local-link communication is unnecessary and inefficient, as link-local addresses suffice for on-link interactions. Unique local addresses (C) are intended for private networks, similar to IPv4 private address ranges (like 10.0.0.0/8, 192.168.0.0/16), and can communicate across multiple links within an organization but are not intended for global internet routing. These addresses provide isolation and security for internal communication but are not limited to a single link. Multicast (D) addresses are used for one-to-many communication, allowing a single device to send traffic to multiple recipients subscribed to a specific multicast group. While multicast can operate on a local link, it is not inherently restricted to a single link and can be routed across multiple networks if configured appropriately.
Link-local addresses are automatically assigned and do not require manual configuration. They ensure that devices can communicate immediately after interface initialization, which is particularly useful in environments where DHCP is unavailable or not yet configured. They are also essential in network troubleshooting, as administrators can use link-local addresses to test connectivity and verify local network configurations without relying on higher-level addressing.
Security considerations for link-local addresses involve the fact that they are limited to the local segment, meaning that traffic cannot traverse routers. This provides a level of containment, making link-local addresses less susceptible to external attacks. However, administrators must still manage access controls and firewall rules at the interface level to prevent unauthorized local access.
Question 48:
Which command shows which MAC addresses are associated with which switch ports?
A) show mac address-table
B) show ip route
C) show interfaces
D) show vlan brief
Answer:
A)
Explanation:
The show mac address-table command displays all MAC addresses learned by a switch along with the corresponding interface and VLAN. Switches use this table to forward traffic efficiently, avoiding unnecessary flooding. MAC addresses age out if unused to maintain table accuracy.
Other commands serve different functions. Show ip route displays Layer 3 routing information, show interfaces displays interface status, and show vlan brief displays VLAN configuration but not MAC address associations.
CCNA candidates should understand how MAC tables interact with VLANs and STP. Troubleshooting connectivity issues often involves verifying the correct mapping of MAC addresses to physical ports, identifying loops, or addressing flooding issues caused by incorrect or missing entries.
Question 49:
Which technology allows multiple physical switches to be managed as a single device?
A) StackWise
B) EtherChannel
C) VLAN
D) STP
Answer:
A)
Explanation:
StackWise allows multiple physical Cisco switches to operate as a single logical switch with one management IP address. Stack members synchronize configurations, MAC address tables, and control plane information, simplifying administration and improving redundancy.
EtherChannel aggregates links for bandwidth but does not unify switches as a single management entity. VLANs segment traffic logically, and STP prevents loops but does not unify switch management.
Understanding StackWise is critical for CCNA candidates designing enterprise LANs. Key concepts include stack member roles (master and members), stack priority, failover handling, and interaction with VLANs and STP for high-availability deployments.
Question 50:
Which command displays the current routing protocol in use on a router?
A) show ip protocols
B) show ip route
C) show running-config
D) show interfaces
Answer:
A)
Explanation:
The command show ip protocols (A) is a critical tool on Cisco routers used to display information about the dynamic routing protocols currently configured and running on the device. This command provides detailed insight into which routing protocols are active, their configuration parameters, timers, networks being advertised, and other protocol-specific information, making it invaluable for network administrators when troubleshooting, verifying, or optimizing routing operations.
When executed, show ip protocols lists the routing protocols that the router is participating in, such as OSPF, EIGRP, RIP, or BGP. It shows the networks that are being advertised by the router under each protocol, the routing protocol timers (such as update intervals for RIP or hello and dead intervals for OSPF), administrative distance values, and information about neighboring routers. This output allows administrators to quickly verify that the intended routing protocol is active and configured correctly across the network. For example, if a network engineer expects OSPF to operate on certain interfaces, running this command confirms that OSPF is indeed enabled and includes the correct networks in its area. It also helps in identifying misconfigurations, such as missing network statements or incorrect timers that may cause routing inconsistencies or slow convergence.
Other options provided in the question, while related to routing and network information, serve different purposes. Show ip route (B) displays the current routing table of the router, including routes learned via static configuration, directly connected interfaces, or dynamic routing protocols. While this command shows which routes are in use, it does not explicitly indicate which routing protocols are responsible for those routes or provide configuration parameters of the protocols themselves. It is useful for verifying routing paths but lacks the detailed protocol-level information that show ip protocols provides. Show running-config (C) displays the entire active configuration of the router, including interface settings, routing protocol configurations, access control lists, and other parameters. While the running configuration contains information about configured routing protocols, extracting protocol details requires manually parsing through the output, making it less efficient for quick verification or troubleshooting. Show interfaces (D) displays status and statistics for the router interfaces, such as interface operational state, IP addresses, and packet counters. This command does not provide any direct information about which routing protocols are running or how they are configured.
The show ip protocols command is particularly useful in network troubleshooting scenarios. For instance, if routers are not exchanging routes as expected, administrators can use this command to ensure that the correct protocols are configured, the appropriate networks are being advertised, and the timers align with the rest of the network configuration. It is also helpful in auditing and documentation, as it provides a clear view of active dynamic routing protocols without sifting through the complete running configuration.
Additionally, this command provides a snapshot of protocol behavior in real-time, allowing engineers to verify that the router is participating correctly in protocol-specific functions such as neighbor discovery, route advertisement, and convergence. It also supports the assessment of administrative distances, which is critical when multiple protocols are used simultaneously on the same device.
Question 51:
Which VLAN type allows multiple VLANs to pass traffic between switches?
A) Trunk VLAN
B) Access VLAN
C) Management VLAN
D) Voice VLAN
Answer:
A)
Explanation:
Trunk VLANs carry multiple VLANs over a single physical link, using tagging protocols such as IEEE 802.1Q to differentiate traffic. Trunking allows Layer 2 segmentation across multiple switches while maintaining VLAN separation.
Access VLANs assign a single VLAN per port, management VLANs provide administrative access, and voice VLANs prioritize VoIP traffic.
CCNA candidates must know trunk configuration, verification commands, and native VLAN settings to prevent VLAN mismatches or connectivity issues between switches in enterprise networks.
Question 52:
Which command displays interface IP addresses and operational status?
A) show ip interface brief
B) show running-config
C) show vlan brief
D) show mac address-table
Answer:
A)
Explanation:
The command show ip interface brief (A) is an essential diagnostic tool used on Cisco routers and switches to quickly display the operational status and IP configuration of all interfaces on the device. This command provides a summarized view, making it highly valuable for network administrators when troubleshooting, monitoring, or verifying network configurations.
When executed, show ip interface brief outputs several key pieces of information, including the interface name, IP address assigned, interface status (administratively up or down), and line protocol status (up or down). The administrative status indicates whether the interface is enabled or disabled by configuration, while the line protocol status shows if the interface is operational and able to forward traffic. This allows network engineers to rapidly identify misconfigurations, disabled interfaces, or connectivity problems. For example, an interface might be administratively up but operationally down due to a cabling issue, mismatch in duplex settings, or a problem with the connected device. The command therefore provides immediate insight into such discrepancies without needing to delve into detailed configuration files.
Other options listed in the question serve different purposes and do not provide the same summarized operational view. Show running-config (B) displays the entire current configuration of the device, including interface configurations, routing protocols, VLAN assignments, and other device settings. While it contains IP addresses and interface configurations, it does not provide a quick operational status overview, making it less efficient for troubleshooting real-time connectivity issues. Show vlan brief (C) focuses on VLANs configured on the switch, listing VLAN IDs, names, status, and assigned ports. Although this command is helpful for verifying VLAN membership and operation, it does not display IP addresses or the up/down status of interfaces. Show mac address-table (D) displays the MAC address table of a switch, mapping MAC addresses to specific interfaces. This is valuable for identifying where devices are located within the network at Layer 2 but provides no IP-level information or operational status of the interfaces.
Using show ip interface brief is particularly important in scenarios such as initial device configuration, troubleshooting routing or switching issues, and verifying network connectivity after changes. For instance, when configuring inter-VLAN routing on a router or Layer 3 switch, administrators can use this command to confirm that each interface has the correct IP address and is operational before testing connectivity with ping or traceroute commands. It is also commonly used in network documentation and audits to provide a snapshot of interface states and IP assignments.
The command is lightweight, executes quickly, and is supported across most Cisco IOS devices, making it a standard part of the toolkit for daily network operations. Additionally, it can be combined with other commands or filtered with keywords to focus on specific interfaces, enhancing its utility for large-scale networks.
Question 53:
Which routing protocol uses hop count as its metric?
A) RIP
B) OSPF
C) EIGRP
D) BGP
Answer:
A)
Explanation:
RIP (Routing Information Protocol) is a distance-vector protocol that uses hop count to determine the best path to a destination network. The maximum allowable hop count is 15, with 16 considered unreachable. RIP sends periodic updates to maintain route information and is classless when using RIPv2.
OSPF uses link-state metrics based on cost, EIGRP uses bandwidth and delay metrics, and BGP is a path-vector protocol using attributes like AS path and policy-based rules.
CCNA candidates must understand RIP’s characteristics, limitations, configuration commands, and verification procedures to troubleshoot routing in smaller or lab networks.
Question 54:
Which protocol translates private IP addresses to public IP addresses?
A) NAT
B) ARP
C) ICMP
D) DHCP
Answer:
A)
Explanation:
The correct answer is NAT (A). Network Address Translation (NAT) is a protocol and a networking technique used to map private IP addresses within an internal network to a public IP address for communication over the internet. This mechanism allows multiple devices on a private network to share a single public IP address, which is crucial because IPv4 addresses are limited and not every device can have a globally unique address. NAT operates at the network layer (Layer 3) of the OSI model and is commonly implemented on routers and firewalls to facilitate secure and efficient routing of traffic between private and public networks.
NAT works by modifying the source or destination IP address of IP packets as they pass through a router or NAT-enabled device. For outbound traffic, the private IP address of a host is replaced with the public IP address of the NAT device, and a unique port number may be added if Port Address Translation (PAT) is used, allowing multiple internal devices to share a single public IP. When the response traffic returns from the internet, the NAT device reverses the translation, ensuring that the packet is delivered to the correct internal host. This functionality not only conserves public IP addresses but also adds a layer of security by hiding internal network structure from external networks.
Other protocols listed in the options perform different network functions. ARP (B), or Address Resolution Protocol, operates at Layer 2 and Layer 3, translating IP addresses to MAC addresses within a local network segment. ARP is essential for local communication on a LAN but does not provide IP address translation for external communication. ICMP (C), Internet Control Message Protocol, is used primarily for network diagnostics and error reporting. For example, ping and traceroute use ICMP messages to test connectivity and measure response times, but ICMP does not handle address translation. DHCP (D), Dynamic Host Configuration Protocol, is responsible for automatically assigning IP addresses, subnet masks, default gateways, and other network configuration parameters to hosts on a network. While DHCP provides IP addressing within a network, it does not translate addresses for internet access.
NAT can be implemented in various forms depending on network requirements. Static NAT maps a single private IP address to a single public IP address, which is often used for servers that must be accessible from the internet. Dynamic NAT assigns a private IP to a public IP from a pool of available addresses, supporting multiple hosts but limited by the number of public addresses. PAT, often referred to as NAT overload, allows multiple private IPs to share a single public IP using unique port numbers, which is the most common form in home and enterprise networks.
The advantages of NAT extend beyond IP conservation. It provides a level of security by obscuring internal addresses from external networks, reducing direct exposure to potential attacks. However, NAT can complicate certain applications that embed IP addresses in the payload or require inbound connections, such as some VoIP or peer-to-peer applications. In such cases, techniques like NAT traversal or configuring port forwarding are necessary.
Question 55:
Which IPv4 address is reserved for loopback testing?
A) 127.0.0.1
B) 192.168.1.1
C) 10.0.0.1
D) 169.254.1.1
Answer:
A)
Explanation:
In IPv4 networking, the concept of a loopback address is fundamental for testing and troubleshooting network configurations without sending packets onto a physical network. The question asks which IPv4 address is reserved for loopback testing, and the correct answer is 127.0.0.1 (A). The loopback address is a special, reserved IP address used to test the functionality of the TCP/IP stack on a host device locally. When a packet is sent to this address, it is routed internally by the operating system back to the source host, allowing administrators and network engineers to verify that the network software and protocols on the device are operating correctly.
Using 127.0.0.1 enables testing without any dependency on external network connectivity, making it an essential tool for isolating software or configuration issues. For example, if a service such as a web server or database server is installed on a host, administrators can ping 127.0.0.1 to ensure the network stack is functioning before attempting to communicate with other devices on the network. This helps quickly differentiate between local configuration problems and external connectivity issues.
Other options listed in the question serve different purposes. 192.168.1.1 (B) is a private IP address commonly used as the default gateway in local area networks, particularly for home or small business routers. It is not reserved for testing and is intended for communication between hosts within a private network. 10.0.0.1 (C) is another private IP address from the Class A private address space, used in larger private networks. Like 192.168.1.1, it facilitates communication among hosts in the local network but does not provide loopback functionality. 169.254.1.1 (D) is an Automatic Private IP Addressing (APIPA) address. Windows devices assign these addresses automatically when a DHCP server is unavailable, allowing limited communication with other hosts in the same subnet, but it is not used for loopback or testing the local TCP/IP stack.
The IPv4 loopback range is defined as 127.0.0.0 to 127.255.255.255, with 127.0.0.1 being the most commonly used address. Network engineers often use the ping command with this address (ping 127.0.0.1) to test connectivity and verify that TCP/IP is installed and functioning correctly. Other loopback addresses in the range can also be used for similar testing purposes, but 127.0.0.1 is the de facto standard for most operating systems and network utilities.
Loopback testing is also essential for application development. Developers can run services locally on their machines and use the loopback address to simulate network interactions without deploying applications to external networks. This improves efficiency, prevents unnecessary network traffic, and provides a secure testing environment. Additionally, troubleshooting tools such as netstat, telnet, or curl often use the loopback interface to diagnose service availability or socket-level issues on the local host.
Question 56:
Which command verifies the routing table entries on a Cisco router?
A) show ip route
B) show interfaces
C) show vlan brief
D) show mac address-table
Answer:
A)
Explanation:
The correct answer is show ip route, which is a fundamental command used on Cisco routers to display the contents of the routing table. The routing table is a critical component of a router, as it contains information about all known networks, including directly connected networks, static routes, and dynamically learned routes from routing protocols such as OSPF, EIGRP, and BGP. By using show ip route, administrators can verify that the router knows how to reach different networks and identify the source and type of each route.
When the show ip route command is executed, the output provides several important pieces of information. It displays network prefixes, subnet masks, and the next-hop IP addresses that packets should be forwarded to reach a destination. It also indicates the route type, showing whether it is directly connected (C), static (S), or dynamically learned through a specific routing protocol, such as OSPF (O), EIGRP (D), or BGP (B). This helps network administrators understand the origin of each route and troubleshoot routing issues effectively.
The routing table also provides administrative distance values and metrics associated with each route, which routers use to select the best path to a destination when multiple routes exist. By examining the routing table through show ip route, administrators can ensure that optimal paths are selected, redundant paths are recognized, and misconfigurations or missing routes are identified. For example, if a network is unreachable, the administrator can check the routing table to confirm whether a route exists and whether it points to the correct next-hop device.
Other commands listed do not provide the same routing-specific information. The show interfaces command displays the status, IP addresses, and statistics of router interfaces, which is useful for checking interface health but does not reveal routing paths. Show vlan brief lists VLAN information and associated ports on a switch, providing Layer 2 visibility but no Layer 3 routing information. Show mac address-table displays the learned MAC addresses on a switch port, which is essential for Layer 2 troubleshooting but does not indicate routing paths between networks.
The show ip route command is also critical in verifying the correct operation of dynamic routing protocols. After configuring OSPF, EIGRP, or BGP, administrators use show ip route to ensure that learned routes are correctly installed in the routing table. It can also help in validating redistribution between routing protocols, checking for routing loops, and confirming proper failover in redundant network designs.
Question 57:
Which IPv6 address type is used for one-to-many communication?
A) Multicast
B) Unicast
C) Anycast
D) Link-local
Answer:
A)
Explanation:
In IPv6 networking, understanding the different address types is crucial for designing, configuring, and troubleshooting networks effectively. The question asks which IPv6 address type is used for one-to-many communication. The correct answer is Multicast (A), as multicast addresses are specifically designed to send packets from a single source to multiple destinations simultaneously.
Multicast is a communication method that allows one device to send data to a group of devices without broadcasting to the entire network. This is highly efficient for applications such as streaming video, online conferencing, or any service that needs to deliver identical content to multiple receivers. Unlike broadcast in IPv4, which sends packets to all nodes in a subnet, multicast in IPv6 targets only the members of a specific multicast group, reducing unnecessary traffic and conserving bandwidth.
IPv6 has a dedicated range of multicast addresses, which start with the prefix FF00::/8. These addresses are used to identify groups of interfaces that should receive specific traffic. Multicast addresses include scope information that defines the range of delivery, such as link-local, site-local, or global scope. For instance, a link-local multicast address (FF02::/16) targets devices within the same link or subnet, ensuring efficient communication without reaching unintended nodes outside the local network.
In contrast, Unicast addresses (B) represent a one-to-one communication model. When a device sends a packet to a unicast address, it is delivered to a single interface, making it suitable for standard host-to-host communication but not for one-to-many scenarios. Anycast addresses (C) in IPv6 are assigned to multiple interfaces, but the traffic is routed to the nearest interface based on the routing protocol. Anycast is primarily used for load balancing or directing traffic to the closest server, rather than distributing it to multiple recipients simultaneously. Link-local addresses (D) are used for communication between nodes on the same link, typically for routing protocols or network management purposes, but they do not provide one-to-many communication by default.
In practical network operations, multicast is used extensively for efficient communication. Common examples include the Neighbor Discovery Protocol (NDP) in IPv6, which relies on multicast for address resolution and network discovery. Multicast also enables services like IPv6 streaming applications, routing updates from protocols such as OSPFv3, and certain DNS services. By using multicast, network administrators can reduce network congestion compared to sending multiple unicast packets or broadcasting to all devices.
Implementing IPv6 multicast requires understanding multicast group membership, managed using protocols such as MLD (Multicast Listener Discovery), which allows nodes to join or leave multicast groups dynamically. Proper configuration and monitoring ensure that multicast traffic is delivered only to interested nodes, maintaining efficiency and minimizing unnecessary data flow.
Question 58:
Which command provides detailed STP information including root bridge ID and port roles?
A) show spanning-tree detail
B) show ip route
C) show vlan brief
D) show mac address-table
Answer:
A)
Explanation:
The command “show spanning-tree detail” is an essential diagnostic and verification tool for network administrators working with Cisco switches. Spanning Tree Protocol (STP) is a Layer 2 protocol that prevents loops in Ethernet networks by creating a loop-free logical topology. When multiple switches are connected in a network, loops can occur, which may lead to broadcast storms, multiple frame copies, and MAC table instability. STP ensures that there is only one active path between any two network devices, dynamically blocking redundant paths and allowing them to become active if the primary path fails.
Using “show spanning-tree detail” provides comprehensive information about the STP configuration and the current state of the spanning tree on a switch. The command output includes the root bridge ID, root path cost, bridge priority, timers, and port roles for each VLAN. The root bridge is the logical center of the spanning tree topology, and knowing its identity is critical because all switches in the network calculate their path cost to the root bridge to determine which ports should be forwarding and which should be blocking. By examining the root bridge ID and priority, administrators can ensure that the desired switch is acting as the root bridge and make adjustments if necessary.
The command also shows port roles such as root port, designated port, and blocked ports. The root port is the port on a non-root switch with the lowest path cost toward the root bridge. The designated port is responsible for forwarding traffic toward downstream devices on a segment. Blocked ports prevent loops but remain in a listening/learning state, ready to transition to a forwarding state if the network topology changes. This information is vital for troubleshooting network issues related to loops or misconfigured STP priorities.
Another important aspect displayed by the command is the STP timers, including hello time, forward delay, and max age, which affect how quickly the spanning tree responds to topology changes. Monitoring these timers helps administrators tune the network for convergence speed and stability. Detailed STP output may also include information about BPDU transmissions, port costs, and interface status, which are all valuable for in-depth troubleshooting of Layer 2 network behavior.
Other commands like “show ip route” provide Layer 3 routing information but do not give insight into Layer 2 loop prevention mechanisms. “Show vlan brief” displays VLAN configuration and port assignments but does not indicate how traffic flows are managed at Layer 2. “Show mac address-table” lists learned MAC addresses but does not provide topology or loop prevention details. Therefore, “show spanning-tree detail” is the most appropriate command for detailed STP information and analysis.
For CCNA-level network administration, understanding and interpreting the output of “show spanning-tree detail” is crucial. It allows administrators to verify that the network topology is loop-free, identify misconfigurations, and troubleshoot issues such as unexpected blocked ports or slow convergence after topology changes. Regularly monitoring STP using this command ensures that the network maintains redundancy without introducing loops, providing stable and reliable Layer 2 connectivity.
Question 59:
Which protocol replaces ARP in IPv6 networks?
A) NDP
B) ICMPv4
C) DHCPv6
D) RARP
Answer:
A)
Explanation:
The correct answer is NDP, which stands for Neighbor Discovery Protocol. NDP is a fundamental protocol in IPv6 networks that replaces the functionality of ARP (Address Resolution Protocol) used in IPv4. In IPv4, ARP maps IP addresses to MAC addresses so that data can be delivered to the correct device on a local network. IPv6, however, does not use ARP; instead, it relies on NDP to perform address resolution, along with several other essential functions, including router discovery, address autoconfiguration, and duplicate address detection.
NDP operates using ICMPv6 messages rather than broadcasts, which improves efficiency and security. IPv6 nodes use NDP to discover other devices on the same link, determine their link-layer addresses, find routers, and maintain reachability information. The key NDP message types include Neighbor Solicitation (NS), Neighbor Advertisement (NA), Router Solicitation (RS), and Router Advertisement (RA). For address resolution, a host sends a Neighbor Solicitation message asking, “Who has this IPv6 address?” The target node responds with a Neighbor Advertisement message, providing its MAC address. This process replaces the broadcast-based ARP mechanism in IPv4, reducing unnecessary network traffic and improving performance on large networks.
Another important feature of NDP is its integration with IPv6 stateless address autoconfiguration (SLAAC). Hosts can automatically configure their IPv6 addresses based on information received from router advertisements. NDP also ensures that no duplicate addresses exist on a link by performing duplicate address detection (DAD) before assigning an address to an interface. These capabilities make NDP a multifunctional protocol that combines several roles in IPv6 networking, unlike ARP, which only resolves addresses.
Other options listed are incorrect because they serve different purposes. ICMPv4 is used in IPv4 networks for error reporting and diagnostics, such as ping and traceroute, and does not provide address resolution. DHCPv6 is used to assign IPv6 addresses and configuration information to hosts but is not directly responsible for resolving IP-to-MAC addresses. RARP (Reverse Address Resolution Protocol) is an obsolete protocol that maps MAC addresses to IP addresses in legacy IPv4 systems and is not used in IPv6.
Using NDP improves network efficiency and reduces the security risks associated with broadcast-based protocols. IPv6 networks benefit from neighbor discovery because it allows devices to communicate directly with relevant peers without flooding the network. The use of ICMPv6 messages for NDP also allows for better integration with security mechanisms such as Secure Neighbor Discovery (SEND), which provides cryptographic verification to prevent address spoofing and man-in-the-middle attacks.
Question 60:
Which command shows which interfaces are up and their IP addresses?
A) show ip interface brief
B) show running-config
C) show vlan brief
D) show mac address-table
Answer:
A)
Explanation:
The command “show ip interface brief” is a fundamental tool used by network administrators to quickly verify the status and configuration of interfaces on Cisco routers and switches. It provides a concise summary of all interfaces, their IP addresses, and their operational status, making it essential for troubleshooting and network verification. The command displays key information such as the interface name, IP address assigned to the interface, and the status of the interface from both the hardware perspective (line protocol) and operational perspective (administrative status).
When a network administrator executes “show ip interface brief,” the output lists each interface along with its IP address, method of assignment (manual or DHCP), and the interface’s status (up or down). The “Status” column indicates whether the interface is physically active, while the “Protocol” column shows whether the Layer 2/3 protocol is operational. For instance, an interface may show “administratively up” but “protocol down” if there is no connectivity at Layer 2, which helps isolate network issues such as cabling problems, misconfigured duplex settings, or VLAN mismatches. This clear distinction between administrative status and operational protocol status allows administrators to quickly determine whether an interface is simply administratively disabled or if it is facing a connectivity issue.
The command is especially useful in troubleshooting scenarios where devices are not communicating correctly. By checking which interfaces are up and which are down, administrators can identify problem areas in the network without needing to examine each interface individually through more detailed commands. Additionally, seeing IP addresses in the same output allows verification that the correct addressing is configured and helps confirm whether IP routing can occur across interfaces. This is vital for ensuring devices are reachable within the network and for confirming that routing protocols have the correct interface information for proper operation.
Other commands like “show running-config” provide more detailed configuration information but require more effort to parse through and do not provide a concise operational status. “Show vlan brief” is useful for verifying VLAN assignments on switches but does not provide IP address information. “Show mac address-table” is used for checking Layer 2 MAC address learning and is not relevant for checking IP addresses or interface statuses. Therefore, “show ip interface brief” stands out as the most efficient and effective command for a quick operational overview of interface health and configuration.
Network administrators rely heavily on this command for routine checks, especially after deploying new interfaces, modifying configurations, or troubleshooting connectivity issues. It is also instrumental in preparing documentation, verifying network changes, and ensuring that interfaces are correctly assigned to the intended networks. For CCNA-level knowledge, mastering this command is critical because it forms the foundation for network verification, troubleshooting, and understanding the relationship between Layer 2 and Layer 3 connectivity.