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Question 91:
Which protocol enables secure remote access to a Cisco device?
A) SSH
B) Telnet
C) HTTP
D) FTP
Answer:
A)
Explanation:
The correct answer is A) SSH. Secure Shell (SSH) is a network protocol that provides secure, encrypted communication between a client and a network device, such as a Cisco router or switch. SSH allows administrators to perform remote configuration, monitoring, and troubleshooting tasks while ensuring that all transmitted data, including usernames, passwords, and commands, is encrypted. This security feature is crucial in modern networks where sensitive information must be protected from eavesdropping and unauthorized access.
SSH operates at the application layer and uses public key cryptography to authenticate the connecting client and server. This ensures that both parties are who they claim to be before any sensitive data is exchanged. SSH also encrypts all traffic between the client and device, making it resistant to interception, man-in-the-middle attacks, and packet sniffing, which are common vulnerabilities in plain-text protocols.
Option B, Telnet, is an older protocol that provides remote access to network devices. While it functions similarly to SSH in terms of command-line management, it transmits data in clear text, including login credentials. This lack of encryption makes Telnet insecure for use in modern networks, especially when accessing devices over the internet or untrusted networks. As a result, network best practices recommend replacing Telnet with SSH whenever possible.
Option C, HTTP, is a protocol used primarily for web traffic. While some Cisco devices provide a web-based management interface accessible through HTTP, this protocol does not inherently provide encryption. HTTP traffic, including login credentials, can be intercepted by attackers. The secure variant, HTTPS, does encrypt web-based management traffic, but for command-line access to a device, SSH remains the preferred protocol.
Option D, FTP, is used for transferring files between devices but does not provide secure remote device access. Traditional FTP transmits credentials and data in plain text, making it unsuitable for secure administrative access. SFTP, which operates over SSH, does provide secure file transfer, but it is not a management protocol for device configuration.
Implementing SSH on Cisco devices involves enabling the SSH server, configuring domain names, generating encryption keys, and creating user accounts with strong passwords. Administrators often set the transport input to SSH on vty (virtual terminal) lines to restrict remote access to encrypted connections only. This configuration ensures that even if an attacker gains access to the network, they cannot intercept login credentials or administrative commands.
SSH also supports advanced security features such as key-based authentication, which replaces passwords with cryptographic keys for enhanced security, and access control lists to restrict which hosts can initiate SSH connections. By using SSH, administrators can securely manage routers, switches, and other network devices while maintaining compliance with security policies and best practices.
Question 92:
Which IPv6 address type is used for communication within a single subnet?
A) Link-local
B) Global unicast
C) Unique local
D) Multicast
Answer:
A)
Explanation:
Link-local IPv6 addresses are automatically assigned to every IPv6-enabled interface and are used for communication within the same subnet or link. The address range for link-local addresses is fe80::/10. These addresses are critical for fundamental IPv6 operations such as Neighbor Discovery Protocol (NDP), which replaces ARP in IPv4 networks. NDP relies on link-local addresses to discover other devices on the same subnet, resolve IPv6 addresses to MAC addresses, and detect duplicate addresses.
Link-local addresses are also used for essential communication between routers and hosts for functions like Router Solicitation (RS) and Router Advertisement (RA), which are part of the Stateless Address Autoconfiguration (SLAAC) process. SLAAC allows devices to automatically configure global unicast addresses while still relying on link-local addresses for initial network discovery and communication with the local router.
Unlike global unicast addresses, which are routable across the internet, link-local addresses cannot traverse routers and are confined to a single link. Unique local addresses (ULAs) are intended for private networks similar to RFC 1918 IPv4 ranges and can be routed internally but are not globally reachable. Multicast addresses enable one-to-many communication but serve different purposes than link-local addresses.
For CCNA candidates, it is essential to understand the operational role of link-local addresses, how they are automatically generated based on the interface MAC address (with options for privacy extensions), and how they interact with routing protocols like OSPFv3 and EIGRP for IPv6. Troubleshooting often involves verifying link-local addresses with commands such as show ipv6 interface brief, understanding neighbor tables, and diagnosing issues like address conflicts or misconfigured interfaces.
Additionally, candidates should understand that link-local addresses are mandatory in IPv6 and are always assigned to an interface, even if no global or unique local addresses are configured. This concept underpins IPv6 routing and ensures that basic communication is always possible at the link layer, providing a foundation for more advanced IPv6 operations and security considerations.
Question 93:
Which command verifies OSPF neighbor relationships?
A) show ip ospf neighbor
B) show ip route
C) show running-config
D) show interfaces
Answer:
A)
Explanation:
The show ip ospf neighbor command is a critical diagnostic tool in OSPF networks. OSPF is a link-state routing protocol, and proper operation requires routers to form adjacencies with their neighbors. This command displays information such as the router IDs of neighbors, neighbor states (Down, Init, 2-Way, Full), interface priority, and the amount of time since the last Hello packet was received. Understanding neighbor states is essential for verifying OSPF operation and diagnosing connectivity or configuration issues.
The OSPF neighbor establishment process starts with sending Hello packets. Routers check for matching OSPF parameters such as Hello/Dead intervals, area IDs, and authentication types. A neighbor that fails to meet these requirements will not transition to the Full state, preventing the exchange of Link-State Advertisements (LSAs) and potentially disrupting network topology.
LSAs contain information about each router’s interfaces and network segments, allowing OSPF routers to construct a complete map of the network and calculate optimal paths using the Shortest Path First (SPF) algorithm. Without fully formed adjacencies, the routing tables may be incomplete or inconsistent, leading to potential routing loops or black holes.
CCNA candidates should be able to interpret the output of show ip ospf neighbor, identify misconfigured interfaces, verify OSPF timers, and troubleshoot authentication mismatches. Common issues include mismatched network types (broadcast vs. point-to-point), incorrect subnet masks, or missing OSPF network statements in router configuration. Understanding the relationship between OSPF neighbors, LSAs, and the SPF database is fundamental for ensuring network stability and efficient route propagation.
Question 94:
Which protocol allows multiple VLANs to traverse a single physical link?
A) 802.1Q Trunking
B) Access VLAN
C) EtherChannel
D) STP
Answer:
A)
Explanation:
IEEE 802.1Q trunking is a protocol used to enable multiple VLANs to traverse a single physical link between switches. This capability is critical in enterprise networks where multiple logical networks must coexist on the same physical infrastructure while remaining segregated for security and management purposes.
Each frame that passes through a trunk link is tagged with a VLAN identifier, known as the 802.1Q tag. This tag allows receiving switches to identify which VLAN the traffic belongs to, ensuring proper segmentation and forwarding. The only exception is the native VLAN, which is sent untagged by default; untagged frames arriving on a trunk port are assumed to belong to the native VLAN.
Trunking is commonly used in inter-switch connections, connections to routers for inter-VLAN routing, and connections to servers that need access to multiple VLANs. Access VLANs, by contrast, are assigned to individual switch ports and carry traffic for a single VLAN only. EtherChannel aggregates multiple physical links into a single logical link for redundancy and increased bandwidth but does not handle VLAN tagging by itself. Spanning Tree Protocol (STP) prevents Layer 2 loops in networks with redundant links but does not carry VLAN information.
CCNA candidates must understand how to configure trunk ports using commands like switchport mode trunk and switchport trunk allowed vlan, verify trunking with show interfaces trunk, and troubleshoot issues such as VLAN mismatches or misconfigured native VLANs. Proper trunk configuration ensures efficient VLAN communication, maintains network segmentation, and prevents broadcast storms.
Additionally, candidates should understand that improper trunking can result in VLAN leakage, connectivity issues, or misrouting of VLAN traffic. Real-world troubleshooting often involves verifying VLAN membership, ensuring VLANs exist on both ends of the trunk, and confirming STP convergence to avoid loops. Knowledge of 802.1Q is essential not only for the CCNA exam but also for configuring secure, scalable LAN architectures in enterprise environments.
Question 95:
Which IP address range is used for private networks?
A) 10.0.0.0 – 10.255.255.255
B) 192.0.2.0 – 192.0.2.255
C) 8.8.8.0 – 8.8.8.255
D) 172.32.0.0 – 172.63.255.255
Answer:
A)
Explanation:
The IP address range 10.0.0.0 – 10.255.255.255, also referred to as the 10.0.0.0/8 network, is reserved for private network use according to RFC 1918. Private IP addresses allow internal communication within an organization without requiring globally routable IPs, conserving IPv4 address space and simplifying network management.
Organizations can use these addresses for internal hosts, servers, and networking devices. Private addresses are not routed on the public internet, so Network Address Translation (NAT) or Port Address Translation (PAT) is required for internet access. Other private ranges include 172.16.0.0 – 172.31.255.255 and 192.168.0.0 – 192.168.255.255. Addresses like 192.0.2.0/24 are reserved for documentation and example networks, while 8.8.8.0/24 is a public Google DNS range, not suitable for private networks.
CCNA candidates must understand subnetting private networks to optimize address utilization, avoid overlaps, and design scalable network architectures. NAT configuration and verification are also critical, including commands like ip nat inside source list <ACL> interface <interface> overload. Proper use of private IPs ensures internal network security, supports IP reuse across branches, and provides compatibility with VPNs and other secure remote access solutions.
In practical deployments, understanding private addressing is essential for troubleshooting connectivity issues, configuring DHCP pools, and planning hierarchical addressing schemes. CCNA candidates should also recognize potential conflicts caused by overlapping private address ranges in merged networks and how NAT can resolve such conflicts for seamless communication.
Question 96:
Which NAT type allows multiple devices to share a single public IP using ports?
A) PAT
B) Static NAT
C) Dynamic NAT
D) NAT64
Answer:
A)
Explanation:
Port Address Translation (PAT), often referred to as “overload NAT,” allows multiple private IP addresses to share a single public IP by differentiating traffic using source port numbers. This technique is essential for conserving IPv4 addresses, particularly in organizations where many hosts need internet access through limited public IP addresses.
PAT maps each internal host’s private IP and port to the public IP and a unique port number. When a response arrives from the internet, the router translates the destination public IP and port back to the appropriate private IP and port. This method supports many-to-one NAT translation, which is efficient and widely used in home and enterprise networks.
Static NAT maps a single private IP to a single public IP (one-to-one), while dynamic NAT maps private IPs to a pool of public IPs (one-to-many, limited by pool size). NAT64 enables communication between IPv6 and IPv4 networks. CCNA candidates must understand how to configure PAT using access control lists (ACLs) and NAT commands, verify translations with show ip nat translations, and troubleshoot connectivity issues caused by port conflicts, ACL misconfigurations, or translation failures.
In real-world deployments, PAT is fundamental for enabling internet connectivity while conserving public IP resources. Understanding its operational principles, limitations, and integration with security policies is crucial for CCNA-level network design, planning, and troubleshooting.
Question 97:
Which routing protocol uses hop count as its metric?
A) RIP
B) OSPF
C) EIGRP
D) BGP
Answer:
A)
Explanation:
Routing Information Protocol (RIP) is a distance-vector routing protocol that uses hop count as its sole metric for selecting the best path. The maximum hop count allowed is 15, with 16 considered unreachable. This simplicity makes RIP suitable for small networks but limits its scalability in larger environments.
RIP operates by periodically broadcasting the entire routing table to neighboring routers. Routers then increment the hop count for each received route and update their own tables if a better path is found. This process can lead to slow convergence and routing loops in complex networks, which is why RIP has largely been replaced by more advanced protocols like OSPF and EIGRP in enterprise networks.
OSPF calculates path cost based on bandwidth, EIGRP uses composite metrics including bandwidth, delay, load, and reliability, and BGP is a path-vector protocol focused on interdomain routing. CCNA candidates should understand RIP configuration commands, timers, route summarization, and verification with show ip route and debug ip rip. Troubleshooting often involves resolving inconsistent hop counts, split horizons, or route poisoning scenarios.
Understanding RIP provides foundational knowledge of distance-vector protocols, convergence issues, and basic routing principles, which are crucial for CCNA-level routing and network troubleshooting.
Question 98:
Which command displays interface IP addresses and 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 provides a concise overview of all router or switch interfaces, displaying assigned IP addresses, operational status, and protocol state. This command is fundamental for verifying interface readiness and diagnosing Layer 3 connectivity issues.
The output includes interface names, IP addresses, status (up/down), and protocol status (up/down). This helps identify misconfigured or inactive interfaces, IP conflicts, or connectivity failures. For example, an interface may appear administratively up but protocol down, indicating issues like missing cables, misconfigured VLANs, or mismatched duplex/speed settings.
Other commands such as show running-config display the full device configuration, show vlan brief lists VLAN assignments, and show mac address-table provides Layer 2 MAC address mappings. CCNA candidates should routinely use show ip interface brief for troubleshooting, verifying connectivity after configuration changes, and confirming interface assignments during VLAN or routing deployments.
Mastering this command allows network engineers to quickly identify and isolate problems, ensuring operational efficiency and minimal downtime. It is a vital tool for lab exercises, real-world troubleshooting, and CCNA exam scenarios.
Question 99:
Which protocol translates hostnames into IP addresses?
A) DNS
B) DHCP
C) ARP
D) ICMP
Answer:
A)
Explanation:
The Domain Name System (DNS) is a hierarchical and distributed naming system used to translate human-readable hostnames into IP addresses, which are required for network communication. DNS is fundamental to network operations, as it allows users and applications to access resources using familiar names instead of memorizing numeric IP addresses.
When a user types a website URL into a browser, the operating system sends a DNS query to a DNS server to resolve the hostname to an IP address. This process may be recursive, where the server queries other DNS servers on behalf of the client, or iterative, where the client receives referrals to other servers until resolution occurs. DNS also supports caching, reducing query times and improving network efficiency.
DHCP, by contrast, assigns dynamic IP addresses to hosts; ARP resolves IP addresses to MAC addresses within a local network; ICMP is used for network diagnostics and error messaging. DNS operates at the application layer, is protocol-independent, and supports both IPv4 and IPv6 address resolution.
CCNA candidates must understand DNS operation, including the role of authoritative and recursive servers, forward and reverse lookups, and common record types like A, AAAA, CNAME, and MX. Troubleshooting DNS involves using tools like nslookup or ping with hostnames, checking server reachability, and verifying zone files and configurations.
In real-world enterprise networks, DNS is critical for service availability, load balancing, and security. Misconfigured or unreachable DNS can disrupt access to applications, servers, and the internet. Understanding DNS deeply prepares candidates for designing scalable networks, ensuring reliable name resolution, and integrating DNS with security policies such as DNSSEC.
Question 100:
Which command displays active EIGRP neighbors?
A) show ip eigrp neighbors
B) show ip route
C) show running-config
D) show interfaces
Answer:
A)
Explanation:
The show ip eigrp neighbors command is a diagnostic tool that provides detailed information about active Enhanced Interior Gateway Routing Protocol (EIGRP) neighbor relationships. EIGRP is an advanced distance-vector routing protocol that uses the DUAL (Diffusing Update Algorithm) to calculate the shortest path to destinations efficiently.
This command lists neighbor IP addresses, interface associations, hold times, uptime, and sequence numbers. Proper neighbor formation is essential because EIGRP routers exchange routing updates only with active neighbors. If an adjacency fails, the router may not have complete or accurate routing information, leading to potential network outages or suboptimal routing.
Other commands such as show ip route provide the routing table, show running-config displays configuration details, and show interfaces shows interface status but do not directly show EIGRP neighbor information. CCNA candidates must understand how to interpret neighbor relationships, verify hello and hold timers, and troubleshoot adjacency issues caused by mismatched K-values, authentication errors, or interface misconfigurations.
Real-world troubleshooting includes examining logs, verifying EIGRP autonomous system numbers, and confirming that network statements correctly cover the interfaces. Understanding EIGRP neighbor behavior also helps in optimizing convergence and preventing routing loops, which is essential for enterprise-grade reliability. Mastery of this command ensures candidates can verify and maintain robust EIGRP operations in both exam and practical scenarios.
Question 101:
Which IPv6 address type allows one-to-many communication?
A) Multicast
B) Unicast
C) Anycast
D) Link-local
Answer:
A)
Explanation:
The correct answer is A) Multicast. In IPv6 networking, multicast addresses are specifically designed to enable one-to-many communication, where a single packet sent by a source device is delivered to multiple destinations that are members of a multicast group. This approach is far more efficient than using multiple unicast transmissions for the same data, as it reduces bandwidth consumption and improves network performance. Multicast is a fundamental concept in both IPv4 and IPv6 networks, but IPv6 expands its usage and simplifies addressing to enhance communication efficiency in modern networks.
Multicast addresses in IPv6 always start with the prefix FF00::/8, which identifies the packet as intended for multiple devices. This allows routers and switches to recognize multicast traffic and forward it only to the networks or devices that have explicitly joined the multicast group, rather than flooding the traffic to all nodes. Membership in a multicast group is typically managed using the Internet Group Management Protocol (IGMP) in IPv4 or Multicast Listener Discovery (MLD) in IPv6, which enables devices to signal their interest in receiving traffic for specific multicast addresses.
The primary benefit of using multicast is efficient resource utilization. For example, streaming video, IPTV, or real-time stock updates can be transmitted to multiple clients simultaneously without sending individual streams to each client. This reduces the processing and bandwidth requirements on the source device and intermediate network devices, preventing unnecessary congestion. In enterprise networks, multicast is also used for routing protocol updates, such as OSPF or EIGRP, which rely on one-to-many communication to distribute routing information to all neighboring routers.
Unicast, by contrast, is one-to-one communication, where a packet is sent from one source to a single destination. Anycast addresses, while sharing similarities with multicast in that multiple devices may respond to the same address, are primarily used to deliver a packet to the nearest or best destination among multiple candidates, not to all devices. Link-local addresses are used for communication between nodes on the same link and are essential for operations like neighbor discovery but do not inherently provide one-to-many communication.
Implementing multicast requires careful network planning, including configuring routers and switches to support multicast routing protocols such as Protocol Independent Multicast (PIM). PIM enables efficient routing of multicast traffic across complex network topologies, ensuring packets reach all intended recipients without unnecessary duplication or flooding. Network administrators must also monitor multicast group membership and ensure that devices are properly configured to join the correct multicast groups to receive relevant traffic.
Understanding IPv6 multicast addressing and its operational mechanisms is a key component of CCNA-level knowledge, as it impacts both network efficiency and application performance. By using multicast, networks can scale more effectively, handle large numbers of simultaneous recipients, and reduce overall resource consumption. Proper implementation ensures reliable one-to-many communication while maintaining optimal network performance and avoiding congestion caused by redundant transmissions.
In summary, IPv6 multicast addresses allow one-to-many communication by delivering packets to multiple destinations that are members of a multicast group. They provide efficient bandwidth usage, reduce redundant transmissions, and are widely used in applications such as media streaming, routing updates, and service announcements. Mastery of multicast concepts, address types, and protocols is essential for network design, troubleshooting, and CCNA certification success.
Question 102:
Which command shows the routing table on a router?
A) show ip route
B) show interfaces
C) show vlan brief
D) show mac address-table
Answer:
A)
Explanation:
The correct answer is A) show ip route. The show ip route command is one of the most fundamental and frequently used commands in Cisco networking and is essential for CCNA candidates and network administrators to understand the current state of a router’s IP routing table. This command provides detailed information about the routes that a router knows, how it learned them, and how it will forward traffic to different network destinations. Understanding the output of this command is crucial for diagnosing connectivity issues, verifying routing configurations, and planning network designs effectively.
When executed, show ip route displays all active routes in the routing table, including directly connected networks, static routes, and dynamically learned routes from routing protocols such as OSPF, EIGRP, RIP, or BGP. Each route is typically marked with a code that indicates how the router learned the route. For example, C denotes a directly connected network, S indicates a static route, O represents an OSPF-learned route, D signifies EIGRP, and R is for RIP. This information allows network administrators to quickly determine the origin of a route and verify whether the routing table aligns with the intended network design.
The output also includes important details such as the destination network, subnet mask, next-hop IP address, exit interface, and administrative distance. The destination network and subnet mask define the network segment being reached, while the next-hop IP address specifies the next device to forward packets to. The exit interface shows which router interface will be used to send traffic toward the destination. Administrative distance is a measure of the trustworthiness of a route; routes with lower administrative distance values are preferred over others when multiple paths exist to the same destination.
For troubleshooting, the show ip route command is invaluable. It helps identify missing routes, incorrect next-hop addresses, or misconfigured static routes that may prevent traffic from reaching its destination. When combined with other commands such as ping or traceroute, it allows administrators to isolate network issues efficiently, determine if traffic is being routed correctly, and confirm the operational status of dynamic routing protocols.
Additionally, this command assists in network planning and optimization. By reviewing the routing table, administrators can verify the efficiency of route summarization, identify redundant paths, and ensure optimal traffic flow. For CCNA-level knowledge, understanding how different routing protocols populate the routing table, how metrics and administrative distances influence path selection, and how to interpret route types are key skills.
In larger networks, show ip route also provides insight into how dynamic routing updates are reflected in the table, including routes redistributed from other protocols or learned via external sources. This ensures that traffic follows intended paths and avoids routing loops or suboptimal routing decisions.
Question 103:
Which IPv6 address type allows one-to-nearest communication?
A) Anycast
B) Unicast
C) Multicast
D) Link-local
Answer:
A)
Explanation:
The correct answer is Anycast, which is an IPv6 addressing method that allows a single address to be assigned to multiple devices in a network, enabling one-to-nearest communication. Anycast addresses are primarily used to improve network efficiency, reduce latency, and provide redundancy by directing traffic to the closest or best-performing node based on routing metrics. When a packet is sent to an anycast address, the network routing infrastructure determines which of the multiple devices assigned that address is nearest, typically using the lowest-cost path in terms of routing protocol metrics.
Anycast addresses are commonly deployed in scenarios such as content delivery networks (CDNs), distributed services, DNS servers, and load-balancing architectures. For example, a global DNS service may assign the same anycast address to multiple servers located in different regions. When a client sends a query to this anycast address, the network ensures that the request is routed to the server closest to the client, reducing latency and improving the overall user experience. This approach also enhances fault tolerance. If one node becomes unavailable, traffic is automatically redirected to the next nearest node without requiring changes at the client side.
Unlike unicast, which establishes one-to-one communication, anycast is inherently one-to-nearest or one-to-one-of-many. Multicast, by contrast, sends data to multiple specific recipients at once, while link-local addresses are used for communication within the local network segment and are not designed for routing across multiple networks. Anycast uniquely combines features of unicast and multicast by using a single address for multiple destinations while ensuring that traffic is routed efficiently to the nearest available node.
Configuring anycast in IPv6 is achieved by assigning the same IP address to multiple devices and allowing the routing protocol to determine the optimal path. Routing protocols such as OSPFv3, BGP, or IS-IS can be configured to support anycast addressing, ensuring that the closest device responds to traffic. This approach simplifies client configuration because clients do not need to know about multiple server locations; they only need the single anycast address.
Network administrators benefit from anycast in terms of scalability and resilience. Since multiple devices can share the same address, traffic load can be distributed geographically, preventing any single device from becoming a bottleneck. It also increases reliability because if a node fails, routing protocols automatically redirect traffic to another node using the same anycast address.
In , anycast is the correct IPv6 address type for one-to-nearest communication because it allows a single IP address to be used by multiple devices while ensuring traffic is delivered to the closest or most optimal node. This addressing scheme improves performance, enhances redundancy, simplifies client configuration, and provides a scalable solution for global and distributed network services.
Question 104:
Which command displays detailed STP information, including root bridge 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 correct answer is A) show spanning-tree detail. The show spanning-tree detail command is a critical tool for network administrators and CCNA candidates to gain in-depth insights into the Spanning Tree Protocol (STP) configuration and operation on Cisco switches. This command provides detailed information about the STP topology, which is essential for preventing Layer 2 loops in networks with redundant paths. By analyzing the output of this command, administrators can understand the state of each interface, determine the root bridge, and identify port roles and timers, all of which are vital for maintaining a stable and loop-free network.
When executed, show spanning-tree detail displays information such as the root bridge ID, the bridge priority, the root port, designated ports, and nondesignated ports. The root bridge ID identifies the switch that has been elected as the root of the spanning tree topology, and understanding this allows engineers to verify that the root bridge election aligns with network design. Port roles indicate how each interface participates in the STP topology: root ports forward traffic toward the root bridge, designated ports forward traffic for the segment, and nondesignated ports are typically blocked to prevent loops. This level of detail is crucial for troubleshooting connectivity issues or misconfigurations that may cause loops or broadcast storms.
The output also includes port states such as blocking, listening, learning, forwarding, and disabled. Each state represents a stage in the STP convergence process. For instance, a port in the blocking state does not forward frames and is considered a redundant path, while a forwarding port actively forwards frames in the network. Timers for hello, forward delay, and max age are also displayed, helping administrators analyze convergence times and optimize network performance. Path costs, calculated based on interface speed, are shown for each port to indicate the least-cost path toward the root bridge, which assists in understanding traffic flow in complex topologies.
Understanding and interpreting the detailed STP information is crucial for implementing STP enhancements and best practices. CCNA candidates and network engineers should be familiar with concepts like PVST (Per-VLAN Spanning Tree), RSTP (Rapid Spanning Tree Protocol), and MSTP (Multiple Spanning Tree Protocol), which provide faster convergence and VLAN-specific configurations. Features such as PortFast, BPDU Guard, and root guard rely on correctly understanding the spanning tree topology, which can be verified and monitored using the show spanning-tree detail command.
Additionally, this command is invaluable for troubleshooting network outages caused by misconfigured STP parameters. A misconfigured priority or path cost may result in a suboptimal root bridge selection, leading to traffic congestion or blocked ports that disrupt connectivity. By using show spanning-tree detail, administrators can pinpoint the exact cause of STP-related issues, adjust configurations, and ensure efficient and resilient network operation.
Question 105:
Which command allows verification of interface operational status and IP addresses?
A) show ip interface brief
B) show running-config
C) show vlan brief
D) show mac address-table
Answer:
A)
Explanation:
The correct answer is show ip interface brief, a commonly used Cisco IOS command that provides a concise overview of all interfaces on a router or switch, including their operational status, IP address, and protocol state. This command is a fundamental tool for network administrators to quickly verify the health, configuration, and connectivity of interfaces, allowing efficient troubleshooting and monitoring of network devices.
When executed, the show ip interface brief command produces a table listing each interface, its IP address, interface status (administratively up or down), protocol status (whether the interface protocol is up or down), and description if configured. This allows administrators to quickly identify interfaces that are inactive or misconfigured, such as interfaces administratively shut down or interfaces with missing IP addresses, which can cause connectivity issues.
For example, if a network host cannot reach a router or another network segment, administrators can use this command to confirm whether the corresponding interface is operational and correctly configured with the proper IP address. This visibility is critical for identifying misconfigurations that may cause network outages, including incorrect subnet masks, missing IP assignments, or disabled interfaces.
In addition to troubleshooting connectivity problems, show ip interface brief is frequently used during routine network audits and verification tasks. When adding new devices or interfaces to a network, the command allows administrators to confirm that interfaces are active and properly assigned to the correct IP subnets. In larger environments, where devices have dozens of interfaces, the command’s concise output makes it easier to locate and manage specific interfaces without needing to scroll through lengthy configuration files.
Other commands listed do not provide the same level of immediate interface operational information. show running-config displays the full configuration of the device, including interface configurations, routing protocols, and other parameters, but it does not directly indicate whether an interface is currently up or down. show vlan brief shows VLAN configuration and membership for switch interfaces but does not display IP addresses or Layer 3 interface status. show mac address-table lists MAC addresses associated with switch ports, providing Layer 2 information, but it does not verify interface IP configuration or protocol state.
Using show ip interface brief also helps in proactive network management. Administrators can detect issues like misaligned IP schemes, incorrect VLAN assignments on routed interfaces, or interfaces in a down state before they affect end users. This command is useful when preparing for network expansion, migrations, or when performing troubleshooting for intermittent connectivity issues.
Show ip interface brief is the correct command because it provides a quick and efficient way to verify the operational status of interfaces, confirm assigned IP addresses, and identify interfaces that are administratively or operationally down. Its concise format, immediate visibility, and focus on interface health make it an essential tool for network monitoring, troubleshooting, and administration.