Implementing Cisco Service Provider Advanced Routing Solutions (SPRI) Free Practice Test — 30 Questions

Question 1

A large telecommunications provider is experiencing significant customer complaints regarding packet loss and service degradation for a specific enterprise client. Network monitoring reveals that the Border Gateway Protocol (BGP) session with a key upstream provider is exhibiting frequent flaps. Analysis of the BGP state logs indicates that the session is being reset due to Hold Timer expiry, even though the physical link remains up and there are no reported issues with the customer\'s own network infrastructure. The engineering team has ruled out configuration errors on their edge routers and suspects intermittent packet drops or delays affecting BGP Keepalive messages between the peering routers. To restore stable connectivity for the affected customer segment, which of the following adjustments would most effectively address the Hold Timer expiry issue by increasing session resilience?

Accepted Answer

Increase the BGP Hold Timer value on the peering routers.

Question 2

Consider a scenario where a network engineer is configuring BGP peering between their service provider network and an external enterprise customer. The objective is to influence how inbound traffic from the enterprise customer is routed within the service provider\'s network, assuming all other BGP path attributes (Local Preference, AS_PATH, Origin) are equal for multiple paths learned from the same customer AS. Which BGP path attribute would the service provider primarily manipulate on their edge routers to signal a preference for a specific ingress path from the enterprise customer, thereby influencing the customer\'s outbound traffic flow towards the service provider\'s network?

Accepted Answer

Multi-Exit Discriminator (MED)

Question 3

A service provider\'s network engineering team is tasked with optimizing traffic flow to enhance customer experience and meet service level agreements (SLAs). They need to ensure that a significant portion of outbound traffic from their network is directed towards a peering partner offering high throughput and low latency. Simultaneously, they must mitigate the risk of routing specific customer traffic over a link that has exhibited intermittent packet loss, which could degrade application performance. The team is evaluating BGP path selection mechanisms to achieve these dual objectives without deploying complex overlay technologies. Which BGP attribute, when manipulated by the service provider, would most directly and effectively influence the selection of the preferred outbound path while also allowing for avoidance of the problematic link for sensitive traffic flows?

Accepted Answer

Local Preference

Question 4

A service provider, \"AetherNet Telecom,\" is experiencing suboptimal inbound traffic flow from a significant enterprise customer, \"Quantum Dynamics Inc.\" Quantum Dynamics originates its network prefixes and has connectivity to AetherNet Telecom through two separate upstream transit providers, \"GlobalConnect\" and \"HorizonLink.\" AetherNet Telecom wishes to steer Quantum Dynamics\' traffic towards its network via GlobalConnect, as GlobalConnect offers a more favorable peering agreement for this specific customer. AetherNet Telecom has established BGP peering with both GlobalConnect and HorizonLink. What is the most effective strategy for AetherNet Telecom to influence Quantum Dynamics to prefer the GlobalConnect path for traffic destined to AetherNet Telecom\'s network?

Accepted Answer

Advertise specific BGP communities on the prefixes it announces to GlobalConnect that signal a preference for traffic originating from Quantum Dynamics to ingress via GlobalConnect.

Question 5

A network engineer is designing a BGP confederation architecture for a large service provider, aiming to improve scalability and manageability. Within this design, a route reflector in Sub-AS 100 receives an external eBGP route. This route is then propagated to clients within Sub-AS 100 and subsequently advertised to Sub-AS 200 through a confederation boundary router. If the confederation boundary router does not apply the `next-hop-self` attribute to the routes being advertised to its iBGP peers in Sub-AS 200, what is the most likely consequence for route propagation between the sub-ASes?

Accepted Answer

Routes advertised to Sub-AS 200 will retain the original next-hop IP address from the route reflector client in Sub-AS 100, potentially causing reachability issues if this IP is not directly advertised or reachable within Sub-AS 200.

Question 6

A multinational telecommunications firm is experiencing intermittent route instability for a critical customer prefix originating from an external Autonomous System (AS). After confirming stable physical connectivity and successful BGP peering establishment between their edge routers and the customer\'s network, the network operations team observes that the specific customer prefix is frequently being withdrawn and then re-advertised by their internal BGP speakers. Initial troubleshooting has ruled out simple interface flaps or power issues. Which of the following scenarios is the MOST likely root cause of this BGP route flapping, considering the advanced routing solutions typically deployed in a service provider environment?

Accepted Answer

A route-map applied inbound on the BGP session is dynamically altering the `NEXT_HOP` attribute based on complex AS_PATH matching, causing the BGP speaker to lose reachability to the advertised next-hop for the specific prefix during certain path changes.

Question 7

A service provider\'s network experiences persistent instability on a critical transit link connecting to a major internet exchange point (IXP). Customers report intermittent connectivity and degraded performance due to rapid and frequent withdrawal and re-advertisement of a substantial number of BGP prefixes. Network engineers have confirmed that the BGP sessions themselves are stable in terms of reachability and basic TCP connectivity, and there are no indications of underlying physical layer issues on the link. The observed behavior is characterized by a cyclical pattern of prefixes disappearing and reappearing in the BGP routing table, impacting routing convergence and overall service availability.

Which of the following is the most probable root cause for this observed BGP route flapping behavior, considering advanced routing solutions and potential misconfigurations in a large-scale service provider environment?

Accepted Answer

Aggressively tuned BGP route dampening parameters are incorrectly suppressing and re-enabling routes, leading to the observed flapping.

Question 8

A large enterprise customer reports persistent, intermittent BGP route flapping for a substantial number of IP prefixes they originate and are advertised by your service provider\'s core network. This instability is leading to noticeable service degradations and an increase in customer support escalations. The issue appears to be systemic, affecting multiple customer-facing routers and a wide range of their advertised prefixes, rather than isolated prefix advertisements. What is the most probable root cause for this widespread BGP route instability?

Accepted Answer

Overly aggressive or misconfigured route filtering policies applied to the customer's prefixes.

Question 9

A large telecommunications provider is experiencing significant network instability, manifesting as frequent BGP route flapping from a specific upstream transit provider. This instability is causing intermittent connectivity issues for a substantial portion of their customer base, particularly impacting services that rely on low latency and consistent path availability. The network engineering team has identified that the root cause is not a hardware failure but rather a series of rapid, unannounced prefix changes from the upstream provider, likely due to their internal network dynamics. The provider\'s current BGP configuration utilizes route reflection for internal scaling and has basic prefix summarization applied at peering points. They are considering several strategies to mitigate the impact of this upstream instability. Which of the following approaches would most effectively address the immediate problem of route flapping and improve overall routing stability without sacrificing necessary reachability information?

Accepted Answer

Implement BGP dampening on inbound routes from the problematic upstream provider, carefully tuning suppression and reuse parameters to filter out transiently unstable paths.

Question 10

A service provider\'s core network is experiencing intermittent connectivity issues affecting a significant segment of its enterprise customer base. Investigation reveals that a BGP session with a key upstream transit provider is flapping frequently. This instability is causing route churn and impacting the Quality of Service for affected customers. Network engineers have confirmed that the issue originates from the upstream provider\'s network, but the service provider needs to implement internal BGP configurations to mitigate the impact on its customers while working with the upstream provider for a permanent fix. Which BGP configuration strategy, when applied to routes learned from the flapping upstream provider, would most effectively improve inbound path stability and reduce customer-facing service disruptions?

Accepted Answer

Implement a policy to set a lower `LOCAL_PREF` value for routes learned from the flapping upstream provider, ensuring that traffic is preferentially routed through other stable upstream connections.

Question 11

A service provider is experiencing intermittent route instability for a specific customer prefix. The customer utilizes a multi-homed architecture with two edge routers, each advertising the same prefix to the provider. Analysis of the BGP peering sessions reveals that the connection to one of the customer\'s edge routers is stable, while the session to the other edge router exhibits frequent resets and re-establishment, leading to the prefix becoming temporarily unavailable. What is the most likely underlying cause for this specific BGP session flapping?

Accepted Answer

Mismatched BGP timer configurations between the provider and the affected customer edge router.

Question 12

A large Tier-1 service provider is observing a persistent surge in inter-domain routing instability. Analysis of network telemetry indicates a significant increase in BGP route flaps originating from a particular set of peering sessions. These rapid state changes (up/down transitions) are causing intermittent connectivity issues for downstream customers and are straining the control plane resources of multiple core routers. The network engineering team needs to implement a proactive strategy to minimize the impact of these unstable routes without immediately disrupting established peering agreements or requiring extensive topology changes. Which advanced routing solution should be prioritized for immediate deployment to address this specific challenge?

Accepted Answer

Implement BGP route dampening with carefully tuned penalty and suppression timers.

Question 13

A service provider\'s network is experiencing intermittent connectivity issues for a critical customer prefix. Network monitoring reveals that the customer\'s edge router is frequently advertising and withdrawing this prefix, causing BGP route flaps. The provider\'s internal BGP configurations, peerings, and link health have been verified and are stable. The customer\'s network infrastructure is believed to be the source of the unpredictable prefix advertisement. Which proactive BGP policy configuration, applied to the peering session with this customer, would best mitigate the impact of these external route flaps on the provider\'s network stability without completely blocking the prefix?

Accepted Answer

Apply an inbound route-map to the customer's BGP session that permits the customer's prefix and sets a lower local preference for it.

Question 14

Consider a large Tier-1 service provider operating a multi-AS backbone. Network engineers observe that during periods of significant link instability affecting several core transit links, their BGP routing tables are exhibiting remarkably swift convergence times, even with frequent prefix state changes. This rapid adaptation occurs despite the underlying instability, which typically would lead to prolonged route flapping and slower convergence. What configuration parameter, when set to a shorter duration, most directly contributes to this observed behavior of quick recovery from transient route instability?

Accepted Answer

BGP dampening half-life

Question 15

A network operations team is troubleshooting a critical service provider backbone where two core routers, Router A and Router B, established an eBGP peering session. The session exhibits intermittent instability, cycling between the \'Established\' and \'Idle\' states, leading to unpredictable routing updates and service disruptions. Examination of router logs reveals messages indicating the BGP state change from \'Established\' to \'Idle\' and subsequent re-establishment attempts. The physical link between Router A and Router B is a direct, high-speed Ethernet connection. Considering the nature of eBGP session flapping on a direct link, which of the following underlying network conditions is most likely contributing to this persistent instability?

Accepted Answer

A mismatch in the configured or auto-negotiated interface speed and duplex settings between the directly connected ports on Router A and Router B.

Question 16

A large telecommunications provider is experiencing a degradation in service quality for customers utilizing services that traverse a key inter-AS peering connection. Network telemetry indicates a consistent increase in packet loss and elevated latency on this specific link. Analysis of BGP routing tables reveals that the current path being utilized to reach a significant destination AS is suboptimal, routing traffic through an intermediate AS that is experiencing congestion. The network engineering team needs to implement a solution to influence BGP path selection and steer traffic towards a more direct and less congested path. Which BGP attribute, when manipulated within the provider\'s AS, would most effectively address this issue for outbound traffic to the affected destination AS?

Accepted Answer

Local Preference

Question 17

A Tier-1 service provider\'s network operations center (NOC) is alerted to a widespread service degradation affecting a significant portion of its enterprise customer base. Initial diagnostics reveal intermittent connectivity issues and increased latency for services relying on specific traffic engineering paths. The engineering team has recently implemented a new policy leveraging segment routing (SR) with RSVP-TE tunnels to optimize traffic flow for premium services. However, the issue appears to be more systemic, impacting a broader set of customers than anticipated by the SR policy\'s direct scope. Further investigation uncovers that BGP route dampening parameters, configured to prevent route flapping, are actively suppressing routes that are experiencing brief, transient instability. This instability is traced back to the rapid re-convergence events triggered by the SR policy\'s dynamic path adjustments in response to minor link fluctuations. Which of the following actions is the most appropriate immediate strategic response to mitigate the widespread service degradation while maintaining long-term network stability?

Accepted Answer

Adjust BGP route dampening parameters to increase the suppress threshold and half-life, while simultaneously reviewing the SR traffic engineering policy for potential tuning to reduce re-convergence frequency during transient link events.

Question 18

A service provider network engineer is troubleshooting a persistent issue of intermittent packet loss and elevated latency on a critical MPLS backbone segment linking two key aggregation points. Control plane protocols, including BGP and OSPF, report stable adjacencies and rapid convergence times. Despite the apparent health of the routing and signaling protocols, end-to-end connectivity exhibits performance degradation. Which of the following diagnostic commands would be most instrumental in pinpointing potential anomalies within the MPLS forwarding plane that could explain these symptoms?

Accepted Answer

show mpls forwarding-table

Question 19

Consider a large service provider operating two distinct Points of Presence (PoPs) within a metropolitan area, connected to the internet via redundant peering with Autonomous System (AS) 65001. The service provider\'s internal network is represented by AS 65500. Router-A is located in PoP 1, and Router-B is in PoP 2. Management requires that a significant portion of inbound traffic originating from AS 65001 be directed towards PoP 1, specifically utilizing Router-A for ingress, to leverage specialized peering infrastructure at that location. Which BGP attribute manipulation, applied on the routes advertised by AS 65500 to AS 65001, would be the most direct and effective method to achieve this traffic engineering goal?

Accepted Answer

Advertise routes from Router-A to AS 65001 with a lower Multi-Exit Discriminator (MED) value than routes advertised from Router-B.

Question 20

A large Tier-1 service provider is experiencing intermittent route instability impacting a critical peering relationship. Network engineers have ruled out physical layer issues and standard BGP configuration errors. Analysis reveals that the route flapping is correlated with rapid, subtle fluctuations in specific interface-level attributes advertised by the peering partner, leading to frequent BGP path re-selection for a subset of prefixes. While the BGP sessions remain established, the constant churn of best paths is degrading overall network performance and predictability. Which advanced BGP configuration strategy would be most effective in mitigating this specific type of route instability without disrupting the peering relationship or significantly altering routing policy?

Accepted Answer

Implement BGP dampening on the affected prefixes to penalize routes that exhibit frequent changes in path attributes.

Question 21

A large Tier-1 service provider is observing significant instability on a key peering session with an upstream transit provider. This instability manifests as frequent BGP route flaps for a substantial number of prefixes originating from or transiting through the upstream network. The internal network engineering team has verified that their own BGP configuration and router hardware are functioning optimally and are not the source of the problem. The issue appears to stem from the upstream provider\'s network experiencing transient failures and rapid convergence events, leading to unpredictable changes in next-hop reachability for affected prefixes. This is causing increased CPU utilization on peering routers and impacting the stability of customer-facing services that rely on these routes. Considering the service provider\'s commitment to maintaining network stability and service availability, which of the following proactive measures is the most technically sound and operationally feasible approach to mitigate the impact of this external instability without disrupting legitimate traffic flows or severing the peering relationship?

Accepted Answer

Implement BGP dampening with carefully tuned suppress and reuse thresholds to penalize and temporarily suppress frequently changing routes.

Question 22

A global internet service provider, \"NebulaNet,\" is experiencing significant packet loss and increased latency on a primary inter-AS peering link connecting to a major content delivery network (CDN). This degradation is attributed to an unforeseen, massive surge in encrypted peer-to-peer file sharing traffic, a category not adequately represented in NebulaNet\'s historical traffic forecasting models. Existing traffic engineering policies, configured for predictable diurnal patterns and scheduled major events, are proving insufficient. NebulaNet\'s primary objective is to mitigate the immediate service impact on its premium subscribers, who are experiencing severe disruptions to real-time applications, without compromising the overall network stability. Which of the following strategic adjustments best embodies the principles of advanced service provider routing solutions to address this emergent situation?

Accepted Answer

Dynamically re-engineer traffic paths using Segment Routing with Traffic Engineering extensions to leverage underutilized alternative peering routes, prioritizing low-latency metrics and real-time path computation based on current link utilization and congestion levels.

Question 23

A large Tier-1 service provider is experiencing significant network instability affecting a critical enterprise customer’s connectivity. Analysis of the BGP routing tables reveals that a specific customer-advertised prefix is frequently flapping, causing intermittent reachability issues. Network engineers have confirmed that the underlying physical layer is stable, and the issue appears to stem from the dynamic nature of BGP path selection and advertisement for this prefix. The provider needs a robust solution to mitigate the impact of this unstable route without disrupting overall BGP convergence for other prefixes. Which BGP feature, when appropriately configured, would most effectively address this persistent route flapping by penalizing and temporarily suppressing routes that exhibit excessive state changes?

Accepted Answer

BGP route dampening

Question 24

A network operations team at a large Tier-1 ISP is observing persistent, intermittent instability for a critical customer prefix advertised via BGP. The prefix is frequently withdrawn and then re-advertised, leading to unpredictable path changes and impacting service continuity. The team has ruled out physical link issues and basic configuration errors on the directly connected peers. Considering the advanced routing solutions within the SPRI curriculum, which of the following strategies would most effectively address and stabilize this specific flapping prefix without introducing significant network-wide overhead or complex policy re-engineering?

Accepted Answer

Implement BGP route dampening with carefully tuned penalty and suppression thresholds.

Question 25

A service provider\'s core network is experiencing intermittent instability for a specific customer-announced prefix. BGP neighbor sessions with this customer remain in an Established state, and the provider\'s local BGP policy configurations for advertising this prefix appear correct. The instability is confined solely to this single customer prefix, with all other customer routes and provider-internal routes functioning normally. What is the most appropriate and targeted strategy for the service provider to implement to mitigate this BGP route flapping without impacting other network operations?

Accepted Answer

Apply a route-map to the import policy of the customer's prefix that enforces prefix stability criteria or applies route dampening.

Question 26

A network operations center (NOC) engineer for a major internet service provider observes a persistent and significant increase in BGP route flap statistics on the peering session with AS 65001. The monitoring tools indicate a rapid churn of thousands of prefixes originating from AS 65001, with withdrawal and re-advertisement events occurring every few minutes for the same set of prefixes. There are no corresponding interface errors, physical layer issues, or configuration changes noted on the local provider\'s BGP routers. The impact is a degradation of overall network stability and increased CPU utilization on the peering routers. Which of the following actions is the most appropriate initial step to address this situation?

Accepted Answer

Immediately contact the Network Operations Center (NOC) of AS 65001 and request an investigation into their prefix advertisement stability and potential policy misconfigurations.

Question 27

A large telecommunications provider is experiencing intermittent BGP route flapping for a critical customer prefix. Network monitoring indicates that the prefix is being advertised and withdrawn repeatedly within short intervals, causing packet loss and service degradation for the customer. Initial diagnostics confirm that the Border Gateway Protocol (BGP) peering session between the provider\'s edge router (PE1) and the customer\'s edge router (CE1) is stable, and the Intermediate System to Intermediate System (IS-IS) adjacencies within the provider\'s network are also healthy. Further investigation reveals that the customer\'s network is experiencing minor, transient link instability on their internal network, which is briefly impacting the reachability of the customer prefix. The provider\'s BGP configuration on PE1 includes route dampening parameters, but these are set with a lower suppression threshold and a shorter reuse time than typically employed for customer routes. Considering the need to maintain network stability and minimize the impact of transient customer-side issues on the provider\'s core routing, what strategic adjustment to the BGP configuration on PE1 would most effectively mitigate this route flapping while ensuring prompt convergence for genuine routing changes?

Accepted Answer

Increase the BGP route dampening suppression threshold and extend the route reuse time for the affected customer prefix.

Question 28

Anya, a network engineer for a large telecommunications provider, is investigating a critical customer complaint regarding persistent packet loss and elevated latency on services routed through a specific segment of the SP backbone. Initial diagnostics reveal no obvious BGP flapping or MPLS TE path instability. However, monitoring of the involved core router\'s interface connected to a PE router shows a high rate of input errors and discards. The interface is operationally up, but further investigation into the physical layer configuration on the core router reveals an explicit setting of \"MDI-X\" for the interface, while the connected PE router\'s interface is configured for auto-MDIX. What is the most appropriate immediate action Anya should take to rectify the situation, assuming standard cabling practices are in use?

Accepted Answer

Reconfigure the core router's interface MDI setting to "auto" to allow for proper negotiation of the physical connection.

Question 29

A service provider\'s network is experiencing sporadic instability in the BGP reachability of a critical customer prefix. Initial diagnostics confirm the customer\'s Customer Edge (CE) router is stable and not experiencing any packet loss or interface issues. The provider\'s Provider Edge (PE) routers connected to the CE are also operating normally, with no unusual CPU or memory utilization. Further investigation reveals that an inbound route-map applied to the BGP peering session with the customer\'s upstream transit provider, which is used to influence internal routing decisions, contains a specific `deny` statement for a subset of customer prefixes. This `deny` statement is periodically being evaluated in conjunction with dynamic route filtering mechanisms within the provider\'s core network. What is the most probable underlying cause of the observed route flapping for this specific customer prefix?

Accepted Answer

An internal BGP route-map policy on the provider's network is actively denying and then re-advertising the customer prefix due to dynamic policy evaluation.

Question 30

A service provider\'s core network is experiencing persistent, intermittent route flapping for a critical customer-provided prefix. This instability is causing unpredictable reachability for the customer\'s services. Initial observations indicate that the prefix is being advertised by multiple internal BGP speakers, and the flapping occurs without any apparent configuration changes on the customer\'s edge. What is the most appropriate initial course of action to diagnose and mitigate this advanced routing instability?

Accepted Answer

Investigating BGP dampening configuration on the affected BGP sessions and analyzing the history of route advertisements for the specific customer prefix across all internal BGP speakers.

Implementing Cisco Service Provider Advanced Routing Solutions (SPRI) Free Practice Test — 30 Questions

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