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Q361. Which OSPF parameter is used to identify a router uniquely within an OSPF routing domain?

1) Router ID
2) Area ID
3) Process ID
4) Network ID

Correct Answer: 1) Router ID

Explanation:
The OSPF Router ID uniquely identifies an OSPF router within an OSPF routing domain. It is a 32-bit value normally selected from an explicitly configured router ID, the highest IP address on a loopback interface, or the highest active physical interface address if no loopback exists. The Router ID is used in OSPF neighbor relationships, LSAs, and the SPF calculation. It is important because duplicate Router IDs can cause serious OSPF problems, including unstable adjacencies and incorrect link-state information. The OSPF process ID configured with the router ospf command is locally significant and does not identify the router to other OSPF devices. Therefore, the Router ID is the correct parameter.

Q362. Two OSPF routers fail to establish an adjacency because their Hello intervals are different. What should be done?

1) Change the OSPF router IDs
2) Configure matching Hello intervals
3) Increase the OSPF reference bandwidth
4) Enable route redistribution

Correct Answer: 2) Configure matching Hello intervals

Explanation:
OSPF neighbors on the same network segment must agree on several parameters before they can form a stable adjacency. The Hello interval is one of these important parameters. If one router sends Hello packets every 10 seconds while another expects them every 30 seconds, the routers will reject the neighbor relationship because their OSPF parameters do not match. The Hello interval should therefore be configured consistently on both sides. The dead interval should also normally match because it determines how long a router waits before declaring a neighbor unreachable. Router IDs and reference bandwidth do not directly resolve a Hello timer mismatch. Correctly matching the OSPF Hello configuration allows the routers to establish adjacency.

Q363. Which OSPF feature can reduce the impact of frequent topology changes by controlling the timing of SPF calculations?

1) OSPF passive interfaces
2) OSPF route summarization
3) SPF throttling
4) OSPF stub areas

Correct Answer: 3) SPF throttling

Explanation:
OSPF SPF throttling controls how frequently the Shortest Path First algorithm is recalculated after topology changes. In a network experiencing frequent link-state changes, immediately running SPF after every individual event can consume significant CPU resources. SPF throttling introduces controlled delays between topology changes and SPF calculations, allowing multiple changes to be processed more efficiently. This can improve router stability in networks where routing information changes frequently. Route summarization reduces the number of routes advertised between areas, while stub areas reduce external route information, but neither directly controls the timing of SPF calculations. Passive interfaces prevent OSPF neighbor formation on selected interfaces. Therefore, SPF throttling is specifically designed to manage the frequency of SPF calculations.

Q364. Which technology can be used to detect an OSPF link failure faster than waiting for standard OSPF dead timers?

1) BFD
2) NAT
3) DHCP
4) NTP

Correct Answer: 1) BFD

Explanation:
Bidirectional Forwarding Detection, or BFD, provides rapid detection of forwarding-path failures. OSPF normally depends on Hello and Dead intervals to determine whether a neighbor is still reachable. Depending on the configured timers, this can take several seconds. BFD can operate with much shorter detection intervals and notify the routing protocol when a forwarding path fails. OSPF can then quickly remove the affected neighbor and recalculate routes. BFD is particularly useful in environments where fast convergence is important, such as enterprise WANs and service-provider networks. NAT translates addresses, DHCP provides address configuration, and NTP synchronizes clocks. None of these protocols is designed to provide rapid routing-path failure detection.

Q365. In EIGRP named mode, where are interface-specific EIGRP settings normally configured?

1) Under the global router eigrp configuration only
2) Under the address-family configuration only
3) Under the interface configuration directly without an EIGRP address family
4) Under the EIGRP address-family interface configuration

Correct Answer: 4) Under the EIGRP address-family interface configuration

Explanation:
EIGRP named mode provides a structured configuration hierarchy that differs from classic EIGRP configuration. Within named EIGRP, an address-family is created, and interface-specific settings are configured under the appropriate address-family interface section. This organization makes the configuration easier to manage and provides additional flexibility for EIGRP features. Depending on the IOS version and configuration, commands can be applied under sections such as af-interface. Examples of settings that can be configured there include authentication, passive-interface behavior, hello-related settings, and other interface-level EIGRP parameters. Simply placing all settings under the global router eigrp section is not the correct approach for interface-specific named-mode configuration.

Q366. Which EIGRP feature allows routes to be identified with a tag so that routing policies can be applied later?

1) Route tagging
2) Variance
3) Split horizon
4) Feasibility condition

Correct Answer: 1) Route tagging

Explanation:
EIGRP route tagging allows a routing administrator to associate identifying information with routes as they are redistributed or processed. Route tags are especially useful in complex networks where routes may travel through multiple routing domains. A route can be tagged when it enters a routing protocol and later matched using a route map or routing policy. This helps prevent routing loops and allows administrators to control which routes should be redistributed into another protocol. Variance controls unequal-cost load balancing, while split horizon helps prevent routing loops by restricting advertisements back through the interface from which they were learned. The feasibility condition determines whether an EIGRP path can qualify as a feasible successor. Therefore, route tagging is the appropriate feature.

Q367. What happens when an EIGRP summary route is configured on an interface?

1) EIGRP disables all routing advertisements
2) The router creates a summary route pointing to Null0
3) The router automatically converts all routes to external routes
4) The router removes the EIGRP topology table

Correct Answer: 2) The router creates a summary route pointing to Null0

Explanation:
When EIGRP manual summarization is configured on an interface, the router generally creates a summary route pointing toward Null0. This behavior prevents routing loops and prevents packets destined for an address within the summary range, but not matching a more specific route, from being forwarded incorrectly. The Null0 route acts as a discard route for unmatched destinations inside the summary. EIGRP then advertises the summary rather than advertising every individual component route across the relevant interface. This can reduce routing-table size and limit the propagation of detailed topology information. Manual summarization can therefore improve scalability while also providing a useful boundary for routing information. The other options do not describe normal EIGRP summarization behavior.

Q368. Which BGP attribute is considered when selecting between paths after higher-priority attributes such as weight and local preference?

1) Router ID
2) Origin code
3) AS_PATH
4) MED

Correct Answer: 3) AS_PATH

Explanation:
BGP uses a defined best-path selection process that evaluates multiple attributes in sequence. On Cisco devices, locally significant weight is considered first, followed by Local Preference and other attributes before AS_PATH is evaluated. In general, when comparing otherwise suitable paths, BGP prefers the path with the shorter AS_PATH. AS_PATH represents the autonomous systems through which the route advertisement has traveled. A shorter path is normally considered preferable because it represents fewer AS hops. Origin code and MED are evaluated later in the selection process, while the Router ID is used toward the end as a tie-breaker. Understanding the order of BGP path attributes is essential when troubleshooting why one route is preferred over another.

Q369. An administrator wants to influence inbound traffic by making routes advertised to an external BGP neighbor appear less attractive. Which technique can be used?

1) AS-path prepending
2) Increasing local preference
3) Increasing the BGP weight
4) Changing the router ID

Correct Answer: 1) AS-path prepending

Explanation:
AS-path prepending is commonly used to influence inbound traffic entering an autonomous system. The administrator can artificially add the local AS number multiple times to the AS_PATH of selected outbound route advertisements. When another autonomous system receives multiple paths to the same destination, the path containing the longer AS_PATH is generally less preferred than a path with a shorter AS_PATH, assuming relevant earlier attributes are equal. This technique can make one link less attractive for incoming traffic. Local Preference and Weight primarily influence outbound path selection within the local autonomous system rather than directly influencing how external networks choose inbound paths. Router ID does not provide a normal mechanism for controlling inbound traffic flow.

Q370. Which BGP feature allows multiple neighbors to inherit common configuration settings?

1) Route reflector
2) Peer group
3) Confederation
4) Route dampening

Correct Answer: 2) Peer group

Explanation:
A BGP peer group allows multiple BGP neighbors to share common configuration parameters. This can simplify administration and reduce repetitive configuration, especially when many neighbors have similar policies. Instead of configuring identical settings individually for every neighbor, the administrator can place common parameters into a peer group and associate neighbors with it. Peer groups can improve configuration consistency and can also reduce the processing required for repeated outbound policy calculations in supported implementations. A route reflector is used to reduce the need for a full mesh of iBGP sessions. Confederations divide an autonomous system into internal sub-autonomous systems for BGP scaling. Route dampening is designed to suppress unstable routes. Therefore, peer groups are the correct choice.

Q371. Which BGP attribute is primarily used to influence outbound traffic selection within an autonomous system and is propagated to iBGP peers?

1) MED
2) Local Preference
3) AS_PATH
4) Origin

Correct Answer: 2) Local Preference

Explanation:
BGP Local Preference is used to influence which exit path routers within an autonomous system should use to reach external destinations. A higher Local Preference value is preferred. Unlike Weight, which is a Cisco-local attribute and is not propagated to BGP peers, Local Preference is advertised to other iBGP routers within the autonomous system. This allows an organization to consistently influence outbound traffic across multiple internal routers. For example, an administrator can assign a higher Local Preference to routes learned through a preferred Internet connection. MED can influence which external entry point another autonomous system selects, while AS_PATH and Origin have different roles in BGP path selection. Therefore, Local Preference is the correct attribute.

Q372. In an MPLS Layer 3 VPN, which device typically adds the VPN label that identifies the appropriate VRF or service path?

1) Customer router
2) Provider core P router
3) PE router
4) Internet DNS server

Correct Answer: 3) PE router

Explanation:
In an MPLS Layer 3 VPN, the Provider Edge, or PE, router connects directly to customer networks and maintains separate VRFs for different VPN customers. When traffic enters the MPLS VPN through a PE router, the PE determines the appropriate VPN route and label information. MPLS packets commonly use a label stack, where one label helps transport the packet across the provider network and another label identifies the VPN service or egress PE. Core P routers generally perform label switching without maintaining customer VRF information. Customer routers normally send ordinary IP packets toward the PE and do not participate directly in the provider’s MPLS label-switched core. Therefore, the PE router is responsible for assigning the VPN-related label.

Q373. What is the primary purpose of LDP discovery in an MPLS network?

1) To exchange customer VPN routes
2) To discover neighboring LDP-enabled routers
3) To assign IP addresses to PE routers
4) To encrypt MPLS traffic

Correct Answer: 2) To discover neighboring LDP-enabled routers

Explanation:
Label Distribution Protocol discovery allows MPLS routers to identify neighboring routers that are capable of participating in LDP. LDP discovery commonly uses UDP Hello messages to announce the presence of an LDP-enabled router and identify potential LDP neighbors. After discovery, routers establish an LDP session, typically using TCP, to exchange label bindings and other information required for label distribution. This distinction between discovery and session establishment is important when troubleshooting MPLS. LDP does not exchange customer VPN routes; MP-BGP is commonly used for VPN route distribution. LDP also does not provide encryption or IP address assignment. Its primary role is to establish awareness of neighboring LDP speakers before label-binding exchange occurs.

Q374. What is the main purpose of the MPLS label stack in an MPLS Layer 3 VPN?

1) To identify the physical interface only
2) To provide wireless authentication
3) To carry both transport and VPN forwarding information
4) To replace all routing protocols

Correct Answer: 3) To carry both transport and VPN forwarding information

Explanation:
MPLS Layer 3 VPN traffic commonly uses a two-label stack. The outer label is generally used to transport the packet across the MPLS provider core toward the appropriate PE router. The inner label identifies the VPN or forwarding context at the destination PE, allowing the PE to place the packet into the correct VRF. This separation enables the provider core to switch packets without needing customer-specific routing tables. MPLS labels do not replace routing protocols; routing protocols are still required to establish reachability and distribute information. The label stack also does not provide encryption or wireless authentication. Understanding the roles of the transport and VPN labels is essential for troubleshooting MPLS VPN forwarding.

Q375. Which command is most useful for verifying the IPsec security associations and packet counters on a Cisco router?

1) show ip route
2) show crypto ipsec sa
3) show ip ospf neighbor
4) show interfaces description

Correct Answer: 2) show crypto ipsec sa

Explanation:
The show crypto ipsec sa command provides detailed information about active IPsec Security Associations. It can display encryption and authentication parameters, peer information, SPI values, encapsulation and decapsulation counters, and other information useful for troubleshooting IPsec tunnels. Packet counters are particularly valuable because they can help determine whether traffic is actually being encrypted and decrypted. For example, increasing encapsulation counters indicate that traffic is being protected by the IPsec policy, while increasing decapsulation counters indicate that encrypted traffic is being received and processed. show ip route is useful for routing information, while show ip ospf neighbor verifies OSPF relationships. Therefore, show crypto ipsec sa is the most appropriate command.

Q376. Which IPsec component defines the algorithms and parameters used to protect IPsec traffic?

1) Transform set
2) Route map
3) DHCP pool
4) NHRP network ID

Correct Answer: 1) Transform set

Explanation:
An IPsec transform set defines the security algorithms and protocols used to protect traffic. Depending on the configuration, a transform set can specify encryption and authentication or integrity mechanisms used by IPsec. It is associated with the IPsec policy so that matching traffic can be protected using the defined parameters. Modern configurations may use stronger combinations of encryption and integrity mechanisms, while older configurations can use protocols such as ESP with specific encryption algorithms. A route map is used for policy-based routing, redistribution, or other routing-policy functions. DHCP pools assign IP addressing information, and NHRP parameters are associated with technologies such as DMVPN. Therefore, the transform set is the component that specifies IPsec protection parameters.

Q377. Which QoS mechanism can drop lower-priority packets before a queue becomes completely full, helping reduce congestion effects?

1) LLQ
2) CBWFQ
3) WRED
4) Policing

Correct Answer: 3) WRED

Explanation:
Weighted Random Early Detection, or WRED, is a congestion-avoidance mechanism that can begin dropping packets before a queue reaches its maximum capacity. By selectively dropping packets based on queue thresholds and, in some configurations, packet markings such as IP precedence or DSCP, WRED attempts to avoid sudden queue overflow. This behavior can help reduce the likelihood of widespread packet loss when congestion occurs. Low Latency Queuing provides strict priority treatment for delay-sensitive traffic. CBWFQ allocates bandwidth among defined traffic classes, while policing limits traffic rates and can drop or remark traffic when configured thresholds are exceeded. WRED is therefore specifically associated with early packet dropping as congestion increases.

Q378. Which IPv6 mechanism allows a host to obtain an address and gateway information through router advertisements while using DHCPv6 only for additional information?

1) Stateful DHCPv6
2) Stateless DHCPv6
3) NAT64
4) IPv6 tunneling

Correct Answer: 2) Stateless DHCPv6

Explanation:
Stateless DHCPv6 allows IPv6 hosts to use Router Advertisements and SLAAC to generate their IPv6 addresses while obtaining additional configuration information from a DHCPv6 server. Router Advertisements can indicate that hosts should use SLAAC for address configuration and may also indicate that DHCPv6 should be used for supplementary parameters such as DNS-related information. In contrast, stateful DHCPv6 provides addresses directly from a DHCPv6 server. NAT64 is used to facilitate communication between IPv6 and IPv4 environments, while IPv6 tunneling carries IPv6 traffic across networks that may not natively support IPv6. Therefore, stateless DHCPv6 is the appropriate mechanism when SLAAC provides addressing and DHCPv6 supplies additional parameters.

Q379. Which IP SLA operation is most appropriate for measuring delay, jitter, packet loss, and response-time variation for voice-like traffic?

1) ICMP echo
2) DNS operation
3) HTTP operation
4) UDP jitter

Correct Answer: 4) UDP jitter

Explanation:
The IP SLA UDP jitter operation is designed to measure characteristics that are especially relevant to real-time applications such as voice and video. It can provide information about round-trip delay, one-way or two-way delay depending on configuration, packet loss, and variations in packet arrival times commonly referred to as jitter. These measurements help administrators evaluate whether a network path can support delay-sensitive applications. An ICMP echo operation primarily measures reachability and round-trip response time. DNS and HTTP operations test application-specific services but do not provide the same detailed jitter measurements. Therefore, UDP jitter is the most suitable IP SLA operation for analyzing network performance characteristics associated with real-time traffic.

Q380. Which command provides a concise overview of the routes installed in the IPv4 routing table on a Cisco router?

1) show ip route
2) show ip protocols
3) show arp
4) show cdp neighbors

Correct Answer: 1) show ip route

Explanation:
The show ip route command displays the IPv4 routing table and is one of the most important commands for troubleshooting routing problems on Cisco routers. It shows connected, static, and dynamically learned routes, along with route codes, next-hop information, outgoing interfaces, administrative distance, and metric information. Administrators can use the command to determine whether a destination is reachable and which path the router intends to use. show ip protocols provides information about routing protocols and their configuration, but it does not display the complete routing table. show arp displays IPv4-to-MAC address mappings, while show cdp neighbors identifies directly connected Cisco devices. Thus, show ip route is the correct command for examining installed IPv4 routes.