Cisco 350-401 Implementing Cisco Enterprise Network Core Technologies (ENCOR) Exam Dumps and Practice Test Questions Set 5 Q61-75
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Question 61
Which protocol is used by Layer 3 devices to dynamically discover neighbouring routers and learn about their capabilities?
A) CDP
B) LLDP
C) OSPF
D) EIGRP
Answer: B) LLDP
Explanation:
CDP, or Cisco Discovery Protocol, is a proprietary Cisco protocol used for discovering directly connected devices, but it only works between Cisco devices. OSPF is a link-state routing protocol that allows routers to learn network topology, but is not specifically designed for neighbour discovery at Layer 2. EIGRP is a hybrid routing protocol used for efficient route learning and path selection within an autonomous system, but it does not focus on device capability discovery. LLDP, or Link Layer Discovery Protocol, is a standards-based Layer 2 protocol that allows devices to advertise information about themselves to directly connected devices. LLDP operates in a vendor-neutral manner, which means devices from different manufacturers can share their identity, capabilities, and management addresses. It provides critical information such as device type, interface identifiers, system name, and capabilities (like whether the device is a router, switch, or VoIP phone). LLDP packets are periodically sent to a reserved multicast address, enabling neighbours to build a database of directly connected devices. This information assists network administrators in mapping network topology, verifying device connections, troubleshooting misconfigurations, and planning network expansions. LLDP is particularly useful in multi-vendor environments where CDP would not work. The protocol also helps in advanced scenarios such as Power over Ethernet (PoE) management and VLAN assignment. Therefore, the correct answer is LLDP because it allows Layer 3 and Layer 2 devices to dynamically discover neighbours, learn device capabilities, and exchange detailed management information in a vendor-neutral way.
Question 62
Which protocol is commonly used to monitor and manage network devices by collecting device information and statistics?
A) SNMP
B) RADIUS
C) TACACS+
D) ICMP
Answer: A) SNMP
Explanation:
RADIUS provides authentication, authorisation, and accounting (AAA) for network access, but does not collect device statistics. TACACS+ is also an AAA protocol for secure device access management and auditing, but it is not intended for monitoring network performance. ICMP is used for network diagnostics,s, such as ping or traceroute, but does not gather detailed device information. SNMP, or Simple Network Management Protocol, is the industry-standard protocol used for monitoring and managing network devices like routers, switches, firewalls, and servers. SNMP enables administrators to collect statistics such as CPU usage, memorutilisationon, interface traffic, error rates, and device status. The protocol uses a manager-agent model, where network devices run an SNMP agent that communicates with an SNMP manager to report data. SNMP supports polling, traps, and notifications, allowing proactive monitoring and alerting for faults or performance degradation. Administrators can also configure SNMP communities or use SNMPv3 for secure communication, ensuring sensitive device data is protected. In enterprise networks, SNMP is essential for performance monitoring, capacity planning, and troubleshooting. It allows visualisation of network health, helps in identifying bottlenecks, and enables rapid response to anomalies. Therefore, the correct answer is SNMP because it provides a comprehensive mechanism for monitoring and managing network devices, collecting detailed operational statistics, and enabling proactive network administration.
Question 63
Which IPv6 address type allows packets to reach all devices within a specified group?
A) Unicast
B) Multicast
C) Anycast
D) Link-local
Answer: B) Multicast
Explanation:
Unicast addresses are used for one-to-one communication, delivering packets to a single interface. Anycast addresses are shared among multiple devices, with packets delivered to the nearest device, making them suitable for load balancing but not group delivery. Link-local addresses are automatically configured on interfaces for communication within a single subnet but do not support group delivery. Multicast addresses are specifically designed to deliver a single packet to multiple interfaces that have joined a particular multicast group. Devices interested in receiving the multicast traffic subscribe to the multicast group, and routers forward traffic only to network segments containing members of that group. This approach reduces unnecessary broadcast traffic, conserves bandwidth, and improves efficiency compared to sending multiple unicast messages. IPv6 eliminates the need for traditional broadcast addresses, relying on multicast for group communication. Protocols such as OSPFv3, EIGRP for IPv6, and streaming media applications use multicast addresses extensively for efficient communication. Multicast improves scalability in large networks by targeting only interested devices instead of sending traffic to all devices. Therefore, the correct answer is Multicast because it allows a packet to be delivered to all devices within a specified group, improving network efficiency and enabling targeted communication.
Question 64
Which Cisco technology allows multiple switches to appear as a single logical switch to simplify management and increase redundancy?
A) StackWise
B) VTP
C) EtherChannel
D) HSRP
Answer: A) StackWise
Explanation:
VTP propagates VLAN information across switches but does not unify management or create a single logical switch. EtherChannel aggregates physical links into one logical link but does not combine multiple switches for centralised management. HSRP provides gateway redundancy but does not affect switch management. StackWise interconnects multiple physical switches to operate as a single logical unit. The stack has a master switch controlling the stack while member switches function under its management, allowing centralised configuration and monitoring. StackWise simplifies administration by consolidating control plane operations and management IP addresses, while ports from different switches in the stack can be used interchangeably, providing flexibility. It also improves redundancy; if one switch fails, the others continue forwarding traffic, minimising downtime. StackWise supports unified spanning-tree computation, ensuring consistent Layer 2 topologies across the stack. In enterprise networks, StackWise enhances scalability, simplifies management, and provides fault tolerance. Therefore, the correct answer is StackWise because it allows multiple switches to operate as a single logical switch, reducing complexity and improving network reliability.
Question 65
Which NAT mechanism allows many private IP addresses to share a single public IP address using unique port numbers for each session?
A) Static NAT
B) Dynamic NAT
C) PAT
D) NAT64
Answer: C) PAT
Explanation:
In modern network environments, translating private IP addresses to public addresses is essential for enabling devices on internal networks to communicate with external networks such as the Internet. Network Address Translation (NAT) provides several mechanisms for achieving this, each with different capabilities and use cases. Among the common forms are static NAT, dynamic NAT, NAT64, and Port Address Translation (PAT), also known as NAT overload. Understanding the differences between these methods clarifies why PAT is the optimal solution for enabling multiple devices to share a single public IP while maintaining connectivity and session integrity.
Static NAT is a straightforward approach in which a specific private IP address is mapped directly to a single public IP address. This method is commonly used for servers that must be accessible from the Internet, such as web servers, email servers, or VPN gateways. While static NAT ensures that external users can consistently reach a specific device, it does not allow multiple devices to share the same public IP. Each internal host requires its own unique public address, which can become impractical in networks with many devices and limited public IP resources.
Dynamic NAT provides a more flexible approach by using a pool of public IP addresses. Internal devices are mapped to an available public IP from this pool on a one-to-one basis, allowing multiple hosts to access external networks over time. While dynamic NAT increases the efficient use of public addresses compared to static NAT, it still limits reuse, as each active session consumes one public IP. If the pool of available public addresses is exhausted, additional devices cannot access the Internet until addresses are freed.
NAT64 is a specialised form of translation that enables IPv6-only devices to communicate with IPv4 networks. It translates IPv6 traffic into IPv4 and vice versa, facilitating interoperability in dual-stack networks during IPv6 transition periods. Although NAT64 solves the challenge of IPv6-to-IPv4 communication, it is not designed for scenarios where multiple private IPv4 devices need to share a single public IPv4 address. Its function is primarily protocol translation rather than address conservation for multiple hosts.
Port Address Translation, or PAT, addresses these limitations effectively. PAT allows multiple devices on a private network to access external resources using a single public IP address. It achieves this by mapping each internal device’s IP address and port number to a unique port on the shared public IP. This mapping enables the router or NAT device to maintain session information for all active connections, ensuring that responses from external hosts are correctly routed back to the originating internal device. PAT is highly efficient, allowing dozens, hundreds, or even thousands of internal devices to access the Internet simultaneously without requiring a proportional number of public IP addresses.
PAT also simplifies network design by conserving public IP addresses and reducing administrative overhead. Enterprises with limited IPv4 addresses can provide Internet access to all employees and internal systems without acquiring a large pool of public IPs. Similarly, in home networks, PAT allows multiple devices such as laptops, smartphones, and smart home devices to share a single ISP-provided public IP while maintaining independent sessions. By tracking port numbers and session states, PAT ensures that all devices receive accurate and timely responses, maintaining a seamless user experience even when many connections are active concurrently.
While static NAT provides dedicated mappings for specific devices, dynamic NAT allows limited pool-based address sharing, and NAT64 facilitates IPv6-to-IPv4 translation; only PAT enables multiple devices to share a single public IP effectively. By using unique port numbers to distinguish sessions, PAT conserves public address space, ensures accurate routing of return traffic, and provides scalable Internet connectivity for networks of all sizes. Its ability to combine address conservation with reliable session management makes it the preferred method for connecting multiple private IP devices to external networks efficiently.
Question 66
Which protocol allows routers to exchange routing information within a single autonomous system using distance-vector metrics?
A) OSPF
B) RIP
C) EIGRP
D) BGP
Answer: B) RIP
Explanation:
OSPF is a link-state routing protocolwhthatses the Dijkstra algorithm and a full topology database to calculate the shortest path. It is not based purely on distance-vector metrics. EIGRP is a hybrid protocol, using a combination of distance-vector and link-state features for more intelligent routing, but it is not a pure distance-vector protocol. BGP is a path-vector protocol used primarily for inter-domain routing between autonomous systems and does not rely solely on distance-vector metrics. RIP, or Routing Information Protocol, is a classic distance-vector protocol where routers exchange information about reachable networks with neighbouring routers periodically. RIP uses hop count as its primary metric, with a maximum hop count of 15, making it unsuitable for very large networks.
Each router periodically sends its entire routing table tneighbourssrs, and convergence occurs gradually, which can lead to slow recovery in case of failures. Despite its simplicity, RIP is still useful for small networks or as a learning tool. The protocol supports classful and classless addressing depending on version (RIP v1 is classful, RIP v2 supports classless routing). RIP is straightforward to configure and understand, but it lacks advanced features such as fast convergence, multiple metrics, and support for variable-length subnet masks compared to modern protocols. In an enterprise network, RIP’s simplicity might be beneficial in isolated or legacy environments, but it is generally replaced by OSPF or EIGRP for better scalability and efficiency. Therefore, the correct answer is RIP because it allows routers within a single autonomous system to exchange routing information using distance-vector metrics, relying primarily on hop count to determine the best path.
Question 67
Which IPv6 address type is used for communication within a single subnet and is automatically configured on all IPv6-enabled interfaces?
A) Global unicast
B) Link-local
C) Multicast
D) Anycast
Answer: B) Link-local
Explanation:
Global unicast addresses are routable across the Internet and are not limited to a single subnet. Multicast addresses deliver packets to multiple devices subscribed to a group rather than just within a single subnet. Anycast addresses are shared among multiple devices, and packets are delivered to the nearest device according to routing metrics. Link-local addresses, however, are automatically generated on all IPv6-enabled interfaces and are used exclusively for communication within the same subnet. They are mandatory for IPv6 operation and are essential for core network functionalities like neighbour discovery, router advertisements, and routing protocol exchanges such as OSPFv3 or EIGRP for IPv6. Each interface typically derives a link-local address from its MAC address using the modified EUI-64 format or can be manually configured. Because link-local addresses are non-routable, they remain confined to the local link, ensuring safe and efficient communication without exposure to external networks. They also provide a guaranteed address that all IPv6 devices will have, allowing IPv6 protocols to operate even without global unicast configuration. Therefore, the correct answer is Link-local because it is automatically configured, mandatory, and used for essential local subnet communication and routing functions.
Question 68
Which Cisco feature provides redundancy for default gateways in a Layer 3 network?
A) EtherChannel
B) HSRP
C) STP
D) VTP
Answer: B) HSRP
Explanation:
EtherChannel aggregates multiple physical links into a single logical link to increase bandwidth, but does not provide gateway redundancy. STP prevents Layer 2 switching loops but does not address default gateway availability. VTP synchronises VLAN information but does not offer redundancy. HSRP, or Hot Standby Router Protocol, is a Cisco proprietary protocol that ensures default gateway redundancy. Multiple routers participate in an HSRP group, but only one router actively forwards traffic as the primary gateway. Other routers in the group remain in standby mode and take over if the active router fails, providing continuous network availability. HSRP assigns a virtual IP address and a virtual MAC address shared by all routers in the group, which is configured as the default gateway on hosts. The protocol monitors the active router’s state and automatically fails over to a standby router if necessary. HSRP is critical in enterprise networks to prevent single points of failure for the default gateway, ensuring uninterrupted connectivity for devices in the VLAN. Rapid HSRP (Version 2) improves convergence times, further enhancing network reliability. Therefore, the correct answer is HSRP because it provides redundancy for default gateways, allowing seamless failover and maintaining continuous network availability.
Question 69
Which protocol allows a Layer 2 switch to synchronise VLAN information across multiple switches?
A) STP
B) VTP
C) DTP
D) CDP
Answer: B) VTP
Explanation:
In modern enterprise networks, managing VLAN configurations across multiple switches can be a complex and error-prone task, especially in large-scale environments with dozens or hundreds of switches. Without a centralised mechanism, network administrators must configure VLANs individually on each switch, which increases the risk of inconsistencies, misconfigurations, and operational inefficiencies. Cisco provides several protocols that assist with different aspects of Layer 2 networking, such as loop prevention, trunk negotiation, and neighbour discovery. However, when it comes tsynchronisingng VLAN information across multiple switches, VLAN Trunking Protocol, or VTP, is the solution designed specifically for this purpose.
Spanning Tree Protocol, or STP, is an essential Layer 2 protocol that prevents network loops by selectively blocking redundant paths. It ensures network stability and avoids broadcast storms that can occur in redundant network topologies. While STP is critical for loop prevention, it does not provide any mechanism for distributing VLAN configurations between switches.
Dynamic Trunking Protocol, or DTP, is a Cisco-proprietary protocol that automates the negotiation of trunk links between switches. By dynamically determining whether a link should operate as a trunk or an access port, DTP reduces manual configuration effort and ensures that VLAN traffic can traverse the network appropriately. However, DTP does not manage or propagate VLAN information itself; it only facilitates the transport of VLAN traffic across established trunk links.
Cisco Discovery Protocol, or CDP, is another Layer 2 protocol that enables switches and other Cisco devices to discover neighbouring devices. CDP provides visibility into directly connected devices and their capabilities, which is useful for troubleshooting and network mapping. Despite its benefits in network awareness, CDP does not provide any function forsynchronisingg VLAN configurations across multiple switches.
VLAN Trunking Protocol, or VTP, is explicitly designed to solve the problem of consistent VLAN management in multi-switch environments. VTP allows administrators to create, modify, or delete VLANs on a single switch designated as a VTP server, and those changes are automatically propagated to all other switches in the same VTP domain that are operating as clients. This centralised approach ensures that every switch in the domain maintains a consistent VLAN configuration, minimising configuration errors and reducing administrative overhead.
VTP operates in multiple modes to provide flexibility in network design. In server mode, a switch can create, modify, and delete VLANs, with changes propagated to all client switches. In client mode, a switch receives updates from VTP servers but cannot make VLAN changes independently. Transparent mode allows a switch to maintain its VLAN database independently while forwarding VTP messages to other switches, which is useful for isolating certain network segments. VTP also supports pruning, which prevents unnecessary VLAN traffic from traversing trunk links when no devices on a switch require that VLAN. This reduces broadcast traffic, improves network efficiency, and optimises bandwidth usage.
By implementing VTP, network engineers can manage VLANs centrally, enforce consistent configurations across large networks, and streamline ongoing network operations. The protocol reduces human errors, saves time, and ensures that VLAN changes are applied uniformly, which is especially valuable in dynamic environments where VLANs are frequently updated or restructured.
While STP, DTP, and CDP each serve important functions such as loop prevention, trunk negotiation, and neighbour discovery, VTP uniquely provides a mechanism for distributing and maintaining consistent VLAN configurations across multiple switches. By enabling centralised management, reducing broadcast traffic through pruning, and supporting multiple operational modes, VTP simplifies network administration and enhances the reliability and efficiency of Layer 2 networks. Therefore, the correct answer is VTP because it ensures synchronised VLAN information across all switches in a VTP domain, providing consistent configuration and streamlined management in enterprise networks.
Question 70
Which feature allows multiple private IP addresses to access the Internet using a single public IP address by differentiating sessions through unique ports?
A) Static NAT
B) Dynamic NAT
C) PAT
D) NAT64
Answer: C) PAT
Explanation:
Static NAT maps one private IP to one public IP and is suitable for servers, but does not allow multiple devices to share one public IP. Dynamic NAT assigns private IPs to public IPs from a pool on a one-to-one basis, which also does not enable multiple devices to share a single address. NAT64 translates IPv6 addresses to IPv4 addresses and is used for interoperability between protocols, but is not for sharing public IPs among multiple hosts. PAT, or Port Address Translation, also called NAT overload, enables multiple private IP addresses to share a single public IP address by assigning unique port numbers for each session. This allows many hosts to communicate simultaneously with external networks while conserving public IP addresses. The router tracks the mapping of internal IPs and ports to the public IP and ensures traffic is returned to the correct host. PAT is widely deployed in enterprise and home networks to optimise the use of the limited public IPv4 address space while maintaining connectivity. Therefore, the correct answer is PAT because it allows multiple private IP addresses to access the Internet through a single public IP using unique port numbers, ensuring efficient resource utilisation and reliable connectivity.
Question 71
Which protocol allows routers to dynamically exchange routes using link-state information and calculates the shortest path to each network?
A) RIP
B) OSPF
C) EIGRP
D) BGP
Answer: B) OSPF
Explanation:
In the realm of enterprise networking, selecting the appropriate routing protocol is critical for ensuring optimal performance, scalability, and reliability. Routing protocols determine how routers communicate with each other to exchange information about network topology and make decisions regarding the best paths for forwarding packets. There are multiple types of routing protocols, including distance-vector, link-state, hybrid, and path-vector protocols. Each of these protocols approaches route calculation differently, with distinct strengths and limitations. Understanding these differences helps clarify why Open Shortest Path First (OSPF) is the preferred solution for dynamic, intra-domain routing in complex enterprise networks.
RIP, or Routing Information Protocol, is one of the earliest distance-vector routing protocols. It calculates the best path to a destination solely based on hop count, which is the number of routers a packet must traverse to reach the target network. While RIP is simple to configure and understand, its reliance on hop count as the only metric can lead to suboptimal routing. Additionally, RIP does not maintain a complete view of the network topology; it only knows the next-hop distance to each destination. RIP’s convergence time is slow, especially in large networks, and it is limited to a maximum of 15 hops, making it unsuitable for complex enterprise environments.
EIGRP, or Enhanced Interior Gateway Routing Protocol, is a hybrid protocol that combines aspects of both distance-vector and link-state routing. It considers multiple metrics, including bandwidth, delay, load, and reliability, to calculate the most efficient paths. EIGRP also uses the Diffusing Update Algorithm (DUAL) to ensure loop-free and efficient routing. While EIGRP is highly capable and provides fast convergence, it is not a true link-state protocol. Unlike OSPF, it does not maintain a complete network-wide link-state database, and its routing decisions are based on metric calculations rather than a global view of the network topology. EIGRP is efficient and scalable within a single autonomous system but lacks some of the hierarchical design and area-based segmentation that OSPF offers.
BGP, or Border Gateway Protocol, is a path-vector protocol designed for inter-domain routing between autonomous systems, such as Internet service providers. BGP makes routing decisions based on policy and path attributes rather than link-state or network metrics like bandwidth or delay. While BGP excels at controlling routing policies across multiple administrative domains, it is not designed for rapid intra-domain convergence and does not maintain a detailed topology of all networks within a single autonomous system. Therefore, BGP is more appropriate for Internet-scale routing rather than enterprise internal networks.
OSPF, or Open Shortest Path First, is a link-state routing protocol specifically designed for dynamic routing within an autonomous system. Each OSPF router collects Link-State Advertisements (LSAs) from all routers in its area and builds a complete link-state database that represents the entire network topology. Using the Dijkstra shortest-path algorithm, every router independently calculates the shortest and most efficient paths to all reachable networks. This approach ensures that routing decisions are highly accurate, loop-free, and optimal. OSPF also supports hierarchical design through the use of areas, which reduces the size of routing tables, limits the scope of network changes, and improves overall scalability.
Additional OSPF features, such as route summarisation, authentication, and equal-cost multipath (ECMP) routing, further enhance network efficiency, security, and performance. In the event of link or router failures, OSPF can reconverge rapidly, minimising downtime and maintaining high network availability. Its ability to maintain a complete view of the network allows administrators to predict routing behaviour, redundancy planning, and optimise resource utilisation effectively.
While RIP is limited by its hop-count metric and slow convergence, EIGRP provides advanced metrics but lacks a true link-state view, and BGP focuses on inter-domain routing rather than internal network topology. OSPF stands out as the protocol that delivers accurate, scalable, and efficient routing within an enterprise. By dynamically learning routes, maintaining a complete link-state database, calculating shortest paths, and supporting hierarchical network design, OSPF ensures that enterprise networks remain reliable, resilient, and capable of handling complex, high-volume traffic demands. Therefore, OSPF is the most appropriate choice for dynamic intra-domain routing, providing optimal routing performance, rapid convergence, and operational efficiency in modern enterprise networks.
Question 72
Which IPv6 address type is used for sending a packet to all nodes on the same local link?
A) Unicast
B) Multicast
C) Anycast
D) Link-local
Answer: B) Multicast
Explanation:
In IPv6 networking, understanding the different types of addressing and their specific purposes is essential for designing efficient, scalable, and reliable networks. IPv6 introduces several address types, including unicast, anycast, link-local, and multicast, each serving distinct functions. Among these, multicast addresses play a critical role in enabling targeted communication with multiple devices while reducing unnecessary network traffic, particularly within a local link or subnet. To appreciate why multicast is uniquely suited for group communication, it is important to contrast it with other IPv6 address types and examine its practical applications.
Unicast addresses are the most straightforward type of IP address in IPv6. They identify a single interface on a device and deliver packets to that specific destination only. When a packet is sent to a unicast address, it is directed exclusively to the intended recipient, ensuring one-to-one communication. While unicast is fundamental for point-to-point data exchange, it is not suitable for sending the same information to multiple devices efficiently. Sending multiple unicast packets to reach several devices individually would consume excessive bandwidth and create unnecessary network load.
Anycast addresses are another specialised IPv6 address type. An anycast address can be assigned to multiple devices, and packets sent to this address are routed to the nearest device according to the routing protocol’s metric, such as hop count or cost. Anycast is widely used for services that require proximity-based delivery, such as DNS servers or content delivery networks. However, anycast is not intended for broadcasting information to all members of a group; it only delivers packets to a single, nearest node, which makes it unsuitable for scenarios requiring group communication.
Link-local addresses are automatically assigned to interfaces and are required for communication within the local link. These addresses are essential for basic operations such as neighbour discovery, router advertisements, and initial IPv6 configuration before global unicast addresses are assigned. While link-local addresses enable devices to communicate directly on the same link, they do not inherently provide a mechanism for sending information to multiple devices simultaneously. Each communication session remains essentially point-to-point, similar to unicast.
Multicast addresses, in contrast, are specifically designed for efficient one-to-many communication. A multicast address identifies a group of interfaces that have expressed interest in receiving packets sent to that address. When a packet is transmitted to a multicast address, all devices that have joined the associated multicast group receive it. For example, the all-nodes link-local multicast address (ff02::1) allows a packet to reach every device on the local link without the need to send individual unicast messages. This approach reduces network congestion and avoids the inefficiencies of traditional broadcast mechanisms, which are no longer used in IPv6.
Multicast is extensively utilised in IPv6 protocols to improve efficiency and scalability. Neighbour Discovery Protocol (NDP), for instance, uses multicast to propagate information about reachable devices, link addresses, and router availability. Routing protocols also leverage multicast to distribute updates efficiently to multiple nodes simultaneously. By targeting only the devices that have joined a multicast group, network traffic is minimised, ensuring that bandwidth is conserved and the network remains responsive even under heavy load.
Multicast also provides flexibility and selectivity. Network administrators can define multiple multicast groups based on applications, services, or administrative needs, allowing selective communication with only the relevant devices. This capability is critical in enterprise networks, where large numbers of devices require coordinated updates, service advertisements, or monitoring messages without overwhelming the network with redundant traffic.
While unicast delivers packets to a single device, anycast directs packets to the nearest of several nodes, and link-local addresses facilitate local link communication; only multicast enables targeted one-to-many delivery. By allowing a single packet to reach multiple devices on the same link efficiently, multicast reduces network congestion, supports scalable protocols, and facilitates group communication critical for enterprise and service-oriented network operations. Therefore, multicast is the appropriate solution when communication with multiple devices simultaneously is required, ensuring efficient, scalable, and manageable IPv6 networking.
Question 73
Which Cisco technology provides redundancy for default gateways by allowing multiple routers to share a virtual IP address?
A) HSRP
B) VRRP
C) GLBP
D) STP
Answer: A) HSRP
Explanation:
VRRP, or Virtual Router Redundancy Protocol, is a standards-based alternative to HSRP but is not proprietary to Cisco. GLBP, or Gateway Load Balancing Protocol, provides both redundancy and load balancing but is less commonly deployed than HSRP. STP prevents Layer 2 loops but does not provide default gateway redundancy. HSRP, or Hot Standby Router Protocol, is a Cisco proprietary protocol that allows multiple routers to share a single virtual IP and MAC address for hosts configured with that IP as their default gateway. One router is elected as the active router, handling all traffic, while others remain in standby mode. If the active router fails, a standby router takes over seamlessly, ensuring uninterrupted network access. HSRP provides a simple and reliable method to eliminate a single point of failure for the default gateway. Rapid HSRP improves convergence times in modern networks. It is widely used in enterprise VLANs where gateway availability is critical for network reliability and uptime. Therefore, the correct answer is HSRP because it provides default gateway redundancy by enabling multiple routers to share a virtual IP address, ensuring continuous network connectivity.
Question 74
Which Layer 2 technology prevents broadcast storms and loops in redundant switch topologies?
A) CDP
B) STP
C) VTP
D) EtherChannel
Answer: B) STP
Explanation:
In enterprise network design, ensuring stability and preventing disruptions is a fundamental requirement, especially in Layer 2 topologies where multiple switches are interconnected to provide redundancy. Redundant paths are critical for maintaining high availability, but they can also introduce serious challenges such as loops and broadcast storms if not properly managed. Various network protocols and technologies provide different functionalities, but only the Spanning Tree Protocol (STP) is specifically designed to prevent loops and maintain a stable Layer 2 environment. Understanding the roles of CDP, VTP, EtherChannel, and STP highlights why STP is essential for loop prevention and reliable network operation.
CDP, or Cisco Discovery Protocol, is a Layer 2 protocol that enables network devices to identify and share information with directly connected neighbours. Administrators use CDP to map network topology, verify connections, and troubleshoot misconfigurations. While CDP is valuable for visibility and documentation, it does not address the risk of loops or broadcast storms within the network. It provides no mechanism for controlling traffic flow or maintaining a loop-free topology, leaving networks vulnerable if redundant links exist.
VTP, or VLAN Trunking Protocol, serves a different purpose, synchronising VLAN configuration across multiple switches in a domain. VTP simplifies management by propagating VLAN changes from a central switch to other switches, ensuring consistent configuration and reducing administrative overhead. However, VTP does not prevent Layer 2 loops or mitigate broadcast storms. While it is critical for consistent VLAN management, it does not influence how frames traverse redundant paths or prevent network instability caused by looping traffic.
EtherChannel is another technology that improves network performance and redundancy. By bundling multiple physical links into a single logical link, EtherChannel increases bandwidth and provides failover if one member link fails. While EtherChannel enhances throughput and provides link-level redundancy, it does not inherently prevent loops. If redundant paths exist outside of the EtherChannel bundle, the network is still susceptible to looping frames and broadcast storms unless a protocol like STP is implemented.
STP, or Spanning Tree Protocol, is specifically designed to address these issues in Layer 2 networks. In a topology with redundant links, frames can circulate endlessly if a loop exists, generating broadcast storms that overwhelm network resources and destabilise the network. STP prevents this by logically blocking redundant paths while allowing at least one active path between switches. STP elects a root bridge based on bridge priority and MAC addresses, and assigns roles to each port, including root ports, designated ports, and blocked ports. This ensures that only loop-free paths are active for forwarding traffic.
One of the key benefits of STP is that it allows network redundancy without sacrificing stability. If an active link fails, STP recalculates the topology and activates previously blocked ports to maintain connectivity. This dynamic recalculation ensures continuous network operation while preventing loops. Rapid Spanning Tree Protocol (RSTP) enhances STP by improving convergence times, minimising downtime during topology changes, and ensuring that network services remain available even in the event of link failures.
STP is critical for designing reliable Layer 2 networks in enterprise environments. It allows administrators to implement redundant topologies, increasing resilience, while ensuring that broadcast storms and loops do not disrupt operations. By maintaining a loop-free logical topology, STP provides predictable and stable network performance, supporting mission-critical applications and reducing troubleshooting complexity.
While CDP helps discover neighbouring devices, synchronises VLAN configurations, and EtherChannel provides link aggregation and redundancy, only STP directly addresses the issue of loops and broadcast storms. By blocking redundant paths, dynamically recalculating the topology in case of failures, and supporting rapid convergence, STP ensures a stable and reliable Layer 2 network. Therefore, STP is the essential protocol for preventing loops, maintaining network stability, and supporting high availability in enterprise switch environments.
Question 75
Which NAT mechanism allows many internal hosts to share a single public IP address using unique port numbers?
A) Static NAT
B) Dynamic NAT
C) PAT
D) NAT64
Answer: C) PAT
Explanation:
In modern network environments, translating private IP addresses to public addresses is a fundamental task that allows devices on internal networks to communicate with external networks, including the Internet. There are several approaches to performing this translation, each with unique benefits and limitations, such as static NAT, dynamic NAT, NAT64, and Port Address Translation (PAT). Understanding the differences among these methods highlights why PAT is the most effective solution for allowing multiple devices to share a single public IP while maintaining reliable connectivity and efficient resource utilisation.
Static NAT is a method in which a specific private IP address is permanently mapped to a single public IP address. This approach is often used for servers or services that must be accessible from the Internet, such as web servers, email servers, or VPN gateways. Static NAT ensures that these devices are consistently reachable at a known public address. While this method is straightforward and reliable for individual devices, it does not scale well for larger networks because each private host requires a dedicated public IP. As a result, static NAT cannot support multiple internal devices sharing a single public IP, making it unsuitable for environments where public IP resources are limited.
Dynamic NAT improves flexibility by using a pool of public IP addresses that can be assigned to internal devices on a one-to-one basis. When an internal device initiates communication with an external network, it is temporarily assigned an available public IP from the pool. While dynamic NAT is more efficient than static NAT in terms of public IP usage, it still maintains a strict one-to-one relationship. Once the pool of public IPs is exhausted, additional internal devices cannot access external resources until an address becomes available. This limitation makes dynamic NAT less suitable for networks with a large number of internal hosts requiring simultaneous external access.
NAT64 is a specialised translation technique used in networks transitioning from IPv4 to IPv6. It allows IPv6-only devices to communicate with IPv4 networks by translating IPv6 addresses into IPv4 addresses and vice versa. While NAT64 is critical for IPv6/IPv4 interoperability, it does not address the challenge of multiple IPv4 devices sharing a single public IP. NAT64 is primarily concerned with protocol translation rather than efficient address conservation for multiple hosts.
Port Address Translation, commonly known as PAT or NAT overload, solves these challenges effectively by allowing multiple internal devices to share a single public IP address. PAT works by assigning a unique port number to each session initiated by an internal device. The router maintains a translation table that maps each internal IP and port combination to a corresponding public port number. This ensures that return traffic is routed correctly to the originating internal device, even when multiple hosts are accessing external networks simultaneously.
PAT offers several advantages that make it widely used in enterprise, data centre, and home networks. First, it conserves public IP addresses by enabling many devices to share a single public address. This is particularly important given the limited availability of IPv4 addresses. Second, it supports a large number of simultaneous connections, allowing multiple users or applications to communicate externally without requiring additional public IPs. Third, it simplifies network management by centralising external connectivity through a single public interface while maintaining session integrity for each internal host.
In practice, PAT allows internal networks to connect to the Internet efficiently and securely. Each session is uniquely identified by the combination of internal IP, internal port, and assigned external port, allowing routers to handle thousands of concurrent connections reliably. This mechanism reduces administrative overhead, conserves address space, and ensures seamless connectivity for end-users.
While static NAT provides dedicated mappings for individual hosts, dynamic NAT uses a pool of addresses but still maintains one-to-one mappings, and NAT64 facilitates IPv6-to-IPv4 translation; only PAT allows multiple internal hosts to share a single public IP effectively. By mapping internal IPs to unique external ports, PAT ensures proper session routing, optimises the use of public address resources, and supports scalable, efficient network connectivity. Therefore, PAT is the preferred method for networks requiring multiple internal devices to access external resources simultaneously while conserving public IP addresses.