Knowledge + Practice

CCNA Architecture Questions

75 of 232 questions · Page 1/4 · Architecture · Answers revealed

Practice these questions Domain overview All questions

1

MCQhard

A service provider is deploying Segment Routing (SR) with TI-LFA for fast convergence. Which mechanism does TI-LFA use to repair a link failure in a node segment path?

A.Precomputes a backup path using a segment list (label stack) that avoids the failed link

B.Uses loop-free alternate (LFA) as defined in IPFRR

C.Uses RSVP-TE to signal a protected LSP

D.Relies on BFD to trigger a backup path in the forwarding table

AnswerA

TI-LFA precomputes a backup path by inserting a segment list to steer traffic around the failure.

Why this answer

TI-LFA (Topology Independent Loop-Free Alternate) precomputes a backup path using a segment list (label stack) that explicitly avoids the failed link. This is achieved by encoding a repair path as a sequence of adjacency and node segments, ensuring that traffic is steered around the failure without loops, regardless of the network topology. The backup path is installed in the forwarding table before the failure occurs, enabling sub-50ms convergence.

Exam trap

Cisco often tests the misconception that TI-LFA is just an extension of classic LFA (Option B), but the key differentiator is that TI-LFA is topology-independent and uses a segment list, not a simple LFA next-hop.

How to eliminate wrong answers

Option B is wrong because TI-LFA is topology-independent and does not rely on the loop-free alternate (LFA) condition defined in IPFRR (RFC 6571), which fails in many topologies (e.g., ring or square). Option C is wrong because TI-LFA is a Segment Routing mechanism and does not use RSVP-TE to signal a protected LSP; RSVP-TE is a separate MPLS-TE technology. Option D is wrong because BFD is used for fast failure detection, not for computing or installing the backup path; TI-LFA precomputes the backup path independently of BFD.

Practice this question →

2

MCQhard

A service provider is implementing MPLS-TE with FRR (Fast Reroute) using one-to-one backup tunnels. After activation, they notice that the number of labels in the forwarding table has increased significantly. What is the most likely reason for this increase?

A.One-to-one backup creates a unique backup tunnel for each protected LSP

B.RSVP-TE signaling is not properly aggregating labels

C.Penultimate Hop Popping (PHP) is disabled

D.Facility backup is being used instead of one-to-one

AnswerA

Each protected LSP gets its own backup tunnel, increasing label count linearly.

Why this answer

One-to-one backup tunnels in MPLS-TE FRR create a dedicated backup LSP for each protected primary LSP. This means every primary LSP gets its own unique set of labels for the backup path, leading to a significant increase in the number of labels in the forwarding table. In contrast, facility backup shares a single bypass tunnel among multiple protected LSPs, which conserves labels.

Exam trap

Cisco often tests the distinction between one-to-one and facility backup, where candidates may confuse the label increase with a signaling or PHP issue, rather than recognizing it as a direct consequence of the one-to-one backup design.

How to eliminate wrong answers

Option B is wrong because RSVP-TE signaling does aggregate labels for the primary LSP, but the label increase is a direct consequence of the one-to-one backup design, not a signaling failure. Option C is wrong because disabling PHP would affect label imposition at the penultimate hop, but it does not cause a significant increase in the number of labels; PHP affects label stack depth, not the count of unique backup labels. Option D is wrong because facility backup (bypass tunnels) actually reduces label usage by sharing a single backup tunnel among multiple LSPs, which is the opposite of the observed increase.

Practice this question →

3

MCQmedium

Refer to the exhibit. A PE router is showing a VRF route. What does the [200/0] indicate?

A.Administrative distance 200 and metric 0

B.Local preference 200 and MED 0

C.Label value 200 and metric 0

D.AS path length 200 and weight 0

AnswerA

BGP external routes have AD 200.

Why this answer

In the VRF route output, the [200/0] notation represents the administrative distance (200) and the metric (0) for the route. The administrative distance is a trustworthiness value used by the router to select the best path when multiple routing protocols provide routes to the same destination; a lower value is preferred. The metric is a protocol-specific cost, and here it is 0, indicating a directly connected or very low-cost path within the VRF.

Exam trap

Cisco often tests the distinction between BGP path attributes (like local preference, MED, AS path, weight) and the standard IP routing table fields (administrative distance and metric), causing candidates to confuse the [AD/metric] format with BGP-specific values.

How to eliminate wrong answers

Option B is wrong because local preference and MED are BGP path attributes, not represented in the [AD/metric] format; local preference is shown as 'localpref' in BGP table output, and MED is shown separately. Option C is wrong because label values are MPLS-related and appear in the 'Labels' field of a VRF or MPLS forwarding table, not in the [200/0] format which is standard for administrative distance and metric. Option D is wrong because AS path length is a BGP attribute shown in the 'AS path' column, and weight is a Cisco-specific BGP attribute displayed in the 'weight' column; neither is represented as [value/value] in a VRF route entry.

Practice this question →

4

MCQeasy

A service provider wants to offer Layer 2 VPN services using MPLS. Which technology should be used to transport Ethernet frames across the MPLS core?

A.Pseudowire

B.LDP

C.VPLS

D.L3VPN

AnswerA

Pseudowire provides point-to-point Layer 2 transport over MPLS.

Why this answer

Pseudowire (A) is the correct technology because it provides a point-to-point Layer 2 circuit over an MPLS core, allowing Ethernet frames to be encapsulated and transported transparently. This is defined in RFC 4448 (Ethernet over MPLS) and enables service providers to offer E-Line services. Pseudowire uses MPLS labels to forward frames across the core without requiring the core routers to participate in the customer's Layer 2 control plane.

Exam trap

Cisco often tests the distinction between point-to-point (Pseudowire) and multipoint (VPLS) Layer 2 services, so the trap here is that candidates may confuse VPLS as the answer because it also transports Ethernet frames, but the question specifies 'Layer 2 VPN services' without mentioning multipoint, making Pseudowire the correct choice.

How to eliminate wrong answers

Option B (LDP) is wrong because LDP is a label distribution protocol used to distribute MPLS labels for building LSPs, not a technology for transporting Ethernet frames. Option C (VPLS) is wrong because VPLS provides multipoint-to-multipoint Layer 2 connectivity (E-LAN), not the point-to-point Ethernet transport described in the question. Option D (L3VPN) is wrong because L3VPN operates at Layer 3, routing IP packets based on customer VPN routes, and does not transport raw Ethernet frames across the MPLS core.

Practice this question →

5

MCQhard

A service provider is deploying multicast over MPLS L3VPN. Which mechanism is used to provide multicast in the core between PE routers?

A.IGMP

B.PIM-SM

C.PIM-DM

D.mLDP

AnswerD

mLDP is the multicast label distribution protocol for MPLS.

Why this answer

In an MPLS L3VPN multicast deployment, the core network between PE routers uses a label-based multicast mechanism rather than a traditional PIM protocol. mLDP (Multipoint LDP) is the correct choice because it establishes point-to-multipoint (P2MP) LSPs in the MPLS core, enabling efficient multicast transport without requiring PIM in the core. This approach is defined in RFC 6388 and is commonly used for MVPN (Multicast VPN) implementations.

Exam trap

Cisco often tests the misconception that PIM-SM is always required for multicast in any network, but in an MPLS L3VPN core, the correct mechanism is mLDP or RSVP-TE P2MP, as PIM is typically confined to the customer edge or the PE-CE link.

How to eliminate wrong answers

Option A is wrong because IGMP is a host-to-router protocol used for managing multicast group memberships on the last hop, not for multicast routing in the MPLS core between PEs. Option B is wrong because PIM-SM (Protocol Independent Multicast - Sparse Mode) is a multicast routing protocol that could be used in the core, but in an MPLS L3VPN context, the core typically uses label-based multicast (mLDP or RSVP-TE P2MP) to avoid running PIM across the provider backbone, as per the MVPN architecture. Option C is wrong because PIM-DM (Dense Mode) is a flood-and-prune multicast protocol that is inefficient for a service provider core and is not the standard mechanism for multicast transport over MPLS L3VPNs.

Practice this question →

6

MCQmedium

A service provider is redesigning its MPLS core to support both L3VPN and L2VPN services. They want to minimize the number of labels in the forwarding table while maintaining per-VRF label allocation. Which label allocation mode should be used for the L3VPN service?

A.Per-VRF label allocation

B.Per-CE label allocation

C.Per-prefix label allocation

D.Per-instance label allocation

AnswerA

Per-VRF assigns a single label per VRF, minimizing labels while allowing per-VRF forwarding.

Why this answer

Per-VRF label allocation assigns a single MPLS label per VRF, meaning all routes within a VRF share the same label. This minimizes the number of labels in the forwarding table compared to per-prefix allocation, while still maintaining per-VRF isolation for L3VPN services. It is the recommended mode when the goal is to reduce label consumption without sacrificing VPN separation.

Exam trap

Cisco often tests the distinction between per-VRF and per-prefix label allocation, where candidates mistakenly choose per-prefix because they think it offers finer granularity, but the question explicitly asks for minimizing labels, which per-VRF achieves.

How to eliminate wrong answers

Option B (Per-CE label allocation) is wrong because it assigns a label per customer edge (CE) router, which does not directly minimize labels in the core and is not a standard L3VPN label mode; it is more relevant to Carrier Supporting Carrier (CSC) or inter-AS scenarios. Option C (Per-prefix label allocation) is wrong because it assigns a unique label for each prefix in the VRF, which maximizes label usage and contradicts the goal of minimizing labels in the forwarding table. Option D (Per-instance label allocation) is wrong because it is not a recognized label allocation mode in MPLS L3VPN; the correct terms are per-VRF, per-prefix, or per-CE, and 'per-instance' is a distractor.

Practice this question →

7

Multi-Selectmedium

Which TWO statements accurately describe the differences between GPON and XGS-PON? (Choose two.)

Select 2 answers

A.XGS-PON uses passive optical splitters.

B.GPON offers higher downstream bandwidth than XGS-PON.

C.GPON requires active amplification in the field.

D.XGS-PON supports symmetric 10 Gbps speeds.

E.GPON uses WDM while XGS-PON does not.

AnswersA, D

Both GPON and XGS-PON are passive optical networks.

Why this answer

XGS-PON provides symmetric 10 Gbps, while GPON is asymmetric (2.5G/1.25G). Both use passive optical splitters and WDM.

Practice this question →

8

MCQmedium

Which MEF service type provides a point-to-point Ethernet connection between two user-network interfaces (UNIs)?

A.E-Line

B.E-LAN

C.E-Tree

D.E-Access

AnswerA

E-Line is point-to-point.

Why this answer

E-Line is the MEF service for point-to-point Ethernet connectivity.

Practice this question →

9

MCQmedium

Which technology provides Layer 2 multipoint connectivity over an MPLS network, where customer sites appear to be on the same Ethernet broadcast domain?

A.L3VPN

B.VPWS (Virtual Private Wire Service)

C.EVPN

D.VPLS

AnswerD

VPLS creates a multipoint Ethernet broadcast domain over MPLS.

Why this answer

VPLS (Virtual Private LAN Service) emulates a multipoint Ethernet LAN over MPLS. VPWS is point-to-point, EVPN is modern but not always broadcast, and L3VPN is layer 3.

Practice this question →

10

MCQhard

A service provider is deploying an MPLS L3VPN solution for a customer with two sites. The PE routers are running OSPF as the IGP and LDP for label distribution. The provider wants to ensure that customer traffic is load-balanced across two equal-cost paths between the PEs. The network team notices that all traffic is taking only one path despite the IGP showing equal-cost routes. The team has verified that the MPLS forwarding table on the P router shows only one label entry for the BGP next-hop. The team suspects a load-balancing issue. Which action best resolves the problem?

A.Increase the OSPF maximum-paths value to 4

B.Enable per-flow load balancing on all routers with 'load-balance per-flow'

C.Enable BGP additional-paths on the PE routers

D.Configure LDP to use the 'mpls ldp igp sync' command

AnswerB

This enables load balancing based on flow, which is required for MPLS to use multiple equal-cost paths.

Why this answer

The issue is that MPLS L3VPN traffic is not being load-balanced despite equal-cost IGP paths. This typically occurs when the MPLS forwarding table on the P router has only one label entry for the BGP next-hop, indicating that per-flow load balancing is not enabled. Enabling 'load-balance per-flow' on all routers ensures that the CEF (Cisco Express Forwarding) uses per-flow hashing to distribute traffic across multiple equal-cost LSPs (Label Switched Paths), rather than per-packet or default behavior that may favor a single path.

Exam trap

Cisco often tests the misconception that IGP equal-cost routes automatically guarantee MPLS load balancing, but the trap here is that MPLS forwarding uses the label entry for the BGP next-hop, and without per-flow load balancing, the router may install only one label entry in the LFIB (Label Forwarding Information Base) for that next-hop, causing all traffic to follow a single path.

How to eliminate wrong answers

Option A is wrong because increasing OSPF maximum-paths to 4 does not address the MPLS label-level load-balancing issue; the IGP already shows equal-cost routes, so the problem lies in how MPLS forwards traffic across those paths, not in route selection. Option C is wrong because BGP additional-paths is used to advertise multiple paths for a prefix to avoid path-hiding in BGP, but it does not affect how the MPLS forwarding table load-balances traffic across existing equal-cost LSPs; the issue is on the P router, not BGP path advertisement. Option D is wrong because 'mpls ldp igp sync' ensures LDP and IGP are synchronized to prevent blackholing during convergence, but it does not enable load balancing across multiple LSPs; the problem is not synchronization but the lack of per-flow hashing in the forwarding plane.

Practice this question →

11

MCQmedium

An SP is deploying MPLS in the core/backbone to support L3VPN services. What is the purpose of MP-BGP in an MPLS VPN architecture?

A.To exchange customer VPN routes and VPN labels between PE routers

B.To forward data packets across the MPLS core

C.To establish IGP adjacencies between PE and CE routers

D.To distribute MPLS labels for LSPs

AnswerA

MP-BGP carries VPNv4 routes with route distinguishers and VPN labels.

Why this answer

MP-BGP (Multiprotocol BGP) carries VPNv4 routes between PE routers, including the VPN label, enabling customer isolation and reachability across the MPLS core.

Practice this question →

12

MCQmedium

A provider is implementing EVPN for data center interconnect. They require multi-homing with all-active load balancing and fast convergence using BGP. Which EVPN feature enables this?

A.MPLS Traffic Engineering

B.Ethernet Segment Identifier (ESI)

C.BGP Link-State

D.VPLS with BGP autodiscovery

AnswerB

Correct. ESI identifies the multi-homed segment and enables all-active load balancing.

Why this answer

EVPN uses Ethernet Segment Identifier (ESI) for multi-homing. All-active mode allows load balancing across multiple PE nodes, and BGP control plane provides fast convergence via route withdrawal.

Practice this question →

13

MCQhard

An SP deploys EVPN to provide L2VPN services with multi-homing. The customer CE is dual-homed to two different PE routers. Which EVPN mechanism ensures that only one PE forwards traffic to the CE for a given Ethernet segment, preventing loops?

A.BGP Route Reflector

B.MAC learning via data plane

C.Split horizon groups

D.Designated Forwarder election based on ESI

AnswerD

DF election ensures only one PE forwards BUM traffic to the CE.

Why this answer

Ethernet Segment Identifier (ESI) and designated forwarder (DF) election in EVPN ensure that only one PE forwards traffic to the CE for a given Ethernet segment, preventing loops.

Practice this question →

14

MCQhard

A large SP network uses Segment Routing (SR) with MPLS data plane. They want to enforce a strict path for certain traffic flows across the core while using shortest-path for others. Which technique should be used?

A.SR-TE with explicit path using segment list

B.Using TI-LFA

C.Configuring bandwidth reservation on all links

D.Using SR policies with color extended community based on BGP

AnswerA

SR-TE with a segment list defines the exact path through the network.

Why this answer

SR-TE with an explicit path using a segment list allows the operator to define a strict, ordered list of MPLS labels (segments) that the traffic must follow, overriding the default IGP shortest-path behavior. This is the correct technique for enforcing a strict path across the core while leaving other traffic to use shortest-path forwarding.

Exam trap

Cisco often tests the distinction between SR-TE explicit paths (which enforce strict hop-by-hop routing) and SR policies using color communities (which are more about traffic steering based on BGP attributes, not strict path enforcement).

How to eliminate wrong answers

Option B is wrong because TI-LFA (Topology Independent Loop-Free Alternate) is a fast-reroute mechanism that provides local protection against link or node failures, not a method for enforcing strict traffic paths. Option C is wrong because bandwidth reservation on all links is a capacity-planning or RSVP-TE feature, not a Segment Routing technique, and it does not enforce a strict path for specific flows. Option D is wrong because SR policies with color extended community based on BGP are used for steering traffic into SR-TE tunnels based on BGP attributes, but the question specifically asks for a strict path enforcement, which is achieved by an explicit segment list, not just a color-based policy.

Practice this question →

15

Multi-Selecteasy

Which two protocols are commonly used for label exchange in an MPLS network? (Choose two.)

Select 2 answers

A.OSPF

B.PIM

C.LDP

D.BGP

E.IS-IS

AnswersC, D

LDP exchanges labels for IGP prefixes.

Why this answer

LDP (Label Distribution Protocol) is a standardized protocol (RFC 5036) specifically designed for distributing MPLS labels between routers to establish Label Switched Paths (LSPs) without requiring an IGP to carry label information. BGP (Border Gateway Protocol) can also exchange MPLS labels, particularly in MPLS VPN and Inter-AS scenarios, where it carries VPNv4 routes with MPLS labels using the BGP label-mapping capability (RFC 3107).

Exam trap

Cisco often tests the misconception that IGPs like OSPF or IS-IS can be used for MPLS label exchange because they are commonly associated with MPLS traffic engineering extensions, but those extensions (e.g., OSPF-TE) only carry link attributes, not labels.

Practice this question →

16

MCQmedium

A service provider is troubleshooting a BGP route advertisement issue. Routes from a customer are not being advertised to the upstream provider. The PE router is configured with 'neighbor 10.0.0.1 route-map RMAP out'. The route-map RMAP permits the customer prefix. However, the BGP table on the PE shows the prefix as valid but not advertised. What is a likely cause?

A.The next-hop is not reachable from the upstream provider

B.The BGP session to the upstream provider is flapping

C.The prefix is not in the global routing table

D.The route-map is applied inbound instead of outbound

AnswerA

If next-hop-self is not used, the next-hop might be a customer-facing interface not reachable upstream.

Why this answer

The BGP table shows the prefix as valid but not advertised, which indicates that BGP has the route but is not sending it to the upstream neighbor. A common cause is that the next-hop for the customer prefix is not reachable from the PE router via the interface used to reach the upstream provider. BGP will not advertise a route if the next-hop is not reachable in the routing table (unless 'neighbor x.x.x.x next-hop-self' is configured), because the upstream router would be unable to forward traffic to that next-hop.

Exam trap

Cisco often tests the subtle distinction between a prefix being 'valid' (next-hop reachable in the global routing table) and 'advertised' (next-hop reachable from the specific neighbor's perspective), leading candidates to overlook next-hop reachability as the root cause.

How to eliminate wrong answers

Option B is wrong because a flapping BGP session would cause the session to go up and down, resulting in prefixes being withdrawn and re-advertised, not a stable 'valid but not advertised' state. Option C is wrong because if the prefix were not in the global routing table, it would not appear as valid in the BGP table; BGP requires the prefix to be in the routing table (or have a valid route) to be considered valid. Option D is wrong because the question states the route-map is applied outbound, and if it were mistakenly applied inbound, the prefix would still be advertised (the outbound filter would not exist), and the issue would be with receiving routes, not advertising them.

Practice this question →

17

Multi-Selecthard

A service provider is implementing Segment Routing (SR) with MPLS. Which three statements are true regarding SR-MPLS? (Choose three.)

Select 3 answers

A.SR-MPLS supports traffic engineering only with a central controller

B.SR-MPLS does not require LDP or RSVP-TE

C.The SRGB must be globally unique across the domain

D.Adjacency SIDs are advertised via BGP-LS

E.Prefix-SIDs are bound to node loopbacks

AnswersB, C, E

SR uses IGP to distribute labels, eliminating the need for LDP or RSVP-TE.

Why this answer

B is correct because SR-MPLS uses the MPLS data plane but replaces the control plane protocols LDP and RSVP-TE with IGP extensions (IS-IS or OSPF) to distribute segment information. This eliminates the need for these traditional label distribution protocols, simplifying network operations and reducing protocol overhead.

Exam trap

Cisco often tests the misconception that SR-MPLS requires a central controller for traffic engineering, but in reality, it supports both centralized and distributed TE models, and the key differentiator is the elimination of LDP/RSVP-TE.

Practice this question →

18

MCQmedium

A service provider is deploying EVPN-VPWS for point-to-point services. They have set up an EVPN instance with Ethernet Segment Identifier (ESI) and EVI. After configuration, the pseudowire is not coming up. Which misconfiguration is most likely?

A.The same EVI is used on both PEs.

B.The ESI is all-zeros.

C.The MTU mismatch on the attachment circuits.

D.The BGP EVPN address-family is not activated.

AnswerD

Correct. The BGP EVPN address-family must be activated on both PEs to exchange EVPN routes. Without it, the PEs cannot advertise or receive the necessary per-EVI AD routes, and the pseudowire will not be established.

Why this answer

In EVPN-VPWS, the EVI (EVPN Instance) must be the same on both PEs for the same point-to-point service to ensure proper route matching and label assignment. Therefore, using the same EVI is correct and not a misconfiguration. The most likely issue is that the BGP EVPN address-family is not activated on the PEs.

Without this address-family, the PEs cannot exchange EVPN routes (e.g., Type 1 per-EVI AD routes), so the pseudowire cannot be established. The other options—ESI all-zeros (acceptable for single-homed) and MTU mismatch (would cause operational issues but not prevent pseudowire from coming up at the control-plane level)—are less likely to be the root cause.

Exam trap

Candidates may mistakenly think that the EVI must be unique per PE, but in EVPN-VPWS the EVI must match across PEs for the same service. The real misconfiguration is often forgetting to activate the BGP EVPN address-family.

How to eliminate wrong answers

Option B is wrong because an ESI of all-zeros is a valid configuration for single-homed endpoints in EVPN-VPWS; it does not prevent the pseudowire from coming up. Option C is wrong because an MTU mismatch on the attachment circuits would cause operational issues or packet drops, but it would not prevent the pseudowire control plane from establishing; the pseudowire can still come up with an MTU mismatch. Option D is wrong because if the BGP EVPN address-family is not activated, the PE would not exchange EVPN routes at all, and the pseudowire would not be advertised; however, the question states the pseudowire is not coming up after configuration, implying BGP EVPN is likely activated but the EVI misconfiguration is the specific cause.

Practice this question →

19

MCQmedium

A service provider has deployed QoS on its MPLS backbone to offer different classes of service. The provider notices that EF (Expedited Forwarding) traffic sometimes experiences high jitter during congestion. Following recommended practices, which action is MOST likely to reduce jitter for EF traffic?

A.Use priority queuing (LLQ) for EF traffic with a policer

B.Apply traffic shaping on all EF packets at the edge

C.Change the DSCP value of EF traffic to AF41 to reduce drops

D.Apply weighted random early detection (WRED) on the EF queue

AnswerA

LLQ gives strict priority, minimizing jitter by servicing EF first.

Why this answer

Priority queuing (LLQ) with a policer ensures EF traffic is served strictly before other queues, reducing jitter, while the policer prevents EF traffic from monopolizing bandwidth. Option B is wrong because traffic shaping smooths bursts but does not provide priority treatment during congestion, so jitter can still occur. Option C is wrong because changing DSCP to AF41 would reclassify EF traffic to a lower priority class, potentially increasing jitter and delay.

Option D is wrong because WRED is a congestion avoidance mechanism that drops packets randomly, which can cause jitter for EF traffic; EF should be exempt from WRED.

Practice this question →

20

MCQmedium

Which statement about the commit/rollback configuration model in IOS XR is true?

A.Rollback requires manual deletion of uncommitted changes

B.Configuration is applied to all cards simultaneously without validation

C.If a commit fails, the system automatically rolls back to the last committed configuration

D.Changes take effect immediately without a commit command

AnswerC

The commit model ensures atomicity: on failure, changes are discarded.

Why this answer

IOS XR uses a two-phase commit: the user commits, and if successful, the configuration is applied; otherwise, it rolls back. There is no need for explicit rollback commands.

Practice this question →

21

MCQhard

An ISP is deploying EVPN-VXLAN for its data center interconnect. Which statement about control-plane learning is correct?

A.MAC addresses are learned via IRB

B.MAC addresses are learned via OSPF

C.MAC addresses are learned via BGP MP-BGP EVPN address family

D.MAC addresses are learned via VXLAN data plane

AnswerC

EVPN uses BGP for MAC route advertisement.

Why this answer

In EVPN-VXLAN deployments for data center interconnect, MAC address learning occurs via the control plane using BGP with the MP-BGP EVPN address family (AFI 25 / SAFI 70). This eliminates the need for traditional data-plane flooding and learning, providing better scalability and control. The correct statement is that MAC addresses are learned via BGP MP-BGP EVPN address family.

Exam trap

Cisco often tests the distinction between control-plane learning (EVPN via BGP) and data-plane learning (traditional VXLAN flood-and-learn), and candidates mistakenly associate VXLAN with data-plane learning even when EVPN is specified.

How to eliminate wrong answers

Option A is wrong because IRB (Integrated Routing and Bridging) is a function that provides Layer 3 gateway services for VXLAN segments, not a mechanism for MAC address learning. Option B is wrong because OSPF is a link-state routing protocol used for IP routing, not for MAC address learning in EVPN environments. Option D is wrong because VXLAN data-plane learning (flood-and-learn) is a legacy approach that EVPN explicitly replaces with control-plane learning to avoid flooding and improve convergence.

Practice this question →

22

MCQhard

You are a network architect for a large service provider. The network consists of multiple core routers (P routers) and edge routers (PE routers) supporting both L3VPN and L2VPN services. The network currently uses LDP for label distribution and has a flat IGP (OSPF) design. Recently, there have been scalability issues: the IGP convergence time has increased significantly, and the OSPF link-state database (LSDB) has grown large, causing high CPU utilization on core routers. Additionally, the LDP sessions are taking longer to establish after a router reboot. You are tasked with redesigning the network to improve scalability and convergence. The budget allows for significant changes but cannot replace all hardware. Which approach best addresses the scalability issues while minimizing disruption?

A.Upgrade OSPF to OSPFv3 to support IPv6 and improve performance

B.Implement Segment Routing (SR-MPLS) to replace LDP and reduce IGP overhead

C.Introduce IS-IS as a second IGP to offload traffic from OSPF, and use route redistribution between the two protocols

D.Replace OSPF with BGP as the core IGP to reduce link-state overhead

AnswerB

SR-MPLS eliminates LDP and reduces IGP LSDB size because SIDs are advertised as TLV extensions, reducing the number of LSA types.

Why this answer

Segment Routing (SR-MPLS) eliminates the need for LDP by encoding MPLS labels directly in the IGP (OSPF or IS-IS) using extensions, which reduces control-plane overhead and speeds up convergence. This directly addresses the large OSPF LSDB and slow LDP session establishment because SR-MPLS does not require a separate label distribution protocol and can leverage a single IGP for both routing and label information, improving scalability without hardware replacement.

Exam trap

Cisco often tests the misconception that adding a second IGP or upgrading to OSPFv3 will improve scalability, when in fact the real issue is the overhead of a separate label distribution protocol (LDP) and the LSDB size, which Segment Routing directly addresses by integrating label distribution into the IGP.

How to eliminate wrong answers

Option A is wrong because OSPFv3 is an IPv6 routing protocol that does not inherently reduce LSDB size or improve convergence; it would add IPv6 overhead without solving the core LDP and IGP scalability issues. Option C is wrong because introducing IS-IS as a second IGP with route redistribution would increase complexity, LSDB size, and convergence time due to mutual redistribution loops and administrative overhead, making scalability worse. Option D is wrong because BGP is not designed as an IGP; it lacks fast convergence and link-state awareness, and using it as a core IGP would introduce path-vector convergence delays and require full-mesh or route reflectors, increasing rather than reducing overhead.

Practice this question →

23

MCQmedium

Refer to the exhibit. The router is configured as a PE router in an MPLS VPN network. Which option correctly identifies a configuration error that would prevent proper operation?

A.The neighbor remote-as should be the same AS number for iBGP

B.The interface lacks the 'mpls ip' command

C.The OSPF network statement uses an incorrect wildcard mask

D.The BGP network statement does not match the interface prefix

AnswerC

The wildcard mask 0.255.255.255 is too broad and does not match the /30 prefix correctly.

Why this answer

The OSPF network statement uses a wildcard mask of 0.0.0.0, which matches only the exact IP address 10.1.1.1, but the interface has a /30 prefix (255.255.255.252), so the correct wildcard mask should be 0.0.0.3 to include the entire subnet. This misconfiguration prevents OSPF from advertising the correct network, breaking MPLS VPN CE-to-PE routing.

Exam trap

Cisco often tests the distinction between OSPF wildcard masks and subnet masks, where candidates mistakenly think any wildcard mask that includes the interface IP is sufficient, but the mask must match the subnet exactly for OSPF to advertise the correct network.

How to eliminate wrong answers

Option A is wrong because the neighbor remote-as for iBGP should be the same AS number as the router's own BGP AS, and the exhibit shows neighbor 10.1.1.2 remote-as 65000, which matches the router's BGP AS 65000, so this is correct. Option B is wrong because the interface configuration includes 'mpls ip' under interface GigabitEthernet0/0, so MPLS is enabled on that interface. Option D is wrong because the BGP network statement uses 'network 10.1.1.0 mask 255.255.255.252', which exactly matches the /30 prefix on the interface, so it is correctly configured.

Practice this question →

24

Multi-Selectmedium

A service provider is designing an MPLS L3VPN network to provide Layer 3 VPN services to multiple customers. Which two statements correctly describe the roles of the Provider Edge (PE) and Customer Edge (CE) routers in this architecture?

Select 2 answers

A.P routers store all customer VPN routes in their global routing table.

B.CE routers perform MPLS label switching between PE routers.

C.PE routers advertise customer routes via MP-BGP with route distinguishers and route targets.

D.CE routers participate in the service provider's IGP to exchange loopback addresses.

E.PE routers maintain separate VRF tables for each customer VPN.

AnswersC, E

Correct. MP-BGP is used to distribute VPNv4 routes with RD and RT.

Why this answer

In an MPLS L3VPN, PE routers use MP-BGP (Multiprotocol BGP) to exchange customer VPN routes. Each VPN route is uniquely identified by a Route Distinguisher (RD) to maintain global uniqueness, and Route Targets (RTs) control the import/export of routes between VRFs. This allows the PE to separate customer routing domains while still using a shared MPLS backbone.

Exam trap

The trap here is that candidates often confuse the roles of P and PE routers, mistakenly thinking P routers store customer routes or that CE routers participate in MPLS label switching, when in fact P routers are label-switching only and CE routers are MPLS-unaware.

Practice this question →

25

MCQeasy

Which access technology is based on ITU-T G.984 and provides downstream speeds up to 2.488 Gbps?

A.GPON

B.XGS-PON

C.DSL

D.EPON

AnswerA

GPON provides 2.488 Gbps downstream.

Why this answer

GPON (Gigabit-PON) is defined by ITU-T G.984 with downstream up to 2.488 Gbps.

Practice this question →

26

MCQeasy

An SP is deploying a Quality of Service (QoS) architecture in its core network to support multiple services: voice, video, and data. The core routers use MPLS and implement QoS based on the MPLS EXP bits. The architecture must ensure that voice packets are never dropped, even during congestion, while allowing video to have higher priority than data. The current design marks voice with EXP 4, video with EXP 3, and data with EXP 0. During a traffic burst, voice traffic is being dropped, which should not happen. The core routers have the following queue configuration: (1) a priority queue (PQ) for EXP 4+5, (2) a bandwidth queue for EXP 2-3, (3) a default queue for EXP 0-1. What is most likely the cause of voice drops?

A.Voice traffic is being marked with EXP 4 but the priority queue also includes EXP 5, which may cause policing.

B.The bandwidth queue for video is configured to borrow from the priority queue.

C.The priority queue is not strictly priority; it shares bandwidth with other queues.

D.The priority queue is rate-limited by a policer that shapes traffic to a certain bandwidth.

AnswerD

Correct. Many implementations use a policer on the priority queue to prevent starvation; if the police rate is too low, voice packets are dropped.

Why this answer

Voice drops occur because the priority queue is often rate-limited by a policer to prevent starvation of other queues. If the policer rate is set too low, voice packets are dropped during bursts. Strict priority without policing does not drop, but policing is common in SP core to protect other queues.

The bandwidth queue and default queue are not the issue.

Practice this question →

27

Multi-Selecthard

Which THREE are requirements for deploying MPLS Traffic Engineering with RSVP-TE?

Select 3 answers

A.OSPFv3 must be the IGP

B.LDP must be enabled on all routers

C.Links must have reservable bandwidth advertised

D.CSPF (Constrained SPF) must be implemented for path calculation

E.RSVP-TE signaling protocol must be configured

AnswersC, D, E

Bandwidth reservations require links to advertise available bandwidth.

Why this answer

MPLS TE with RSVP-TE requires that links advertise reservable bandwidth so that the Constrained Shortest Path First (CSPF) algorithm can compute paths that satisfy bandwidth constraints. Without reservable bandwidth advertised via IGP extensions (e.g., OSPF TE or IS-IS TE), RSVP-TE cannot reserve resources along the path.

Exam trap

Cisco often tests the misconception that LDP is required for MPLS TE with RSVP-TE, but RSVP-TE can distribute labels independently, making LDP optional.

Practice this question →

28

MCQmedium

In an IOS XR system, CPU and memory resources are allocated per line card. What is the primary reason for this design?

A.To reduce hardware cost by sharing resources

B.To simplify software licensing

C.To centralize management in the route processor

D.To ensure that a failure on one card does not impact others

AnswerD

Independent resources provide fault isolation.

Why this answer

Distributed architecture with per-card allocation improves scalability and fault isolation. It does not directly reduce cost or simplify management; instead, it enhances performance and resilience.

Practice this question →

29

MCQhard

A service provider is deploying network slicing for 5G services. Which slice type is characterized by low latency and high reliability for applications like autonomous driving?

A.FMC

B.eMBB

C.mMTC

D.uRLLC

AnswerD

uRLLC provides low latency and high reliability.

Why this answer

uRLLC (Ultra-Reliable Low-Latency Communications) is designed for latency-critical and reliable applications.

Practice this question →

30

MCQeasy

Refer to the exhibit. A PE router configuration for VRF CUST1 is shown. What is the most likely result when a CE sends a route with RT 100:100?

A.The route causes a BGP session reset

B.The route is imported and installed in VRF

C.The route is imported but not advertised to other CEs

D.The route is received but not imported into VRF

AnswerD

Only routes with matching RT import are imported; RT 100:100 does not match.

Why this answer

The VRF CUST1 configuration does not include a route-target import statement for RT 100:100. Without a matching import RT, the PE router will receive the route from the CE but will not import it into the VRF. The route is received (BGP update is accepted) but not installed in the VRF routing table, making option D correct.

Exam trap

Cisco often tests the distinction between BGP receiving a route (which always happens) and importing it into a VRF (which requires a matching import RT), leading candidates to mistakenly think any route from a CE is automatically placed into the VRF.

How to eliminate wrong answers

Option A is wrong because receiving a route with a non-matching RT does not cause a BGP session reset; BGP session resets are triggered by configuration changes or keepalive failures, not by route attributes. Option B is wrong because the route is not imported into the VRF; import requires a matching route-target import statement under the VRF address-family. Option C is wrong because the route is not imported at all, so it cannot be advertised to other CEs; only routes successfully imported into the VRF are eligible for export to other CEs based on export RTs.

Practice this question →

31

MCQeasy

Which access technology in a service provider network uses a passive optical splitter to distribute signals to multiple customers, with typical downstream speeds up to 2.5 Gbps?

A.Metro Ethernet

B.GPON

C.DSL

D.Cable (DOCSIS)

AnswerB

GPON uses passive optical splitters to distribute signals to multiple customers.

Why this answer

GPON is a point-to-multipoint fiber access technology using passive optical splitters, providing downstream speeds up to 2.5 Gbps and upstream up to 1.25 Gbps.

Practice this question →

32

MCQeasy

Which Cisco automation tool is designed for service modeling with YANG and provides lifecycle management of network services?

A.Cisco APIC

B.Cisco Prime Infrastructure

C.Cisco DNA Center

D.Cisco Network Services Orchestrator (NSO)

AnswerD

NSO provides YANG-based service modeling and lifecycle management.

Why this answer

Cisco NSO (Network Services Orchestrator) uses YANG models and NETCONF to manage service lifecycle.

Practice this question →

33

MCQeasy

A service provider is implementing MPLS L3VPN for a customer. The customer requires that routes from two different VPNs be imported into a single VRF. Which feature should be used?

A.Route Reflector

B.Route Target (RT) import/export

C.Route Distinguisher (RD)

D.BGP extended community

AnswerB

RT import/export is used to control which routes are imported into a VRF.

Why this answer

Route Target (RT) import/export is the correct feature because it controls which routes from which VPNs are imported into a given VRF. By configuring multiple RT import statements on a single VRF, the provider can selectively import routes from two different VPNs, enabling inter-VPN route sharing without merging the VPNs themselves.

Exam trap

Cisco often tests the distinction between RD (uniqueness) and RT (route selection), leading candidates to mistakenly choose RD when the question asks about importing routes from multiple VPNs into one VRF.

How to eliminate wrong answers

Option A is wrong because a Route Reflector is a BGP optimization tool used to reduce iBGP peering within an AS, not a mechanism for importing routes into a VRF. Option C is wrong because a Route Distinguisher (RD) is used to make IPv4 prefixes unique across VPNs (preventing route overlap), but it does not control route import/export behavior. Option D is wrong because BGP extended community is a generic category that includes RT, but the specific feature required is the Route Target import/export mechanism, not the broader community concept.

Practice this question →

34

Multi-Selecteasy

Which THREE protocols are used for label distribution in an MPLS network?

Select 3 answers

A.OSPF

B.LDP

C.IS-IS

D.BGP

E.RSVP

AnswersB, D, E

LDP is the most common label distribution protocol for MPLS.

Why this answer

LDP (Label Distribution Protocol) is a standardized protocol (RFC 5036) specifically designed for label distribution in MPLS networks. It operates by discovering LDP peers and exchanging label mappings for each FEC (Forwarding Equivalence Class), enabling label-switched path (LSP) establishment without requiring a routing protocol to carry label information.

Exam trap

Cisco often tests the distinction between routing protocols (OSPF, IS-IS) and label distribution protocols (LDP, RSVP, BGP), trapping candidates who assume that because a protocol is used in MPLS networks (e.g., OSPF for IGP), it also distributes labels.

Practice this question →

35

MCQmedium

A service provider offers Carrier Ethernet services using MPLS-TP in the access and aggregation layers. The network uses MPLS-TP tunnels with static LSPs and protection via 1:1 linear protection with APS. One customer reports intermittent connectivity issues on their E-LINE service. The operations team observes that the protection switchover is occurring frequently due to apparent signal failures on the working path. However, the physical layer shows no errors. The protection switching is configured with revertive mode. The working LSP has an RDI (Remote Defect Indication) configured. Upon further investigation, the team finds that the working LSP's OAM continuity check messages (CCMs) are being lost occasionally, triggering a protection switch. What is the most likely misconfiguration?

A.The CCM interval is too long, causing delayed detection.

B.The working path uses a higher MPLS-TP OAM rate than the protection path.

C.The protection path has a lower priority than the working path.

D.The CCM interval is too short, causing frequent false failures due to transient congestion.

AnswerD

Correct. A short interval makes the system overly sensitive, leading to false failure detection.

Why this answer

A short CCM interval makes the system sensitive to minor delays, causing false failures and frequent protection switches. A longer interval would reduce sensitivity but increase detection time. Priority and OAM rate differences are not typical causes.

Practice this question →

36

MCQeasy

Which Cisco platform is designed for high-capacity core/backbone routing with support for MPLS, Segment Routing, and large-scale BGP?

A.Cisco CRS

B.Cisco NCS 5500

C.Cisco 8000 series

D.Cisco ASR 9000

AnswerA

Correct. CRS is a core router.

Why this answer

Cisco CRS (Carrier Routing System) is a high-end core router designed for large service provider backbone networks, supporting MPLS, SR, and massive scale.

Practice this question →

37

MCQmedium

A service provider wants to implement Segment Routing in its MPLS core to simplify traffic engineering. What is the primary advantage of Segment Routing over traditional RSVP-TE?

A.No per-flow state on transit routers

B.Improved ECMP load balancing

C.Better support for Fast Reroute

D.Requires a central controller for path calculation

AnswerA

SR uses source routing; transit routers only need label forwarding.

Why this answer

Segment Routing (SR) eliminates the need for per-flow state on transit routers by encoding the path as a list of segment identifiers (SIDs) directly in the packet header. In contrast, RSVP-TE requires each transit router to maintain soft-state for every LSP, consuming memory and CPU. This state reduction simplifies network operation and scales better in large MPLS cores.

Exam trap

Cisco often tests the misconception that Segment Routing requires a central controller (like PCE) for path calculation, but in fact SR can use distributed IGP-based path computation or explicit SID lists without any controller.

How to eliminate wrong answers

Option B is wrong because both Segment Routing and RSVP-TE can leverage ECMP load balancing; SR does not inherently improve ECMP over RSVP-TE. Option C is wrong because Fast Reroute (FRR) is supported by both technologies (e.g., TI-LFA in SR, facility backup in RSVP-TE), and SR does not provide inherently better FRR. Option D is wrong because Segment Routing can operate without a central controller using distributed IGP or BGP-based path computation, whereas RSVP-TE typically requires a controller or head-end for explicit path calculation.

Practice this question →

38

MCQhard

In a carrier's network, MPLS-TE tunnels are used to steer traffic away from congested links. The operator configures a tunnel with a bandwidth of 200 Mbps and a dynamic path. The CSPF computation shows a path with sufficient bandwidth, but the tunnel fails to come up. The RSVP neighbor is established. What is the most likely cause?

A.The tunnel destination is not reachable via IGP

B.The path message is rejected due to resource reservation failure

C.The tunnel interface is down

D.MPLS LDP is not configured

AnswerB

RSVP-TE reserves bandwidth; if not available, tunnel fails.

Why this answer

The tunnel fails to come up because the CSPF-computed path cannot reserve the requested 200 Mbps bandwidth. Even though the path has sufficient bandwidth on paper, the RSVP resource reservation process may fail due to a lack of available bandwidth at the exact time of reservation, or due to a mismatch in bandwidth pool configuration (e.g., global vs. subpool). Since the RSVP neighbor is established, the issue is specifically with the reservation step, not with reachability or LDP.

Exam trap

Cisco often tests the distinction between CSPF path computation (which only checks link metrics and TE attributes) and RSVP resource reservation (which performs actual bandwidth admission control), leading candidates to incorrectly assume that a successful CSPF computation guarantees the tunnel will come up.

How to eliminate wrong answers

Option A is wrong because the RSVP neighbor is already established, which implies IGP reachability to the tunnel destination is present; RSVP relies on IGP routes to send Path messages. Option C is wrong because the tunnel interface being down would prevent any RSVP signaling, but the RSVP neighbor is established, indicating the interface is operationally up. Option D is wrong because MPLS LDP is not required for MPLS-TE tunnels; RSVP-TE handles label distribution for TE tunnels, and LDP is used for non-TE LSPs.

Practice this question →

39

MCQhard

A service provider is using NSO for service orchestration. Which protocol does NSO use to communicate with network devices for configuration?

A.NETCONF

B.SNMP

C.RESTCONF

D.CLI scripting

AnswerA

NSO uses NETCONF for device configuration.

Why this answer

NSO uses NETCONF as the primary protocol for device configuration, leveraging YANG models.

Practice this question →

40

MCQhard

Refer to the exhibit. An engineer has configured an SR-TE policy. What is required for this policy to be used for traffic steering?

A.Static routing

B.IGP with segment routing

C.BGP with color extended community

D.OSPF with opaque LSA

AnswerC

BGP routes with a color community matching the policy's color will steer traffic onto that policy.

Why this answer

An SR-TE policy uses a color extended community to identify the policy's color and its associated endpoint. BGP distributes these color extended communities, enabling headend routers to match traffic to the correct SR-TE policy for steering. Without BGP carrying the color extended community, the policy cannot be dynamically selected for traffic engineering.

Exam trap

Cisco often tests the misconception that IGP segment routing alone is sufficient for SR-TE policy steering, but the color extended community is exclusively carried by BGP, not by the IGP.

How to eliminate wrong answers

Option A is wrong because static routing does not interact with SR-TE policy selection; SR-TE policies are dynamically steered via BGP color extended communities, not static routes. Option B is wrong because while IGP with segment routing (e.g., IS-IS or OSPF) distributes prefix-SIDs and adjacency-SIDs, it does not carry the color extended community required to bind traffic to an SR-TE policy. Option D is wrong because OSPF opaque LSAs are used for traffic engineering extensions (e.g., OSPF-TE) but do not propagate the color extended community needed for SR-TE policy steering.

Practice this question →

41

MCQmedium

A service provider is deploying EVPN-VXLAN in its data center to provide Layer 2 and Layer 3 overlay services. The underlay uses an eBGP-based CLOS fabric with spine and leaf switches. The leaf switches act as VTEPs and run EVPN for MAC/VXLAN advertisement. One of the tenants, a financial customer, requires that their traffic between two leaf-connected servers is always forwarded through a firewall for inspection, even when the servers are on the same leaf. The firewall is connected to a service leaf. The architect proposes using EVPN integrated routing and bridging (IRB) with asymmetric IRB. However, traffic between two VMs on the same leaf is bypassing the firewall. Which architectural change ensures that all inter-VM traffic within the same leaf goes through the firewall?

A.Implement a VXLAN tunnel from each leaf to the firewall and use policy-based forwarding (PBF) on the leaf to redirect inter-VM traffic to the firewall via the tunnel.

B.Configure a gateway on the firewall and use static routes on the leaf to forward traffic to the firewall.

C.Use EVPN symmetric IRB and ensure the firewall is attached as a Layer 2 extension.

D.Enable 'split-horizon' on the leaf switches to prevent direct forwarding.

AnswerA

Correct. PBF can redirect traffic to the firewall even for local traffic, ensuring inspection.

Why this answer

Implement a VXLAN tunnel from each leaf to the firewall and use policy-based forwarding (PBF) on the leaf to redirect inter-VM traffic to the firewall via the tunnel. This forces traffic to the firewall even for local traffic. Split-horizon prevents loops, not service insertion; static routes are not scalable; symmetric IRB still allows local bridging.

Practice this question →

42

MCQeasy

In IOS XR architecture, what is the role of the Secure Domain Router (SDR)?

A.It handles all packet forwarding in hardware.

B.It is used for OSPF only.

C.It provides isolation for routing protocols and forwarding tables.

D.It manages the admin plane for all line cards.

AnswerC

SDR creates separate routing domains.

Why this answer

An SDR provides a logical partitioning of router resources, allowing multiple independent virtual routers within a single physical chassis.

Practice this question →

43

MCQmedium

In EVPN, what is the function of the Ethernet Segment Identifier (ESI)?

A.It is used for load balancing among PEs.

B.It identifies a multi-homed device or network segment.

C.It uniquely identifies a customer MAC address.

D.It identifies a VXLAN tunnel.

AnswerB

ESI is used for multi-homing.

Why this answer

The ESI identifies a multi-homed device or network, enabling all-active redundancy and fast convergence.

Practice this question →

44

MCQhard

An SP is deploying network slicing for 5G services. They need to ensure ultra-reliable low-latency communication (uRLLC) slice has dedicated bandwidth and low latency. Which mechanism is best suited to guarantee performance for this slice?

A.Class of Service (CoS) marking on all traffic

B.MPLS Traffic Engineering with RSVP-TE

C.Flexible Algorithm (Flex-Algo) in IGP

D.DiffServ with EF PHB

AnswerC

Correct. Flex-Algo can compute paths with low-latency constraints for uRLLC slices.

Why this answer

Network slicing using dedicated resources via Flex-Algo or resource reservation can guarantee performance. Flex-Algo allows IGP to compute paths based on constraints like latency, providing dedicated paths for uRLLC.

Practice this question →

45

MCQhard

A service provider uses BGP communities to influence routing policies. An administrator wants to prevent a specific prefix from being advertised to any external AS. Which BGP community should be applied?

A.NO_ADVERTISE

B.INTERNET

C.LOCAL_AS

D.NONE

E.NO_EXPORT

AnswerE

NO_EXPORT prevents advertisement to any eBGP peer, which is exactly what is needed.

Why this answer

The NO_EXPORT community (well-known community 0xFFFFFF01) tells the router not to advertise the prefix to any external BGP peer (eBGP), but allows it to be advertised within the same AS (iBGP). This matches the requirement to prevent the prefix from being advertised to any external AS, as NO_EXPORT is specifically designed to keep routes confined to the local autonomous system.

Exam trap

Cisco often tests the distinction between NO_EXPORT and NO_ADVERTISE, where candidates mistakenly choose NO_ADVERTISE because they think 'no advertisement' means 'no external advertisement,' but NO_ADVERTISE blocks all advertisements (including iBGP), while NO_EXPORT only blocks eBGP advertisements.

How to eliminate wrong answers

Option A (NO_ADVERTISE) is wrong because it prevents the prefix from being advertised to any BGP peer at all, including iBGP peers within the same AS, which is more restrictive than needed. Option B (INTERNET) is wrong because it is a well-known community (0xFFFFFF00) that means 'advertise this route to the Internet' (i.e., no restriction), which is the opposite of what is required. Option C (LOCAL_AS) is wrong because it prevents advertisement to peers in the same confederation sub-AS but allows advertisement to external ASes, which does not meet the requirement.

Option D (NONE) is wrong because it is not a valid BGP community value; BGP communities are 32-bit values, and 'NONE' is not defined in RFC 1997 or any standard.

Practice this question →

46

MCQmedium

A service provider needs to offer L3VPN services with customer isolation. Which technology is used to maintain separate routing tables for different customers on a single PE router?

A.VLAN

B.Route distinguisher (RD)

C.VRF

D.MPLS labels

AnswerC

VRF creates separate routing tables.

Why this answer

VRF (Virtual Routing and Forwarding) instances provide separate routing tables per customer, ensuring isolation in L3VPN.

Practice this question →

47

MCQmedium

Which MEF Carrier Ethernet service type is used for a rooted-multipoint topology, where a single root site communicates with multiple leaf sites but leaf sites cannot communicate directly?

A.E-Access

B.E-LAN

C.E-Tree

D.E-Line

AnswerC

E-Tree is rooted-multipoint.

Why this answer

E-Tree (Ethernet Tree) is a rooted-multipoint service where the root can communicate with leaves, but leaves cannot communicate with each other.

Practice this question →

48

MCQmedium

You are a network engineer at a service provider that offers L3VPN services. A customer complains that their VPN traffic is intermittently dropping. The network uses OSPF as the IGP, LDP for label distribution, and MP-BGP for VPNv4 route exchange. The PE routers are connected to two core routers (P1 and P2) in a redundant design. Upon investigation, you find that the BGP next-hop for some VPN prefixes is set to the loopback interface of the remote PE, but the route to that loopback is sometimes unreachable due to a flapping link between P1 and P2. The IGP converges, but the BGP prefixes take longer to recover. What is the most likely cause of the intermittent drops?

A.The OSPF network type is incorrectly set to point-to-point

B.The BGP timers are set too low, causing premature route withdrawal

C.BGP next-hop tracking is not enabled, causing BGP to rely on IGP convergence only

D.The LDP session between the PEs is down

AnswerC

NHT allows BGP to react quickly to IGP next-hop changes.

Why this answer

The intermittent drops occur because BGP next-hop tracking (NHT) is not enabled. Without NHT, BGP relies solely on IGP convergence to detect reachability changes for the BGP next-hop (the remote PE loopback). When the link between P1 and P2 flaps, OSPF converges quickly, but BGP does not immediately re-evaluate its next-hop reachability; it waits for the next BGP scan interval (default 60 seconds) or until a BGP update is received.

This delay causes the VPN prefixes to remain installed with an unreachable next-hop, leading to traffic drops until BGP eventually withdraws or re-advertises the routes.

Exam trap

Cisco often tests the misconception that BGP automatically reacts to IGP changes instantly, when in fact without NHT, BGP relies on periodic scanning, causing a delay that leads to traffic drops during transient IGP failures.

How to eliminate wrong answers

Option A is wrong because OSPF network type set to point-to-point would affect adjacency formation and LSA flooding, but it does not directly cause BGP to delay recovery after IGP convergence; the issue is about BGP next-hop reachability timing, not OSPF network type. Option B is wrong because setting BGP timers too low (e.g., keepalive/hold timers) would cause premature session resets, not intermittent drops tied to a flapping IGP link; the problem is BGP not reacting to IGP changes, not BGP session instability. Option D is wrong because the LDP session between PEs is not required for VPNv4 route exchange; LDP is used for label distribution within the MPLS core, and the PE-to-PE LDP session is not a standard design—LDP runs between directly connected LSRs, not between PEs across the core.

Practice this question →

49

MCQeasy

A service provider is designing a new MPLS core network and needs to choose a routing protocol that supports traffic engineering and fast convergence. Which protocol should be used?

A.RIP

B.EIGRP

C.OSPF

D.IS-IS

AnswerD

IS-IS supports MPLS TE and provides fast convergence, making it ideal for SP core.

Why this answer

IS-IS is the correct choice because it natively supports MPLS Traffic Engineering (TE) via IS-IS TE extensions (RFC 5305) and offers fast convergence through mechanisms like IS-IS Fast Flooding and LSP throttling. Unlike OSPF, IS-IS operates directly over Layer 2, making it more scalable and robust in large service provider core networks, and it avoids the need for a separate flooding domain for TE.

Exam trap

Cisco often tests the misconception that OSPF is the only link-state protocol suitable for MPLS TE, but the trap is that IS-IS is actually the more common choice in service provider cores due to its native TE support and superior scalability in hierarchical designs.

How to eliminate wrong answers

Option A is wrong because RIP is a distance-vector protocol with slow convergence and no support for traffic engineering or MPLS TE extensions. Option B is wrong because EIGRP is a Cisco-proprietary protocol that lacks native MPLS TE support and is not designed for the hierarchical, scalable core networks required by service providers. Option C is wrong because while OSPF supports MPLS TE via OSPF TE extensions (RFC 3630), it requires a separate opaque LSA type 10 flooding domain and has higher CPU overhead for TE link-state advertisements compared to IS-IS, making IS-IS the preferred choice in many service provider designs.

Practice this question →

50

MCQhard

A network engineer is designing a Layer 2 VPN using EVPN with MPLS data plane. The customer requires all-hub multipoint connectivity with optimal multicast replication. Which EVPN route type is used to advertise multicast group membership?

A.Route Type 3 (Inclusive Multicast Ethernet Tag)

B.Route Type 2 (MAC/IP Advertisement)

C.Route Type 4 (Ethernet Segment)

D.Route Type 6 (Selective Multicast Ethernet Tag)

AnswerD

Used to advertise multicast group membership for selective replication.

Why this answer

Route Type 6 (Selective Multicast Ethernet Tag) is used in EVPN to advertise multicast group membership for selective multicast replication. This allows the provider edge (PE) routers to build optimal multicast trees for specific groups, enabling efficient all-hub multipoint connectivity with EVPN-MPLS data plane.

Exam trap

Cisco often tests the distinction between inclusive (Route Type 3) and selective (Route Type 6) multicast, and the trap here is assuming that Route Type 3 is used for all multicast scenarios, when in fact Route Type 6 is required for optimal group-specific replication.

How to eliminate wrong answers

Option A is wrong because Route Type 3 (Inclusive Multicast Ethernet Tag) advertises an inclusive multicast service, meaning all traffic is flooded to all PEs in the broadcast domain, which does not support selective or optimal multicast replication. Option B is wrong because Route Type 2 (MAC/IP Advertisement) is used to advertise MAC and IP addresses for host reachability, not multicast group membership. Option C is wrong because Route Type 4 (Ethernet Segment) is used for multi-homing scenarios to advertise Ethernet segment identifiers and redundancy group information, not multicast group membership.

Practice this question →

51

MCQmedium

A service provider is deploying a new MPLS core network and needs a router platform that supports high-scale MPLS forwarding and offers a modular operating system. Which Cisco platform is best suited for this role?

A.Cisco ASR 9000

B.Cisco CRS

C.Cisco 8000 series

D.Cisco NCS 5500

AnswerB

The CRS is a core router supporting high-scale MPLS and IOS XR.

Why this answer

The Cisco CRS is a carrier-grade router designed for the core/backbone with high MPLS scalability and IOS XR modularity. ASR 9000 is more for aggregation, NCS for edge/aggregation.

Practice this question →

52

MCQmedium

In IOS XR, what is the primary purpose of the commit/rollback configuration model?

A.To automatically back up configurations to a remote server

B.To enforce role-based access control

C.To apply changes atomically and roll back if needed

D.To verify configuration syntax before applying

AnswerC

This is the core of the commit/rollback model.

Why this answer

The commit/rollback model allows changes to be applied atomically and rolled back if errors occur, ensuring configuration consistency.

Practice this question →

53

MCQeasy

What is the main benefit of using Q-in-Q (802.1ad) in metro Ethernet networks?

A.Increases the number of available VLANs

B.Simplifies routing

C.Provides encryption

D.Reduces latency

AnswerA

Q-in-Q expands VLAN space.

Why this answer

Q-in-Q allows multiple customer VLANs to be encapsulated within a service provider VLAN, increasing scalability.

Practice this question →

54

MCQeasy

Which network architecture model separates the control plane and data plane in a way that allows for centralized control and distributed forwarding?

A.SDN architecture

B.MPLS architecture

C.VPN architecture

D.QoS architecture

AnswerA

SDN centralizes control while keeping forwarding distributed.

Why this answer

Software-Defined Networking (SDN) architecture explicitly separates the control plane from the data plane, centralizing network intelligence in a controller while leaving packet forwarding to distributed switches and routers. This decoupling enables programmatic, centralized control of the network, with the controller (e.g., OpenDaylight, Cisco APIC) making forwarding decisions and pushing flow entries to devices via protocols like OpenFlow or OpFlex. The result is a logically centralized brain with physically distributed forwarding, which is the defining characteristic of SDN.

Exam trap

Cisco often tests the misconception that MPLS or VPN architectures inherently separate control and data planes, but they do not centralize control—they still rely on distributed protocols like LDP or MP-BGP, which is the key distinction from SDN.

How to eliminate wrong answers

Option B is wrong because MPLS architecture does not separate the control and data planes for centralized control; instead, it uses a distributed control plane (e.g., LDP, RSVP-TE) where each router independently builds its label forwarding table, and forwarding is still distributed. Option C is wrong because VPN architecture (e.g., MPLS Layer 3 VPN) relies on a distributed control plane using MP-BGP to exchange VPN routes, with each PE router making independent forwarding decisions; it does not centralize control. Option D is wrong because QoS architecture is a set of mechanisms (e.g., classification, policing, shaping) that operate within the data plane and control plane of existing devices, but it does not fundamentally separate the two planes for centralized control.

Practice this question →

55

MCQmedium

In an MPLS-based service provider core network, the aggregation layer typically connects to the core backbone. Which technology is primarily used at the aggregation layer to scale Ethernet services for many customers while preserving VLAN separation?

A.IEEE 802.1ah (MAC-in-MAC)

B.IEEE 802.3ad (Link Aggregation)

C.IEEE 802.1x (Port-based Network Access Control)

D.Q-in-Q (IEEE 802.1ad)

AnswerD

Q-in-Q double-tags Ethernet frames to scale VLANs per customer.

Why this answer

Q-in-Q (802.1ad) allows service providers to stack a customer VLAN tag on top of a service VLAN tag, enabling scalable customer separation in metro Ethernet networks.

Practice this question →

56

Multi-Selectmedium

Which THREE of the following are required components for implementing MPLS Layer 3 VPN (L3VPN) in a service provider network? (Choose three.)

Select 3 answers

A.MP-BGP between PE routers to exchange VPNv4 routes

B.VRF configuration on PE routers to separate customer routes

C.MPLS forwarding enabled on all core routers

D.IBGP between PE and P routers for label distribution

E.VRF configuration on P routers

AnswersA, B, C

MP-BGP between PE routers is mandatory for MPLS L3VPN because it carries VPNv4 routes that include both the IPv4 prefix and the Route Distinguisher, enabling unique global identification of overlapping customer address spaces. This satisfies the requirement for a control-plane protocol that can separate and distribute per-VPN routing information across the provider backbone.

Why this answer

MP-BGP (Multiprotocol BGP) is essential for carrying VPNv4 routes between PE routers. It uses address family VPNv4 to transport customer IPv4 prefixes along with their Route Distinguisher (RD) and Route Target (RT) attributes, enabling the separation and distribution of multiple customer VPNs across the MPLS core.

Exam trap

Cisco often tests the misconception that P routers require VRF configuration or that IBGP is used for label distribution between PE and P routers, when in fact P routers only need MPLS forwarding and LDP for label exchange.

Practice this question →

57

Multi-Selecthard

Which TWO are correct about network slicing? (Choose two.)

Select 2 answers

A.Network slicing is only applicable to the 5G core network.

B.Network slicing requires a separate physical infrastructure for each slice.

C.Each slice can have its own dedicated bandwidth and latency guarantees.

D.Slices can be optimized for different service types such as eMBB, uRLLC, and mMTC.

E.Network slicing eliminates the need for QoS mechanisms.

AnswersC, D

Correct. Slices provide resource isolation.

Why this answer

Network slicing divides a physical network into multiple virtual networks, each with dedicated resources. Slices can be tailored for specific services like eMBB, uRLLC, mMTC. They are not limited to 5G core but also include transport.

Practice this question →

58

Multi-Selectmedium

Which TWO statements about IOS XR architecture are correct? (Choose two.)

Select 2 answers

A.Configuration changes in IOS XR take effect immediately without a commit.

B.The admin plane in IOS XR is used for customer VPN configuration.

C.Each routing protocol runs as an independent process in IOS XR.

D.IOS XR runs a monolithic kernel where all protocols share the same memory space.

E.IOS XR supports a commit/rollback configuration model.

AnswersC, E

Correct. Process separation enhances stability.

Why this answer

IOS XR uses distributed OS with process separation, and a commit/rollback model for configuration. It does not have a monolithic kernel; each protocol is a separate process. The admin plane is separate from SDRs.

Practice this question →

59

MCQmedium

An SP is using Cisco ASR 9000 routers with IOS XR. They need to apply a configuration change and ensure that if the change causes issues, it can be easily reverted. Which IOS XR feature supports this?

A.Configuration replace

B.Synchronization to standby

C.Commit/rollback

D.Archive and restore

AnswerC

Correct. The commit/rollback model allows safe configuration changes.

Why this answer

IOS XR uses a commit/rollback configuration model. Changes are staged in a candidate configuration and committed; if issues arise, rollback to a previous commit is possible.

Practice this question →

60

MCQmedium

Which Cisco platform is best suited for the core/backbone role of a large service provider network, offering high scalability and MPLS forwarding capacity?

A.Cisco ASR 1000

B.Cisco CRS

C.Cisco ASR 9000

D.Cisco NCS 5500

AnswerB

CRS is a high-end core router.

Why this answer

Cisco CRS (Carrier Routing System) is designed for the core with high capacity and MPLS capabilities.

Practice this question →

61

MCQeasy

Which Cisco SP router platform runs IOS XR and is designed for the aggregation layer with high-density 10GE/100GE interfaces?

A.Cisco ISR 4000

B.Cisco ASR 9000

C.Cisco CRS

D.Cisco NCS 5500

AnswerB

ASR 9000 is the correct aggregation platform.

Why this answer

The Cisco ASR 9000 series is optimized for the aggregation layer with dense 10GE/100GE ports and runs IOS XR.

Practice this question →

62

Multi-Selecteasy

Which TWO access technologies are considered fiber-based solutions for service provider access networks? (Select two.)

Select 2 answers

A.WiMAX

B.Cable (DOCSIS)

C.XGS-PON

D.DSL

E.GPON

AnswersC, E

XGS-PON is a symmetric 10G PON.

Why this answer

GPON and XGS-PON are fiber-based PON technologies.

Practice this question →

63

Multi-Selecthard

A multicast service provider is designing an IPv4 PIM Sparse Mode (PIM-SM) network with multiple RPs. The network must support Anycast RP using MSDP. Which THREE statements are correct regarding this design?

Select 3 answers

A.Anycast RP allows multiple RPs to share the same IP address, providing redundancy and load balancing

B.Auto-RP must be used to distribute the RP information to all routers

C.MSDP peering is required between the anycast RP routers to exchange active source information

D.MSDP is only required if the network uses Source-Specific Multicast (SSM)

E.IGMPv3 is needed on the last-hop routers to support SSM if used together with Anycast RP

AnswersA, C, E

The same IP is configured as RP on multiple routers; MSDP ensures consistency.

Why this answer

Options A, C, and E are correct. Option A: Anycast RP uses the same IP address on multiple RPs, providing redundancy and load balancing. Option C: MSDP peering is required between the anycast RPs to exchange active source information.

Option E: IGMPv3 is needed on last-hop routers to support Source-Specific Multicast (SSM) if used together with Anycast RP. Option B is incorrect: Auto-RP is not required; Anycast RP can work with static RP assignments. Option D is incorrect: MSDP is used for Anycast RP, not specifically for SSM; SSM does not require MSDP.

Practice this question →

64

MCQhard

A service provider wants to provide point-to-point Ethernet services with strict SLAs. Which technology should they use?

A.VPWS

B.EVPN

C.L3VPN

D.VPLS

AnswerA

VPWS/pseudowire is point-to-point.

Why this answer

VPWS (Virtual Private Wire Service) or pseudowire provides a point-to-point Ethernet connection over MPLS.

Practice this question →

65

MCQeasy

A network engineer is troubleshooting an OSPF issue in a service provider network. The network uses OSPFv2 with multiple areas. Routers in area 0 are able to ping each other, but routers in area 1 cannot reach routers in area 2. All routers are OSPF-enabled and have correct network type configurations. What is the most likely cause?

A.Missing or misconfigured ABRs between area 1 and area 0, or area 2 and area 0

B.Mismatched OSPF area IDs on routers in area 1 and area 2

C.Lack of BGP peering between ABRs

D.OSPF network type mismatch preventing adjacency formation

AnswerA

Inter-area routing must go through area 0; without proper ABRs, areas cannot exchange routes.

Why this answer

In OSPFv2, inter-area communication must traverse area 0 (the backbone). Routers in area 1 and area 2 can only reach each other if Area Border Routers (ABRs) exist between each non-backbone area and area 0, and those ABRs are correctly configured and have full adjacencies. Since area 0 routers can ping each other but area 1 and area 2 cannot, the most likely cause is a missing or misconfigured ABR on either side, preventing the exchange of Type 3 summary LSAs between the areas.

Exam trap

Cisco often tests the misconception that OSPF areas can communicate directly without the backbone, leading candidates to overlook the mandatory role of ABRs and area 0 in inter-area routing.

How to eliminate wrong answers

Option B is wrong because mismatched OSPF area IDs on routers within area 1 and area 2 would prevent them from forming adjacencies with each other, but the issue is about inter-area reachability, not intra-area connectivity; area IDs are locally significant per interface and do not need to match across different areas. Option C is wrong because BGP peering between ABRs is not required for OSPF inter-area routing; OSPF uses its own LSAs (Type 3) to propagate routes between areas, and BGP is a separate routing protocol typically used for external route exchange, not for OSPF inter-area connectivity. Option D is wrong because the question explicitly states that all routers have correct network type configurations, and a network type mismatch would prevent adjacency formation locally, not specifically cause a failure only between area 1 and area 2 while area 0 remains functional.

Practice this question →

66

MCQhard

Refer to the exhibit. What is the significance of the entry with 'Pop Label'?

A.It indicates a merge operation

B.It indicates the penultimate hop popping (PHP)

C.It indicates the label is removed at this router

D.It indicates an error

AnswerB

PHP removes the label before sending to the egress.

Why this answer

In MPLS, the 'Pop Label' entry in a forwarding table indicates the Penultimate Hop Popping (PHP) operation. PHP is a standard behavior (RFC 3031) where the penultimate router removes the MPLS label before forwarding the packet to the egress LSR, reducing the egress router's processing load. This is explicitly signaled via the 'implicit-null' label (label value 3) in LDP or RSVP-TE.

Exam trap

Cisco often tests the distinction between 'Pop Label' (PHP) and a generic label removal at the egress router, tricking candidates into thinking any label pop is the same as PHP, when in fact PHP specifically occurs at the penultimate hop.

How to eliminate wrong answers

Option A is wrong because a merge operation (e.g., in MPLS-TE or LSP merging) combines multiple incoming labels into a single outgoing label, not a pop operation. Option C is wrong because while the label is indeed removed at this router, the 'Pop Label' entry specifically denotes PHP, not a generic label removal at any hop (e.g., the egress router also removes labels but uses 'explicit-null' or no label). Option D is wrong because 'Pop Label' is a valid and intentional forwarding action, not an error condition.

Practice this question →

67

Multi-Selecthard

When configuring EVPN VPWS, which TWO parameters must match between the two endpoints of the pseudowire?

Select 2 answers

A.EVI (Ethernet VPN Instance)

B.Route-target

C.ESI (Ethernet Segment Identifier)

D.VLAN ID of the attachment circuit

E.IMET group address

AnswersA, B

Correct. The EVI must match between endpoints as it defines the EVPN instance.

Why this answer

In EVPN VPWS, two parameters must match between endpoints: the EVI (Ethernet VPN Instance) must match because it defines the EVPN instance and the Route Distinguisher. The Route-target must also match because it ensures that routes are imported/exported correctly between the endpoints. The ESI (Ethernet Segment Identifier) is local to each PE and does not need to match; it identifies the local segment for split-horizon and DF election purposes.

Exam trap

A common misconception is that ESI must match, but ESI identifies the local segment and can differ. The key matching parameters are EVI and Route-target.

Practice this question →

68

MCQmedium

In a BGP/MPLS IP VPN, which technique ensures that customer traffic from different VPNs remains isolated on the same PE router?

A.Virtual Routing and Forwarding (VRF)

B.Route Target (RT)

C.MPLS labels

D.Route Distinguisher (RD)

AnswerA

VRF maintains separate routing and forwarding tables per VPN.

Why this answer

VRF (Virtual Routing and Forwarding) provides separate routing tables per VPN on a PE router. MP-BGP carries VPN routes with labels, but isolation is achieved by VRF.

Practice this question →

69

MCQhard

A network architect is designing a Segment Routing (SR) network for a service provider with a requirement for fast convergence upon node failure. The network uses IS-IS as the IGP with segment routing extensions. Which design choice BEST ensures that the network can achieve sub-50ms convergence without relying on any signaling protocol beyond the IGP?

A.Deploy BFD with static routes for fast detection

B.Configure RSVP-TE with Fast Reroute on all label-switched paths

C.Enable TI-LFA (Topology Independent Loop-Free Alternate) on all ISIS interfaces

D.Use LDP with LDP FRR and path protection

AnswerC

TI-LFA computes backup paths using only IGP information (IS-IS with segment routing extensions), ensuring sub-50ms convergence without any additional signaling protocol, making it the best choice.

Why this answer

TI-LFA (Topology Independent Loop-Free Alternate) provides sub-50ms convergence by precomputing backup paths using only the IGP (IS-IS with SR extensions), without requiring any additional signaling protocol. Option A is wrong because BFD with static routes offers fast detection but does not provide a backup path automatically; it must be combined with a protection mechanism like FRR. Option B is wrong because RSVP-TE Fast Reroute relies on RSVP signaling and TE tunnels, which are beyond the IGP-only requirement.

Option D is wrong because LDP is a separate signaling protocol that requires LDP FRR and path protection, again adding signaling overhead beyond the IGP.

Practice this question →

70

Multi-Selecthard

Which THREE of the following are benefits of using EVPN over traditional VPLS for L2VPN services? (Select three.)

Select 3 answers

A.Integrated L2 and L3 services (e.g., IRB)

B.Supports only point-to-point pseudowires

C.Multi-homing support with Ethernet Segment Identifier (ESI)

D.BGP-based control plane for MAC/VXLAN distribution

E.Eliminates the need for VPLS

AnswersA, C, D

EVPN can provide L2 and L3 services.

Why this answer

EVPN offers BGP control plane, multi-homing with ESI, and integrated L2/L3 services.

Practice this question →

71

MCQeasy

A service provider wants to offer a point-to-point Ethernet service between two customer sites with a defined bandwidth and performance guarantee, according to MEF standards. Which Carrier Ethernet service type is appropriate?

A.E-LAN

B.E-Line

C.E-Access

D.E-Tree

AnswerB

E-Line provides point-to-point Ethernet connectivity.

Why this answer

E-Line (Ethernet Line) is a point-to-point service defined by MEF for Carrier Ethernet.

Practice this question →

72

MCQmedium

In an IS-IS segment routing network, after the global 'segment-routing mpls' configuration, which IS-IS configuration is mandatory for label allocation?

A.mpls label protocol sr

B.segment-routing mpls under router isis

C.prefix-sid under the loopback interface

D.is-type level-1-2

AnswerB

This command is required to enable segment routing label allocation within the IS-IS process.

Why this answer

The global 'segment-routing mpls' command enables MPLS Segment Routing on the device, but it does not automatically enable label allocation under IS-IS. The mandatory IS-IS configuration to trigger label allocation is 'segment-routing mpls' under the 'router isis' process. Without this sub-mode command, IS-IS will not allocate MPLS labels for prefixes, even if prefix-SIDs are configured on interfaces.

Exam trap

Cisco often tests that candidates confuse the global 'segment-routing mpls' command with the IS-IS sub-mode 'segment-routing mpls' command, leading them to think the global command alone is sufficient for label allocation.

How to eliminate wrong answers

Option A is wrong because 'mpls label protocol sr' is used to specify the label distribution protocol as Segment Routing on an interface, but it is not required for IS-IS label allocation; IS-IS uses its own signaling for SR-MPLS. Option C is wrong because 'prefix-sid' under the loopback interface assigns a Segment ID to a prefix, but it is not mandatory for label allocation; labels can be allocated dynamically without explicit prefix-SIDs, and the mandatory step is enabling SR-MPLS under IS-IS. Option D is wrong because 'is-type level-1-2' defines the IS-IS level, which is unrelated to label allocation; SR-MPLS works with any IS-IS level configuration.

Practice this question →

73

MCQmedium

In EVPN, what is the purpose of Ethernet Segment Identifier (ESI)?

A.To identify a VXLAN tunnel

B.To assign a VLAN ID to a customer

C.To enable MPLS label distribution

D.To uniquely identify an Ethernet segment for multi-homing

AnswerD

ESI is key for multi-homing in EVPN.

Why this answer

ESI is used to identify a multi-homed site or Ethernet segment for all-active or single-active redundancy and to prevent loops.

Practice this question →

74

MCQeasy

What is the purpose of the 'mpls ldp autoconfig' command on an interface?

A.Enable MPLS forwarding

B.Enable LDP on all interfaces

C.Disable LDP on the interface

D.Automatically configure LDP on the interface

AnswerD

This command enables LDP automatically on the interface.

Why this answer

The 'mpls ldp autoconfig' command is used on an interface to automatically enable LDP on that interface for all IPv4 address families configured under the OSPF process. This eliminates the need to manually configure 'mpls ldp' on each interface, simplifying deployment in large-scale networks where LDP should be enabled on all OSPF-enabled interfaces.

Exam trap

Cisco often tests the distinction between 'mpls ldp autoconfig' (which enables LDP on OSPF interfaces automatically) and 'mpls ip' (which enables MPLS forwarding on an interface), leading candidates to confuse the purpose of the command.

How to eliminate wrong answers

Option A is wrong because 'mpls ldp autoconfig' does not directly enable MPLS forwarding; MPLS forwarding is enabled globally with 'mpls ip' or per interface with 'mpls ip', while this command specifically triggers LDP neighbor discovery and label exchange. Option B is wrong because the command does not enable LDP on all interfaces; it only enables LDP on interfaces that are part of the OSPF process under which the command is configured, not on all interfaces in the router. Option C is wrong because the command enables LDP on the interface, not disables it; to disable LDP on an interface, the command 'no mpls ldp autoconfig' or 'mpls ldp igp autoconfig disable' would be used.

Practice this question →

75

MCQmedium

What is the role of Network Services Orchestrator (NSO) in service provider automation?

A.To encrypt data plane traffic

B.To provide real-time traffic monitoring

C.To replace the routing protocol decision process

D.To orchestrate service provisioning across multiple devices

AnswerD

NSO orchestrates services end-to-end.

Why this answer

NSO provides service lifecycle management by modeling services with YANG and configuring devices via NETCONF.

Practice this question →

Page 1 of 4 · 232 questions totalNext →

Ready to test yourself?

Try a timed practice session using only Architecture questions.

Start 20-question session