350-501 Practice Test 32 — 15 Questions

Question 1

A service provider is implementing QoS policies on an access aggregation router. They want to shape traffic to a downstream DSLAM to 10 Mbps, but they do not want to exceed the shaping rate even if the line rate is higher. Which QoS tool should be used on the interface facing the DSLAM?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

Shaping. Shaping is the correct tool because it buffers excess traffic and smooths the output rate to a configured target (10 Mbps) without exceeding it, even if the physical line rate is higher. Unlike policing, shaping does not drop or re-mark packets when the rate is exceeded, ensuring the downstream DSLAM receives traffic at or below the shaped rate.

Answer

Queuing

Answer

Marking

Answer

Policing

Question 2

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

Accepted Answer

To enable process separation and fault isolation. A Secure Domain Router (SDR) in IOS XR partitions a single physical router into multiple independent logical routers, each with its own control plane, routing processes, and configuration. This provides process separation and fault isolation, so a failure or misconfiguration in one SDR does not affect the others. It is the IOS XR mechanism for multi-tenancy and administrative separation.

Answer

To encrypt control plane traffic

Answer

To provide a secure management plane

Answer

To aggregate multiple physical routers

Question 3

Which THREE are characteristics of EVPN? (Choose three.)

Accepted Answer

Supports all-active multi-homing. EVPN supports all-active multi-homing (Option B), meaning a CE device can connect to multiple PEs that all forward traffic simultaneously, providing load balancing and faster convergence than traditional active/standby multi-homing. It also supports multi-homing with an Ethernet Segment Identifier (Option C), where the ESI uniquely identifies the Ethernet segment across the participating PEs so they can coordinate DF election and aliasing. EVPN uses BGP as its control plane signaling protocol (Option D), specifically MP-BGP with EVPN NLRI (AFI 25, SAFI 70) to distribute MAC/IP reachability and IMET routes. Option A is wrong because EVPN provides both L2VPN (E-LAN, E-LINE) and L3VPN services, not only L2VPN. Option E is wrong because EVPN does not use LDP for pseudowire signaling; that is characteristic of VPWS/VPLS using LDP-based signaling, whereas EVPN relies on BGP.

Answer

Provides only L2VPN services

Answer

Uses LDP for pseudowire signaling

Question 4

An SP implements Carrier-Grade NAT (CGNAT) to conserve IPv4 addresses. For legal compliance, what additional function must be enabled to log subscriber IP-port mappings?

Accepted Answer

NAT logging (syslog or other). Carrier-Grade NAT (CGNAT) is used by service providers to conserve public IPv4 addresses by multiplexing many subscribers behind a small pool of public IPs. For legal compliance (e.g., lawful intercept, abuse investigation), the SP must be able to map a public IP and port back to the specific subscriber at a given time. NAT logging (via syslog or other mechanisms) records these IP-port-subscriber bindings and is the required additional function.

Answer

Port allocation algorithm (deterministic or random)

Answer

Application Layer Gateway (ALG) support

Answer

Deep Packet Inspection (DPI)

Question 5

In an IS-IS network, a service provider wants to achieve fast convergence using Partial Route Computation (PRC). Which of the following events triggers a PRC instead of a full SPF?

Accepted Answer

An IP prefix is withdrawn from a directly connected network. Partial Route Computation (PRC) is triggered when only IP prefix reachability information changes, without any change to the IS-IS topology (adjacencies or router roles). Withdrawing an IP prefix from a directly connected network changes only the reachability entry in the link-state database, so the router runs PRC to update the RIB without recomputing the entire SPF tree. This is a key optimization in IS-IS for fast convergence in large networks.

Answer

A router's system ID changes

Answer

An LSP with a new fragment arrives

Answer

A new adjacency is formed between two routers

Question 6

A service provider is designing an OSPF network with multiple areas. Which three area types prevent Type 5 LSAs from entering the area (choose three)?

Accepted Answer

Totally stubby area. Stub areas block Type 5 LSAs and rely on a default route. Totally stubby areas block both Type 4 and Type 5 LSAs, also using a default route. NSSAs block Type 5 LSAs but allow Type 7 LSAs, which are translated to Type 5 at the ABR. Thus, all three area types prevent Type 5 LSAs from entering the area.

Answer

Backbone area

Answer

Standard area

Question 7

Which THREE are common causes of QoS misconfiguration on PE routers? (Choose three.)

Accepted Answer

Applying a policy-map in the wrong direction (input vs output).. Applying a policy-map in the wrong direction (input vs output) is a common QoS misconfiguration because QoS actions like shaping, policing, and queuing are direction-specific. For example, shaping is typically applied on the egress interface to control outbound traffic, while policing can be applied inbound to rate-limit incoming traffic. Misapplying a policy-map (e.g., attaching a shaper to the input direction) will either be ignored by the router or cause unexpected behavior, leading to QoS failures.

Answer

Using the 'bandwidth percent' command in a class that also has a priority queue.

Answer

Insufficient bandwidth on the subscriber line.

Question 8

In IS-IS, which type of metric uses 24 bits (wide) to allow higher link bandwidth values and is required for TE support?

Accepted Answer

Wide metric. Wide metric, because IS-IS wide metrics use a 24-bit field that supports much larger link bandwidth values than the classic 6-bit narrow metric, and they are required for Traffic Engineering (TE) support since TE extensions rely on the wider metric encoding. Narrow metrics (option C) are limited to 6 bits and cannot represent high-bandwidth links, while the extended metric (option A) is not the standard IS-IS term for this 24-bit metric. The TE metric (option D) is a separate concept used for TE path selection and is not the 24-bit metric type itself.

Answer

Extended metric

Answer

Narrow metric

Answer

TE metric

Question 9

An SP wants to secure management access to IOS XR routers. Which two measures should be implemented? (Choose two.)

Accepted Answer

Implement AAA with TACACS+. Option A (Implement AAA with TACACS+) is correct because AAA centralizes authentication, authorization, and accounting for management access, and TACACS+ provides per-command authorization and encrypted (full-payload) communication, which is the recommended approach for securing administrative access to IOS XR routers. Option D (Use SSH for remote access) is correct because SSH encrypts the management session and provides strong authentication, replacing insecure cleartext protocols like Telnet for CLI access. Option B is wrong because Telnet transmits credentials and session data in cleartext, making it unsuitable for secure management. Option C is wrong because SNMPv2c uses community strings sent in cleartext and lacks the cryptographic security of SNMPv3, so it does not secure management access. Option E is wrong because disabling all logging removes audit trails and event visibility, which weakens security monitoring rather than improving it.

Answer

Enable Telnet for remote access

Answer

Use SNMPv2c for monitoring

Answer

Disable all logging

Question 10

A service provider is deploying BGP PIC (Prefix Independent Convergence) for edge routers. What is the primary benefit of BGP PIC?

Accepted Answer

It provides fast convergence by pre-installing backup paths in the FIB. BGP PIC provides fast failover by precomputing backup paths in the forwarding table, enabling sub-second convergence upon failure, independent of the number of prefixes.

Answer

It reduces the number of BGP updates during a flap

Answer

It reduces the memory usage on the router

Answer

It eliminates the need for BFD

Question 11

In Segment Routing for MPLS (SR-MPLS), which TLV is used in IS-IS to advertise the Node SID?

Accepted Answer

TLV 135. In IS-IS for SR-MPLS, the Node SID is advertised using TLV 135 (Extended IP Reachability) with the SR-MPLS SID/Label sub-TLV (sub-TLV 3). TLV 135 carries the prefix reachability information, and the sub-TLV attaches the SID to that prefix. TLV 149 (SR-MPLS SID/Label Binding TLV) is used for external prefixes or mapping server advertisements, not for directly attached Node SIDs.

Answer

TLV 232

Answer

TLV 22

Answer

TLV 149

Question 12

Which TWO of the following are characteristics of the IOS XR operating system architecture? (Select two.)

Accepted Answer

Commit/rollback configuration model. Option B is correct because IOS XR uses a commit-based configuration model: changes are staged in a candidate configuration and only take effect when the operator issues the commit command, with the ability to roll back to previous configurations. Option D is correct because IOS XR is a distributed operating system in which processes run in separate protected memory spaces, and control-plane functions are distributed across the route processor and line cards rather than sharing one monolithic image. Option A is incorrect because IOS XR does not apply configuration changes immediately; they require an explicit commit. Option C is incorrect because IOS XR is not a monolithic kernel with shared memory; it is built on a microkernel-style, modular architecture with process isolation. Option E is incorrect because line cards do not all run a single shared control-plane process; IOS XR distributes processes across nodes, with each line card running its own processes.

Answer

Configuration changes take effect immediately without commit

Answer

Monolithic kernel where all processes share memory

Answer

All line cards run a single control plane process

Question 13

Which protocol is used by NSO to communicate with network devices for configuration management?

Accepted Answer

NETCONF. NSO (Network Services Orchestrator) uses NETCONF as its primary protocol for configuration management because NETCONF provides a standardized, transaction-based mechanism for editing device configurations using YANG data models. This allows NSO to perform atomic, rollback-capable configuration changes across multiple network devices, which is essential for service orchestration.

Answer

gRPC

Answer

SNMP

Answer

HTTP

Question 14

Based on the exhibit, why is the route 10.10.10.0/24 from remote PE not installed in the VRF Customer-A on PE1?

Accepted Answer

The VRF imports route-target 200:200, but the route has RT 100:100. In MPLS L3VPN, route targets (RTs) control import and export of routes between VRFs. The VRF Customer-A on PE1 imports routes with RT 200:200, but the remote PE is exporting the route with RT 100:100. Since the RTs do not match, the route is not imported into the VRF. This is the reason the route is not installed.

Answer

The localpref is too low (100)

Answer

The MPLS label allocation failed on the remote PE

Answer

The route distinguisher on the VRF (100:1) does not match the remote RD

Question 15

A service provider wants to provide IPv6 connectivity over an existing MPLS IPv4 core using BGP extensions. Which technology should be used?

Accepted Answer

6PE. 6PE (IPv6 Provider Edge) uses BGP to carry IPv6 prefixes with an IPv4 next-hop over an MPLS core, avoiding the need for IPv6 in the core.

Answer

NAT64

Answer

Dual-stack

Answer

6VPE