350-501 Practice Test 5 — 25 Questions

Question 1

An engineer is configuring QoS on a service provider edge router to prioritize real-time traffic. Which queuing mechanism provides the lowest latency and jitter for voice traffic?

Accepted Answer

LLQ. LLQ (Low Latency Queuing) is the correct choice because it combines a strict priority queue with CBWFQ, ensuring that voice traffic is always served before any other queue. This strict priority scheduling minimizes both latency and jitter for real-time traffic, which is critical for voice quality.

Answer

FIFO

Answer

CBWFQ

Answer

WRED

Question 2

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?

Accepted Answer

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

Answer

The same EVI is used on both PEs.

Answer

The ESI is all-zeros.

Answer

The MTU mismatch on the attachment circuits.

Question 3

Which TWO statements about MPLS label operations are correct? (Choose two.)

Accepted Answer

At the ingress LSR, a label is pushed onto the packet.. Option B is correct because the ingress LSR (ingress edge router of the MPLS domain) imposes a label on the incoming IP packet, an operation known as a label push, before forwarding it into the MPLS core. Option E is correct because an intermediate LSR (transit router) performs a label swap, replacing the incoming label with the outgoing label found in its LFIB (Label Forwarding Information Base) entry for that FEC. Options A, C, and D are incorrect: label operations in the MPLS core are driven by the incoming label value, not the IP destination address; the ingress LSR pushes rather than pops labels; and the egress LSR pops (removes) the label rather than swapping it.

Answer

Label operations are performed based on the IP destination address.

Answer

At the ingress LSR, the label is popped.

Answer

At the egress LSR, a label is swapped.

Question 4

Which TWO of the following are characteristics of MPLS L3VPN architecture? (Choose two.)

Accepted Answer

Each customer has a separate VRF on the PE router. Option B is correct because in an MPLS L3VPN, each customer (or VPN) is mapped to a separate VRF on the PE router, which isolates customer routing tables and allows overlapping IP address spaces to coexist. Option E is correct because customer IP prefixes are distributed between PE routers as VPNv4 routes via MP-BGP (multiprotocol BGP) using route targets and route distinguishers to maintain VPN membership. Option A is incorrect because MPLS L3VPN traffic is not forwarded by label switching alone; PE routers perform IP lookup within the VRF and impose labels, and the first hop may be IP-based. Option C is incorrect because LDP is not strictly required in the core; label distribution can be provided by RSVP-TE, SR (Segment Routing), or other mechanisms. Option D is incorrect because P routers only maintain the global IGP routing table and forward labeled packets; they do not hold per-VPN routing tables, which reside on PE routers.

Answer

All traffic is forwarded using MPLS label switching only

Answer

LDP is required for label distribution in the core

Answer

The P routers maintain a full routing table for each VPN

Question 5

An SP uses NSO for automation. Which TWO protocols can NSO use as southbound interfaces to communicate with network devices? (Choose two.)

Accepted Answer

RESTCONF. RESTCONF is a southbound interface that NSO uses to communicate with network devices. It is a RESTful protocol that uses HTTP methods (GET, POST, PUT, DELETE) to access YANG-defined data models, making it suitable for modern programmable devices. NSO leverages RESTCONF to configure and manage devices that support this protocol, providing a standardized, stateless interface for automation.

Answer

gRPC

Answer

SNMP

Answer

HTTP

Question 6

A service provider is deploying BGP PIC (Prefix Independent Convergence) to improve convergence after a link failure. Which mechanism does BGP PIC leverage to achieve fast failover?

Accepted Answer

It pre-installs a backup path in the routing table and forwarding plane.. BGP PIC uses backup paths that are pre-installed in the RIB/FIB. When the primary path fails, traffic is immediately switched to the backup path without waiting for BGP re-convergence.

Answer

It decreases the BGP update timer to propagate withdrawals faster.

Answer

It reduces the BGP hold timer to detect failures faster.

Answer

It uses BFD to detect failures and triggers BGP to recompute routes immediately.

Question 7

Which component of an MPLS-TE FRR (Fast Reroute) configuration provides protection for the next-hop node by bypassing it?

Accepted Answer

Node protection. In MPLS-TE Fast Reroute, node protection provides a bypass tunnel that avoids the next-hop node entirely, protecting against the failure of that node (not just the link). This is achieved by pre-computing a backup path that skips the next-hop router, so if the node fails, traffic is rerouted around it. Link protection, by contrast, only bypasses the link between the local router and the next hop.

Answer

Path protection

Answer

Link protection

Answer

Bandwidth protection

Question 8

In SRv6, which endpoint behavior is used for decapsulation and forwarding to a Layer 3 VPN IPv4 destination, removing the outer IPv6 header?

Accepted Answer

End.DT4. End.DT4 is the SRv6 endpoint behavior that decapsulates the outer IPv6 header and forwards the inner IPv4 packet into a specific IPv4 VPN routing table (the L3VPN IPv4 table). It is the SRv6 equivalent of MPLS VPN's per-VRF IPv4 lookup after label disposition, making it the correct choice for L3VPN IPv4 decapsulation.

Answer

End.X

Answer

End.DT6

Answer

End.DT2U

Question 9

A service provider is migrating its MPLS core from LDP to Segment Routing with MPLS data plane (SR-MPLS). The network currently uses TE tunnels with RSVP-TE for traffic engineering. Which technology can the provider use to continue performing traffic engineering after the migration without requiring RSVP-TE?

Accepted Answer

SR-TE. C is correct because Segment Routing Traffic Engineering (SR-TE) allows the service provider to perform traffic engineering without RSVP-TE by using segment lists (label stacks) to steer traffic along explicit paths. SR-TE leverages the IGP (OSPF or IS-IS) to distribute segment IDs (SIDs) and uses a centralized controller or headend node to compute and enforce TE policies, eliminating the need for RSVP-TE's per-flow signaling and state maintenance.

Answer

LDP

Answer

MPLS-TE (RSVP-TE)

Answer

BGP-LU

Question 10

An SP network engineer is reviewing a QoS configuration on a PE router. The policy-map uses a class for voice with the 'priority' command, and a class for video with 'bandwidth remaining percent 30'. What is the purpose of the 'bandwidth remaining percent' command?

Accepted Answer

It allocates a percentage of the bandwidth left after priority queues are served.. The 'bandwidth remaining percent' command allocates a percentage of the bandwidth that remains after priority (LLQ) queues have been served. It is a CBWFQ mechanism that ensures non-priority classes share the leftover bandwidth proportionally, preventing starvation while still respecting the strict priority of voice traffic. This is why it is used for video alongside a priority class for voice — video gets a guaranteed share of what's left, not a hard cap.

Answer

It sets the maximum bandwidth for the class.

Answer

It guarantees a minimum bandwidth for the class.

Answer

It enables Weighted Random Early Detection on the class.

Question 11

During QoS troubleshooting, you capture traffic and see that DSCP markings are not being applied as configured. Which two common misconfigurations could cause this? (Choose two.)

Accepted Answer

The policy-map is not applied to the correct interface direction (input vs output). A policy-map must be applied in the correct direction (input or output) for the marking to take effect. If a marking policy is applied to the wrong direction, the packets will not be processed by the policy, and DSCP values will remain unchanged. This is a common misconfiguration when the intended marking should occur on ingress but the policy is applied to egress, or vice versa.

Answer

The policy-map is applied to a loopback interface

Answer

The marking is configured under the wrong policy-map

Answer

The device is running out of TCAM space

Question 12

Refer to the exhibit. A network engineer applies this policy on the PE-CE link. What is the expected behavior for VoIP traffic matching the access list?

Accepted Answer

VoIP traffic is given strict priority queuing with up to 30% bandwidth. The policy-map applies the 'priority' command to the VoIP class, which enables strict priority queuing (LLQ). The 'police cir percent 30' command limits the priority queue's bandwidth to 30% during congestion, ensuring VoIP traffic is always served first but cannot exceed the configured percentage. This matches option A exactly.

Answer

VoIP traffic is dropped if congestion occurs

Answer

VoIP traffic is shaped to 30% of bandwidth

Answer

VoIP traffic is queued in the default class with fair-queue

Question 13

Which TWO are characteristics of Segment Routing (SR-MPLS)? (Choose two.)

Accepted Answer

It relies on source routing. Option A is correct because SR-MPLS is fundamentally a source-routing architecture: the ingress node (headend) encodes the entire path as an ordered list of SIDs in the MPLS label stack, so intermediate nodes simply forward based on the top label without needing per-flow state. Option E is correct because Segment Routing is data-plane agnostic and can be instantiated over an MPLS data plane (SR-MPLS, using MPLS labels as SIDs) or over an IPv6 data plane (SRv6, using IPv6 addresses as SIDs), which is a defining characteristic of the SR architecture. Option B is incorrect because SR-MPLS does not require a centralized controller; distributed path computation via IGP (IS-IS/OSPF) extensions is sufficient, and a controller (e.g., PCE/SR-PCE) is optional for advanced TE. Option C is incorrect because SR-MPLS forwards based on the top MPLS label (SID) in the stack, not by performing a destination-IP lookup at each hop. Option D is incorrect because SR-MPLS explicitly removes the need for LDP; label/SID distribution is handled by IGP extensions (or BGP), making LDP unnecessary.

Answer

It requires a centralized controller for traffic engineering

Answer

It forwards packets based on destination IP address at each hop

Answer

It requires MPLS LDP for label distribution

Question 14

In Segment Routing, what is the role of the 'Prefix-SID'?

Accepted Answer

It identifies a prefix in the IGP. A Prefix-SID is a Segment Routing identifier bound to an IGP prefix. It allows forwarding along the shortest path computed by the IGP to that prefix. Therefore, it identifies a prefix in the IGP, not a specific adjacency or node.

Answer

It identifies a specific adjacency

Answer

It is used for service chaining

Answer

It identifies a specific node

Question 15

A service provider is deploying L3VPN using BGP/MPLS. Which mechanism ensures customer isolation in the provider network?

Accepted Answer

Virtual Routing and Forwarding (VRF). Virtual Routing and Forwarding (VRF) creates separate routing tables on the same physical router, ensuring that customer routes are isolated from one another. Each VRF maintains its own RIB and FIB, so packets from one customer cannot be forwarded using another customer's routing information. This is the fundamental mechanism for customer isolation in BGP/MPLS L3VPN.

Answer

Pseudowire

Answer

MP-BGP

Answer

MPLS labels

Question 16

A customer requires MPLS Layer 2 VPN connectivity between two sites using Pseudowire. Which control protocol is used to signal the pseudowire label?

Accepted Answer

LDP. B is correct because LDP (Label Distribution Protocol) is the standard control protocol used to signal pseudowire labels in MPLS Layer 2 VPNs. Specifically, the Targeted LDP (T-LDP) session between the two Provider Edge (PE) routers exchanges the Virtual Circuit (VC) label, which is the inner label used to identify the pseudowire. This is defined in RFC 4447 and is the default signaling mechanism for AToM (Any Transport over MPLS).

Answer

RSVP-TE

Answer

BGP

Answer

OSPF

Question 17

Refer to the exhibit. This JSON policy is used for Segment Routing Traffic Engineering. What is the purpose of the 'color' attribute?

Accepted Answer

It identifies a specific SR-TE policy to be used for traffic steering. In Segment Routing Traffic Engineering (SR-TE), the 'color' attribute is a 32-bit numerical value that, combined with the destination prefix, uniquely identifies an SR-TE policy. This allows traffic to be steered into a specific policy based on color, enabling advanced traffic engineering use cases such as multi-topology routing or service-level agreement (SLA) differentiation.

Answer

It sets the metric type for the path calculation

Answer

It defines the preference value for the candidate path

Answer

It specifies the link affinity constraint for the path

Question 18

Which TWO protocols are supported by a BNG (Broadband Network Gateway) for subscriber session establishment? (Choose two)

Accepted Answer

PPPoE. PPPoE (A) is correct because a BNG terminates PPPoE sessions, using PPP negotiation (LCP, authentication via PAP/CHAP, IPCP) to establish and manage each subscriber session over Ethernet access networks. IPoE (DHCP) (B) is also correct because a BNG supports IPoE subscriber sessions where DHCP (with Option 82 or similar) is used to assign addresses and trigger session creation, often with per-subscriber policies. IPSec (C) is a security protocol suite for VPNs, not a subscriber session establishment method on a BNG. L2TP (D) is a tunneling protocol often used with LAC/LNS architectures, not a native BNG subscriber session type. PPPoA (E) is used over ATM access, not supported as a BNG subscriber session establishment protocol in this context.

Answer

IPSec

Answer

L2TP

Answer

PPPoA

Question 19

An engineer is configuring MPLS-TE FRR for link protection. Which of the following options describes a 1:1 protection scheme where a dedicated detour LSP is created for each protected LSP?

Accepted Answer

Detour LSP for each protected LSP. In MPLS-TE Fast Reroute (FRR), a 1:1 protection scheme means a dedicated detour LSP is created for each protected LSP. This provides per-LSP backup, ensuring that if a link fails, traffic is immediately switched to the detour tunnel. Option C correctly describes this exact mechanism, where each protected LSP has its own pre-established detour path.

Answer

Shared mesh protection

Answer

Bypass tunnel protecting multiple LSPs

Answer

Node protection bypass tunnel

Question 20

In an MPLS network using LDP, which statement correctly describes the label distribution behavior for a given FEC?

Accepted Answer

Labels are advertised unsolicited to all neighbors, and all labels are retained even if not used (liberal label retention).. LDP uses downstream unsolicited mode by default, where each LSR advertises labels for all FECs to all neighbors without being asked, and liberal label retention stores all received labels even if not currently used.

Answer

Labels are advertised only in response to a request from an upstream neighbor (downstream on demand).

Answer

Labels are advertised unsolicited but only the best label for each FEC is retained (conservative label retention).

Answer

Labels are advertised only when the LSR has an outgoing label for the FEC (ordered label distribution).