4A0102 AlcatelLucent Border Gateway Protocol Free Practice Test — 30 Questions

Question 1

Given Aethelred Communications\' objective to quickly stabilize reachability for $192.0.2.0/24$ by preferring a more reliable ingress path during a convergence delay, which BGP attribute manipulation would be the most effective and appropriate initial step to influence inbound traffic, demonstrating both problem-solving abilities and adaptability to changing network conditions?

Accepted Answer

Increase the local preference on BGP sessions receiving $192.0.2.0/24$ from stable upstream providers.

Question 2

A network engineer is configuring BGP on an Alcatel-Lucent SR OS router to establish peering with both an internal iBGP peer and an external eBGP peer. After establishing the peering with the internal peer, routes are correctly learned and advertised within the internal network. However, when the router advertises routes learned from the internal peer to the external eBGP peer, the external peer receives these routes with an unreachable next-hop IP address, leading to a loss of connectivity for those prefixes. The engineer had previously applied a `next-hop-self` command on the outbound direction of the peering session with the internal iBGP peer. What is the most effective corrective action to ensure reachability for routes learned from the internal AS and advertised to the external AS?

Accepted Answer

Apply the `next-hop-self` command to the outbound direction of the peering session with the external eBGP peer.

Question 3

A telecommunications network operator, bound by stringent Service Level Agreements for real-time voice services, is experiencing intermittent congestion affecting call quality. Concurrently, the network is undergoing significant infrastructure upgrades, necessitating the integration of a new AS peering partner with distinct routing preferences. The network administrator must implement a BGP strategy that prioritizes voice traffic, dynamically discourages non-critical data during congestion, and remains robust amidst these ongoing changes. Which BGP attribute manipulation strategy, considering the need for adaptability and adherence to potential regulatory transparency requirements, would best address these multifaceted challenges on Alcatel-Lucent platforms?

Accepted Answer

Utilize BGP communities to tag traffic types and dynamically adjust local preference and MED values based on real-time network load indicators and peering agreements to steer traffic appropriately.

Question 4

An enterprise network architect is tasked with directing inbound traffic destined for their Autonomous System (AS) away from a specific peering link that is experiencing intermittent congestion. They want to make this congested link appear less attractive to external BGP speakers advertising paths into their network. Considering the standard BGP path selection process and the attributes that external BGP speakers prioritize, which of the following actions would most effectively achieve this objective without requiring direct configuration on the external peers?

Accepted Answer

Prepending the local AS number multiple times in the AS_PATH attribute of routes advertised to the peer connected via the congested link.

Question 5

Consider a scenario where an Alcatel-Lucent router receives two distinct BGP paths for the same destination prefix. Path A has a `LOCAL_PREF` value of 100, while Path B has no `LOCAL_PREF` attribute set. Both paths have an `AS_PATH` length of 5. Which attribute, or combination of attributes, would a standard Alcatel-Lucent implementation prioritize to select the best path, assuming no other explicit policy configurations like `weight` or `community` attributes are influencing the decision?

Accepted Answer

The numerically lowest neighbor IP address

Question 6

A network administrator for a large service provider, tasked with optimizing traffic flow across their global backbone using Alcatel-Lucent SR OS, is examining BGP routing tables. The provider\'s network is configured with multiple redundant paths to a specific customer network prefix, 192.168.1.0/24. The administrator observes the following BGP attributes for routes to this prefix learned from three different internal routers (Router A, Router B, and Router C) within the same Autonomous System:

*   **Router A:** Weight: 400, Local Preference: 100, AS-Path: 65001, Origin: i
*   **Router B:** Weight: 300, Local Preference: 100, AS-Path: 65002 65003, Origin: i
*   **Router C:** Weight: 200, Local Preference: 100, AS-Path: 65004, Origin: e

Considering the standard BGP path selection algorithm as implemented in SR OS, which path will the router select as the best path to reach 192.168.1.0/24?

Accepted Answer

The path learned from Router A

Question 7

An Alcatel-Lucent router has learned multiple paths to the 192.168.1.0/24 prefix from its BGP neighbors. Path A is advertised with a Local Preference of 150, an AS_PATH attribute of {AS200, AS300}, and an Origin attribute of IGP. Path B is advertised with a Local Preference of 100, an AS_PATH attribute of {AS200, AS300, AS400}, and an Origin attribute of IGP. Path C is advertised with a Local Preference of 150, an AS_PATH attribute of {AS200, AS300}, and an Origin attribute of Incomplete. Based on the BGP path selection algorithm, which path will be chosen as the best path to the 192.168.1.0/24 prefix?

Accepted Answer

Path A

Question 8

Consider a network administrator for a large enterprise that utilizes Alcatel-Lucent routers. The network has multiple redundant paths to a critical external service provider\'s network. The administrator needs to influence which of these paths their BGP-speaking routers prefer for outbound traffic to this provider, without relying on external factors like AS_PATH length or neighbor IP addresses. Which BGP attribute would the administrator most directly manipulate on their routers to enforce this preference, ensuring that the decision is primarily made within their own Autonomous System before considering external path characteristics?

Accepted Answer

Local Preference

Question 9

A network engineer is tasked with optimizing outbound traffic flow from their Alcatel-Lucent Service Router (SR) to a specific external peer. The objective is to steer traffic towards a particular path that is known to experience lower latency and less congestion, even if it involves a slightly longer AS_PATH. The engineer needs to select the most effective BGP attribute to influence this outbound path selection without impacting inbound traffic to their Autonomous System.

Accepted Answer

Local Preference

Question 10

An Alcatel-Lucent router, participating in BGP, has learned three distinct paths to the network prefix $192.168.1.0/24$. The router\'s BGP table displays the following information for each path:\n\nPath 1: AS_PATH: $65001\;65002\;65003$, Origin: IGP, Local Preference: 150, MED: 100\nPath 2: AS_PATH: $65001\;65002$, Origin: IGP, Local Preference: 100, MED: 200\nPath 3: AS_PATH: $65001\;65004\;65005$, Origin: IGP, Local Preference: 150, MED: 50\n\nBased on the standard BGP path selection algorithm, which path will the Alcatel-Lucent router install in its routing table as the best path to reach $192.168.1.0/24$?

Accepted Answer

Path 3

Question 11

An Alcatel-Lucent service router, configured for BGP peering with an external Autonomous System, is exhibiting erratic behavior where a specific customer-advertised prefix is intermittently withdrawn and then re-advertised to the BGP peer. Network monitoring indicates that the underlying IGP path to the next-hop for this prefix remains stable. Analysis of the BGP session details reveals no explicit error messages related to session establishment or hold timers. The operational team suspects a policy-driven instability. Which of the following dynamic attribute modifications is the most probable cause for this observed route flapping originating from the service router\'s advertisements?

Accepted Answer

Intermittent adjustments to the AS_PATH attribute via route-map policies triggered by external performance monitoring data.

Question 12

Consider a network administrator for a large enterprise that peers with multiple Internet Service Providers (ISPs) and has direct peering arrangements with several major content providers. The organization needs to ensure that outbound traffic destined for a specific partner network, identified as AS 65001, preferentially utilizes a path through ISP A. Concurrently, the administrator wishes to minimize the utilization of routes learned from a particular upstream provider, designated as Peer X, due to recent instability and performance degradation. Which BGP configuration strategy most effectively addresses both objectives simultaneously within the Alcatel-Lucent SR OS environment?

Accepted Answer

Apply a route-map to inbound BGP updates from Peer X, setting a low LOCAL_PREF value (e.g., 50), and apply a separate route-map to inbound BGP updates from AS 65001 (or paths containing AS 65001), setting a high LOCAL_PREF value (e.g., 200), while ensuring ISP A's routes to AS 65001 are favorably influenced by other means if necessary.

Question 13

Anya, a network engineer for a large ISP, is troubleshooting a critical BGP peering session with a major enterprise customer. The customer\'s network is experiencing intermittent route flaps originating from a specific Autonomous System (AS) on their internal network, leading to unpredictable service disruptions for their downstream clients. Anya suspects the issue might stem from instability within the customer\'s AS or their upstream connectivity, but the exact cause remains elusive due to the complexity of the multi-vendor environment and the intermittent nature of the problem. Anya needs to maintain service stability while diagnosing the root cause, requiring her to adapt her approach as new information becomes available and potentially pivot her troubleshooting focus between her own network\'s configuration, the customer\'s network, and intermediate transit providers. Which of the following best describes Anya\'s most effective approach to managing this situation, focusing on her behavioral competencies of adaptability, flexibility, and problem-solving in a dynamic BGP context?

Accepted Answer

Leveraging BGP's inherent mechanisms for route stability and dynamic path re-evaluation to understand how the protocol handles unstable advertisements and adapt troubleshooting strategies accordingly.

Question 14

An enterprise network operating AS 65000 has established BGP peering with AS 65001 and AS 65003. The network administrator wishes to influence outbound traffic destined for prefixes within AS 65001, ensuring that these prefixes are advertised to AS 65003 with a lower preference. Concurrently, the administrator wants to prevent AS 65003 from learning about these routes from AS 65000 if they were originally learned from AS 65001, thereby avoiding a potential suboptimal transit path. Which BGP attribute manipulation strategy, applied on routes learned from AS 65001, would best achieve the goal of making them less desirable for AS 65003 to use as a transit path while still allowing traffic to flow towards AS 65001 from AS 65000?

Accepted Answer

Set a lower LOCAL_PREF on routes originating from AS 65001 when advertising them to AS 65003.

Question 15

An enterprise network operating AS 65001 relies on two upstream providers, AS 65002 and AS 65003, for internet connectivity. Network engineers have observed that traffic originating from their AS is disproportionately flowing through AS 65003, leading to congestion on that link. The goal is to shift a significant portion of the inbound traffic from AS 65002 to AS 65003 without altering the existing outbound traffic engineering policies. Considering the standard BGP path selection process and typical Alcatel-Lucent (Nokia) implementation nuances, which BGP attribute manipulation would most effectively achieve this objective while maintaining operational flexibility and avoiding unintended consequences on outbound routing?

Accepted Answer

Increase the Local Preference for BGP routes learned from AS 65002.

Question 16

A network operations team is tasked with resolving a BGP peering issue between their organization\'s Alcatel-Lucent SR OS router and a new service provider\'s network. The problem manifests as specific prefixes that should be advertised to the service provider are not appearing in the provider\'s routing table, and initial checks of standard routing tables do not reveal an obvious cause. The team suspects that BGP attribute manipulation or policy-based filtering on the SR OS platform might be preventing the correct advertisement. Which diagnostic approach would most effectively help pinpoint the specific BGP attributes or policies influencing this non-advertisement on the SR OS device?

Accepted Answer

Examining the detailed BGP attributes of the affected prefixes within the local SR OS router's BGP table to identify any discrepancies or unexpected values that might be causing the issue.

Question 17

An engineer is configuring BGP peering between an Alcatel-Lucent Service Router and a third-party router from a different vendor. The goal is to influence the outbound path selection for a specific customer prefix advertised by the third-party router. The engineer configures the third-party router to set the `LOCAL_PREF` attribute to a high value for this prefix. However, upon verification, the Alcatel-Lucent router exhibits route flapping for this prefix, and the intended path selection is not consistently observed. Considering the standard BGP attribute behavior and vendor implementations, what is the most probable underlying cause of this instability and inconsistent path selection?

Accepted Answer

The Alcatel-Lucent router is ignoring the `LOCAL_PREF` attribute as it is a Cisco-proprietary attribute not universally interpreted for inbound path selection by all vendors, leading to unpredictable path selection based on other attributes or default behavior.

Question 18

A network engineer managing a large service provider network utilizing Alcatel-Lucent routing platforms is responsible for optimizing inbound traffic flow to their Autonomous System (AS) 64500. They observe that traffic from AS 65001 predominantly utilizes a suboptimal path, while traffic from AS 65002 is being directed towards a less desirable entry point. The engineer aims to influence the path selection of these external ASes to favor a specific peering point for AS 65001 and a different peering point for AS 65002, without altering the AS\'s own outbound routing preferences. Which BGP attribute manipulation strategy would be most effective for achieving this inbound traffic engineering goal, considering the principles of external BGP path selection?

Accepted Answer

Advertise the network prefixes to AS 65001 with a higher Multi-Exit Discriminator (MED) value and to AS 65002 with a lower MED value.

Question 19

Consider a network administrator configuring BGP on an Alcatel-Lucent router. Two distinct paths are advertised for the same destination prefix. Path A is received with a Local Preference of 150 and an AS_PATH length of 3. Path B is received with a Local Preference of 100 and an AS_PATH length of 2. Which path will the router select, and why does this attribute take precedence in the path selection process?

Accepted Answer

Path A will be selected because a higher Local Preference is always preferred over a shorter AS_PATH length.

Question 20

A network administrator is meticulously configuring BGP policies on an Alcatel-Lucent router to influence traffic engineering. They have established a higher local preference for a specific inbound route learned from an external peer to encourage outbound traffic to traverse a particular path. Concurrently, they have set a lower Multi-Exit Discriminator (MED) on an inbound route received from a different external peer, aiming to make their network a more attractive destination for inbound traffic from that peer. Considering these configurations and the standard BGP best path selection algorithm, what is the most likely outcome regarding path selection if the AS_PATH lengths for these two potential routes are identical and all other attributes are equal or not configured to influence the decision?

Accepted Answer

The route with the higher configured local preference will be selected as the best path for outbound traffic.

Question 21

Quantum Leap Networks (AS 65001) has established eBGP peering with two Internet Service Providers, Alpha (AS 65002) and Beta (AS 65003), to provide redundant internet connectivity. The organization advertises its /24 network prefix to both ISPs. From ISP Alpha, two distinct paths are learned for a specific external destination prefix: Path 1 has an AS path of 65002 65001 with a received MED of 100, and Path 2 has an AS path of 65002 65001 with a received MED of 150. From ISP Beta, a single path is learned with an AS path of 65003 65001 and a received MED of 50. To ensure inbound traffic to Quantum Leap Networks\' prefix is primarily directed through ISP Alpha, and to favor the more optimal ingress point from Alpha, the network administrator configures a local preference of 200 for all routes learned from ISP Alpha, while routes from ISP Beta retain the default local preference of 100. Given these configurations and the BGP path selection algorithm, which path will ultimately be chosen as the best path for the destination prefix?

Accepted Answer

Path 1 (via Alpha, AS path 65002 65001, MED 100, Local Preference 200)

Question 22

A network architect for a global ISP is tasked with ensuring optimal traffic flow to a newly established, high-capacity data center facility. This facility is connected via multiple upstream providers and direct peering arrangements. The architect needs to implement a BGP routing policy that prioritizes connectivity through a specific upstream provider, known for its low-latency backbone and favorable peering with the data center\'s hosting entity. The policy must also consider potential future expansions and maintain flexibility in adapting to changes in network topology or provider agreements. Which combination of BGP attribute manipulation and policy implementation best achieves this objective, demonstrating a nuanced understanding of BGP\'s decision-making process and strategic network design?

Accepted Answer

Setting a high LOCAL_PREF on routes learned from the preferred upstream provider, advertising a lower MED to the data center's peering partner, and utilizing custom communities to tag these optimal paths for internal traffic engineering.

Question 23

A multinational ISP, \"GlobalConnect\" (AS 65000), is experiencing intermittent route instability and suboptimal traffic flow on its primary transit link connecting to AS 65001. This instability appears to be related to differing path selection preferences between GlobalConnect and AS 65001, as well as suboptimal inbound routing from AS 65002, another major transit provider. GlobalConnect wishes to engineer traffic such that inbound traffic from AS 65001 preferentially utilizes a path through AS 65002 (which offers lower latency), and inbound traffic from AS 65002 to GlobalConnect\'s network prefers a direct peering rather than a transit path through AS 65001. Given these objectives, what BGP attribute manipulation strategy should GlobalConnect implement on its peering sessions with AS 65001 and AS 65002 to achieve stable and preferred traffic flow?

Accepted Answer

On the BGP session with AS 65001, set a lower MED for routes advertised to AS 65001 to encourage their outbound path through AS 65002. On the BGP session with AS 65002, set a higher LOCAL_PREF for routes learned directly from AS 65002 to favor direct inbound traffic.

Question 24

Consider a network administrator in AS65001 implementing a policy to attract inbound traffic from external ASes. They configure BGP to advertise a higher Local Preference value (200) for routes learned from AS65002, while routes learned from AS65003 are advertised with a lower Local Preference value (100). Both AS65002 and AS65003 are peers with AS65001 and advertise the same destination prefix. Given that AS65002 has multiple paths to reach the destination prefix, and one of these paths involves traversing fewer AS hops than the paths available to AS65003, how will AS65002 likely select its path to send traffic towards the destination prefix via AS65001, considering the administered Local Preference values?

Accepted Answer

AS65002 will select the path to AS65001 that has the shortest AS_PATH, irrespective of the Local Preference value AS65001 assigned to the inbound route.

Question 25

A network administrator for \"Aether Dynamics,\" a global logistics firm, is managing BGP peering with a key transit provider. The transit provider, in an effort to optimize their internal routing for a newly acquired subnet, announces a more specific route (e.g., /23) for a range of IP addresses that was previously covered by a broader prefix (e.g., /22) announced by the same provider. This change, while intended to improve efficiency on the provider\'s side, causes intermittent packet loss and reachability issues for Aether Dynamics\' European branch offices that rely on this specific IP range. The administrator must quickly stabilize the network. Which of the following actions would best demonstrate adaptability and effective problem-solving in this BGP scenario, aligning with best practices for network stability and operational continuity?

Accepted Answer

Modify the inbound BGP policy on Aether Dynamics' edge routers to accept the new, more specific prefix announcement from the transit provider, ensuring the longest-prefix match rule is correctly handled.

Question 26

A network administrator is configuring BGP on an Alcatel-Lucent router and observes multiple learned paths to a specific destination prefix. To ensure optimal traffic flow within their Autonomous System, the administrator wants to influence the router\'s decision-making process. Considering the standard BGP path selection algorithm as implemented in Alcatel-Lucent environments, which of the following attributes, when configured with a higher value, would typically lead to the selection of a particular path over others with otherwise equal BGP attributes?

Accepted Answer

Local Preference

Question 27

A critical BGP peering session between AS 65001 (managed by your organization) and AS 65002, carrying essential transit traffic, has unexpectedly dropped. Initial diagnostics indicate that the session failed to reach the \'Established\' state after AS 65002 implemented a significant modification to their inbound routing policy, involving extensive AS-PATH prepending and the introduction of new BGP communities. Your team has confirmed that the peering IP addresses and AS numbers remain unchanged, and no authentication issues are present. What is the most crucial initial step to diagnose and resolve this BGP session failure?

Accepted Answer

Thoroughly review and validate the BGP configuration on your local router, specifically focusing on the inbound policy statements and negotiated capabilities that might be incompatible with AS 65002's newly implemented, restrictive inbound routing policy.

Question 28

An Alcatel-Lucent router, configured as an ASBR with AS number 200, establishes a BGP peering session with an external AS, 65001. A route-map, applied inbound on this session, contains a `set as-path prepend 200 200` statement. Considering this configuration, what is the most accurate description of the immediate and direct impact on the router\'s BGP table entries and its own outbound route advertisements to its internal BGP peers?

Accepted Answer

The AS_PATH attribute of routes learned from the external peer will be prepended with '200 200' in the router's BGP table, but its own locally originated route advertisements to internal peers will not have their AS_PATH modified by this specific inbound policy.

Question 29

Consider a network administrator configuring BGP on an Alcatel-Lucent (Nokia) router. The router has learned two distinct paths to the same destination prefix from different neighbors. Path Alpha is advertised with a local preference of 100 and an AS_PATH attribute indicating traversal through two external Autonomous Systems. Path Beta is advertised with a local preference of 150 and an AS_PATH attribute indicating traversal through three external Autonomous Systems. Which path will the router select as the optimal route, and why does this selection occur based on standard BGP path selection criteria?

Accepted Answer

Path Beta will be selected because a higher local preference value is prioritized over a shorter AS_PATH length in the BGP best path selection process.

Question 30

Considering a network administrator for \"AuraConnect Telecoms\" managing a critical transit AS, the Border Gateway Protocol router has received three distinct paths to the 192.168.1.0/24 prefix from different upstream providers. Path A is advertised with a local preference of 120 and an AS-PATH length of 3. Path B is advertised with a local preference of 100 and an AS-PATH length of 2. Path C is advertised with a local preference of 120, an AS-PATH length of 3, and a Multi-Exit Discriminator (MED) of 50. Assuming all other BGP attributes are either identical or not relevant for selection at this stage, which path will the router ultimately select as the best path for the 192.168.1.0/24 prefix?

Accepted Answer

Path C

4A0102 AlcatelLucent Border Gateway Protocol Free Practice Test — 30 Questions

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