350-501 Practice Test 40 — 15 Questions

Question 1

In IOS XR, each routing protocol runs as a separate process. What is the primary benefit of this architecture?

Accepted Answer

It allows each protocol to be upgraded independently without a system reboot.. IOS XR's modular architecture runs each routing protocol (BGP, OSPF, ISIS, etc.) as an independent process with its own memory space. This isolation means a protocol can be restarted, upgraded, or have its configuration changed without rebooting the router or affecting other protocols, delivering hitless software upgrades and fault containment.

Answer

It simplifies configuration by combining all protocols into a single file.

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It reduces memory consumption by sharing code between processes.

Answer

It improves forwarding performance by dedicating CPU cores to each protocol.

Question 2

Which multicast RP model is recommended for large-scale networks to provide redundancy and load sharing?

Accepted Answer

Anycast-RP. Anycast-RP is recommended for large-scale networks because it allows multiple RPs to share the same IP address, providing redundancy and load sharing without requiring dynamic RP discovery protocols. This model uses MSDP (Multicast Source Discovery Protocol) or PIM (Protocol Independent Multicast) to synchronize multicast state between RPs, ensuring that sources and receivers can register with the nearest RP for optimal path selection.

Answer

Auto-RP

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BSR

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Static RP

Question 3

An SP is implementing CGNAT to conserve IPv4 addresses. For legal compliance, they must log all NAT translations with timestamps and source/destination information. Which CGNAT feature should be enabled?

Accepted Answer

NAT logging. NAT logging (specifically Carrier-Grade NAT logging, often via syslog or NetFlow/IPFIX) records every translation event with timestamp, inside local IP:port, outside global IP:port, and destination IP:port. This is the feature that satisfies legal/regulatory requirements (e.g., lawful intercept, data retention) to trace which subscriber used a given public IP and port at a given time. Without it, CGNAT's many-to-one translation makes attribution impossible.

Answer

Destination NAT

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Port block allocation

Answer

ALG support

Question 4

A network engineer needs to automate configuration of multiple Cisco routers and wants to use a protocol that supports both datastore operations and selective retrieval of configuration. Which protocol should be used?

Accepted Answer

NETCONF. NETCONF (RFC 6241) is the correct choice because it is designed specifically for network configuration management, supporting full datastore operations (e.g., , , ) and selective retrieval of configuration data using subtree or XPath filtering. This aligns directly with the engineer's requirement for both datastore operations and selective retrieval.

Answer

SNMPv3

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gRPC

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OpenFlow

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RESTCONF

Question 5

Which TWO are benefits of model-driven telemetry over SNMP polling?

Accepted Answer

Supports structured data models (YANG). Option A is correct because model-driven telemetry uses structured, standardized YANG data models to define exactly what data is streamed, giving consistent, schema-based, machine-parsable output rather than the flat, vendor-specific MIB/OID structures used by SNMP polling. Option B is correct because model-driven telemetry is push-based (the device streams data on a subscription, often over gRPC/TLS), eliminating the repeated request/response cycles and per-poll processing overhead that SNMP polling imposes on the device CPU. Option C is incorrect because telemetry does not inherently reduce the number of credentials needed; it typically still requires authentication (e.g., certificates or AAA) for the gRPC session. Option D is incorrect because model-driven telemetry requires modern devices and software that support YANG models and streaming telemetry, so legacy devices generally cannot use it without modification. Option E is incorrect because model-driven telemetry is not limited to XML; it commonly uses JSON, and encodings such as GPB (gRPC/protobuf) or JSON are typical, with XML being just one possible option.

Answer

Requires fewer credentials for access

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Works with legacy devices without modification

Answer

Uses XML exclusively

Question 6

An engineer configures model-driven telemetry on a Cisco XR router to send data to a collector. After configuring, the collector receives no data. The engineer verifies that the collector IP and port are reachable. What is the next step to troubleshoot?

Accepted Answer

Check that the sensor-group and destination-group are correctly associated and committed in the subscription. In model-driven telemetry on Cisco XR, a subscription must explicitly associate a sensor-group (which defines the data to collect) with a destination-group (which defines where to send it). If these are not correctly associated and committed, the router will not stream any telemetry data to the collector, even if the collector is reachable. The verification of reachability confirms the network path is fine, so the next logical step is to check the subscription configuration.

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Check if the YANG model is valid

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Verify that the router has a route to the collector

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Reboot the router

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Check the SNMP community strings

Question 7

Which THREE technologies or protocols are used to implement automated service provisioning in a Cisco service provider network?

Accepted Answer

Cisco NSO. Cisco NSO (option A) is a model-driven orchestration platform that automates provisioning of services across multivendor networks by using device models and service abstractions, making it a core technology for automated service provisioning. YANG (option C) is the data modeling language used to define the configuration and state data structures that NSO and other controllers consume, so it is essential for describing services and device models in an automated provisioning workflow. NETCONF (option E) is the XML-based protocol that carries YANG-modeled configuration changes to devices, enabling programmatic, transactional configuration delivery that underpins automated provisioning. SNMP (option B) is primarily used for monitoring and fault/performance management rather than model-driven configuration provisioning, so it does not belong here. RIP (option D) is a distance-vector routing protocol for IP reachability and has nothing to do with service provisioning automation.

Answer

SNMP

Answer

RIP

Question 8

Which THREE are benefits of using EVPN over traditional VPLS? (Choose three.)

Accepted Answer

MAC address learning over the control plane (MAC mobility). Option A is correct because EVPN distributes MAC reachability information through BGP control-plane advertisements (MAC/IP Advertisement routes), enabling control-plane MAC learning and MAC mobility, unlike VPLS which relies on data-plane flooding and learning. Option B is correct because EVPN uses MP-BGP as its control plane to distribute MAC and IP routes (and VXLAN/NVGRE or MPLS encapsulation information) via EVPN route types, providing scalable, policy-driven signaling that VPLS lacks. Option C is correct because EVPN supports all-active multihoming through Ethernet Segment Identifiers (ESI) and DF election, allowing a CE to connect to multiple PEs with load balancing and fast failover, whereas VPLS typically only supports single-active or active/standby multihoming. Option D is incorrect because EVPN actually requires BGP (MP-BGP with the EVPN address family), so it is not simpler in that sense. Option E is incorrect because EVPN does not inherently provide lower latency via MPLS label switching; latency depends on the underlying transport, and EVPN can run over VXLAN or MPLS alike.

Answer

Simpler configuration without BGP

Answer

Lower latency due to MPLS label switching

Question 9

An operator is deploying EVPN-VPWS over an MPLS network. Which component uniquely identifies a multihomed Ethernet segment in EVPN?

Accepted Answer

Ethernet Segment Identifier (ESI). The Ethernet Segment Identifier (ESI) is a 10-byte value that uniquely identifies a multihomed Ethernet segment in EVPN — that is, a set of links from one or more CEs to two or more PEs that form a single logical segment. It is carried in the Ethernet A-D route and is the key field used for all-active or single-active multihoming procedures. Without a unique ESI, PEs cannot coordinate DF election or aliasing for the segment.

Answer

Ethernet Tag ID

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Route Distinguisher (RD)

Answer

MPLS Label

Question 10

An MPLS Traffic Engineering LSP fails to establish. The RSVP signaling shows 'PathErr: Admission Control Failure'. The link has sufficient bandwidth but the headend reports a lack of resources. What is the most likely cause?

Accepted Answer

The RSVP bandwidth is not configured on the interface or is set to 0. The 'PathErr: Admission Control Failure' with 'lack of resources' despite sufficient link bandwidth indicates that RSVP has no reservable bandwidth on the interface. This occurs when the 'ip rsvp bandwidth' command is missing or set to 0, preventing RSVP from admitting any LSP even if the physical link has capacity. The headend correctly reports the failure because the interface-level RSVP resource pool is exhausted or unconfigured.

Answer

The tunnel is requesting more bandwidth than available on any path

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The MPLS forwarding table is corrupted

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The headend router does not have the correct destination address

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The LSP is configured with a strict explicit path that is impossible

Question 11

A service provider is implementing Segment Routing over IPv6 (SRv6) in their core. They want to provide path isolation for different services using SRv6 SIDs. Which SID structure is used to encode both the locator and the function?

Accepted Answer

The SID is divided into locator and function (and optionally arguments).. In SRv6, the SID is encoded as a 128-bit IPv6 address that is explicitly divided into three parts: the Locator (identifies the node or prefix), the Function (identifies the specific behavior or instruction), and optionally Arguments (additional parameters). This structure allows path isolation by assigning unique locator/function combinations per service, enabling per-service steering without additional label stacks.

Answer

The SID uses a separate label stack for function encoding.

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The SID is an IPv6 address without any encoding.

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The SID consists of a prefix only.

Question 12

An engineer is configuring BGP Graceful Shutdown (GSHUT) for maintenance on a router. Which BGP attribute is set to trigger the graceful shutdown behavior?

Accepted Answer

Community GRACEFUL_SHUTDOWN. BGP GSHUT uses a specific community (GRACEFUL_SHUTDOWN, value 65535:0) to signal peers that the session is being gracefully shut down, causing them to depreference the routes.

Answer

MED to maximum

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AS_PATH prepend

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Local preference to 0

Question 13

A service provider is migrating from LDP to Segment Routing. What is the correct order of operations to ensure uninterrupted MPLS forwarding?

Accepted Answer

Enable SR on each router one by one while LDP remains active, then remove LDP after SR is stable.. It follows the recommended migration strategy of running LDP and Segment Routing (SR) in parallel. By enabling SR on each router one by one while LDP remains active, MPLS forwarding continues uninterrupted via LDP until SR is fully deployed and stable. Once SR is verified on all routers, LDP can be safely removed without causing any forwarding black holes.

Answer

Enable SR on all routers simultaneously.

Answer

Configure IS-IS SR extensions on all routers, then disable LDP.

Answer

Disable LDP first to free labels, then enable SR.

Question 14

A service provider operates a large MPLS network with Segment Routing (SR) and BGP-LS enabled on all routers. They have deployed a centralized Path Computation Element (PCE) to compute SR-TE policies for optimal traffic engineering. The PCE is configured to receive the network topology via BGP-LS from a route reflector (RR). Recently, the PCE has been unable to compute paths for certain destinations, and logs show that the topology database is missing some links and nodes. The engineer verifies that all routers have BGP-LS configured and are peering with the RR. The RR's BGP table shows the BGP-LS NLRI received from all routers. However, the PCE sees only a subset of the topology. Which action should the engineer take to resolve the issue?

Accepted Answer

Configure the RR to send BGP-LS routes to the PCE. Verify that the RR has a BGP session with the PCE in the address-family link-state.. The PCE is not receiving the full topology because the Route Reflector (RR) is not sending BGP-LS routes to the PCE. The most likely cause is that the RR is not configured to advertise BGP-LS to the PCE. Option C is correct: the engineer should verify that the RR has a BGP session with the PCE in the address-family link-state and ensure that BGP-LS routes are being sent. Option A is wrong because BGP-LS relies on IGP for link-state information, but the issue is not with IGP visibility; the RR already receives BGP-LS from all routers. Option B is wrong because filtering out prefixes would reduce topology information, not solve missing data. Option D is wrong because the PCE does not need direct BGP-LS adjacency to each router; it can receive topology via the RR.

Answer

Check the IGP (OSPF/IS-IS) configuration on the routers. BGP-LS relies on IGP to obtain link-state information, and if IGP does not have full visibility, BGP-LS will not either.

Answer

Apply a prefix-list on the PCE to filter out unwanted BGP-LS prefixes, as the PCE may be overwhelmed.

Answer

Verify that the PCE itself has a BGP-LS adjacency to each router, bypassing the RR.

Question 15

Which TWO tasks are required when implementing segment routing in an MPLS network?

Accepted Answer

Configure the IGP (OSPF or IS-IS) with segment routing extensions. Option C is correct because segment routing relies on the IGP to distribute prefix-SID information, so OSPF or IS-IS must be configured with segment routing extensions (e.g., OSPFv2 SR extensions or IS-IS SR extensions) to advertise SIDs and build the SR topology. Option D is correct because MPLS forwarding must be enabled on every interface participating in segment routing so that labeled packets carrying SIDs can be forwarded along the SR path. Option A is not required because segment routing does not depend on RSVP-TE to establish LSPs; SR uses IGP-advertised SIDs instead of signaled paths. Option B is not a segment routing-specific requirement, since CEF is a general Cisco forwarding prerequisite rather than a task unique to SR implementation. Option E is not required because segment routing replaces LDP for label distribution, so enabling LDP on all routers and interfaces is unnecessary and can even conflict with SR-MPLS operation.

Answer

Configure RSVP-TE to establish LSPs

Answer

Enable CEF on all routers

Answer

Enable LDP on all routers and interfaces