350-501 Practice Exam 3 — 20 Questions

Question 1

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?

Accepted Answer

Ethernet Segment Identifier (ESI). 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.

Answer

MPLS Traffic Engineering

Answer

BGP Link-State

Answer

VPLS with BGP autodiscovery

Question 2

An SP network uses NSO for service orchestration. Which component in NSO provides the abstraction layer to communicate with different device types using protocols like NETCONF or CLI?

Accepted Answer

NED. NEDs (Network Element Drivers) are plugins that translate NSO's service models to device-specific configurations.

Answer

YANG

Answer

RESTCONF

Answer

CDB

Question 3

Which YANG data modeling construct is used to restrict a leaf value to be a reference to another leaf in the data tree?

Accepted Answer

leafref. The 'leafref' type in YANG is used to restrict the value of a leaf to refer to another leaf in the data tree, enforcing referential integrity.

Answer

when

Answer

must

Answer

choice

Question 4

When DSCP markings are mapped to MPLS EXP bits at the ingress PE router, how many EXP values are available for traffic differentiation in the MPLS core?

Accepted Answer

8. MPLS EXP (now TC) is a 3-bit field, providing 8 possible values (0-7).

Answer

16

Answer

64

Answer

32

Question 5

Which two statements correctly describe the use of DSCP values in the DiffServ model? (Choose two.)

Accepted Answer

DSCP is a 6-bit field allowing 64 distinct values.. DSCP is a 6-bit field with 64 possible values. Per-hop behaviors (PHBs) like EF and AF are defined by DSCP values.

Answer

DSCP values are mapped to MPLS EXP bits at the egress PE.

Answer

DSCP values are used only for voice traffic.

Answer

DSCP value 0 indicates low latency traffic.

Question 6

In SRv6, which endpoint behavior is used for decapsulating the outer IPv6 header and performing an IPv4 lookup (e.g., for L3VPN)?

Accepted Answer

End.DT4. End.DT4 is the SRv6 endpoint behavior that decapsulates the outer IPv6 header and then performs a lookup in the IPv4 VPN table. End.DT6 is for IPv6, and End.DT2U is for L2VPN.

Answer

End.DT6

Answer

End.DT2U

Answer

End.DX4

Question 7

In SR-MPLS, when a router receives a packet with an MPLS label corresponding to an Adjacency SID, what operation does it perform?

Accepted Answer

It pops the label and forwards the packet out of the specific interface.. An Adjacency SID represents a specific link; when a router receives a packet with that label, it pops the label and forwards the packet out of the associated interface, because the Adjacency SID is a 'penultimate hop popping' type of SID.

Answer

It performs a recursive lookup in the FIB to determine the next hop.

Answer

It pushes an additional label and forwards.

Answer

It swaps the label with the next-hop label and forwards.

Question 8

Which TWO are benefits of using EVPN over traditional VPLS for L2VPN services? (Choose two.)

Accepted Answer

Provides MAC address learning via control plane. EVPN offers better control plane (BGP) and supports multi-homing with all-active load balancing.

Answer

Uses LDP for label distribution

Answer

Requires full mesh of pseudowires

Answer

Simpler configuration than VPLS

Question 9

An SP is designing a QoS policy for a customer with voice, video, and data traffic. Which queuing mechanism provides a strict priority queue for voice while ensuring other queues do not starve?

Accepted Answer

LLQ. Low Latency Queuing (LLQ) combines a strict-priority queue for delay-sensitive traffic like voice with CBWFQ for all other classes, ensuring voice gets absolute priority while remaining classes are serviced fairly so they do not starve. It is the Cisco-recommended mechanism for converged voice/video/data QoS designs.

Answer

WFQ

Answer

WRED

Answer

CBWFQ

Question 10

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

Accepted Answer

It provides isolation for routing protocols and forwarding tables.. An SDR provides a logical partitioning of router resources, allowing multiple independent virtual routers within a single physical chassis.

Answer

It handles all packet forwarding in hardware.

Answer

It is used for OSPF only.

Answer

It manages the admin plane for all line cards.

Question 11

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

Accepted Answer

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

Answer

It is used for load balancing among PEs.

Answer

It uniquely identifies a customer MAC address.

Answer

It identifies a VXLAN tunnel.

Question 12

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?

Accepted Answer

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

Answer

E-Access

Answer

E-LAN

Answer

E-Line

Question 13

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

Accepted Answer

Configuration changes are staged and committed atomically; rollback is supported.. The commit/rollback model applies changes atomically and allows reverting to previous configurations if needed.

Answer

It requires a reboot to apply changes.

Answer

Changes are applied immediately and cannot be undone.

Answer

It only applies to interface configurations.

Question 14

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

Accepted Answer

Integrated L2 and L3 services (e.g., IRB). EVPN offers BGP control plane, multi-homing with ESI, and integrated L2/L3 services.

Answer

Supports only point-to-point pseudowires

Answer

Eliminates the need for VPLS

Question 15

Which architecture feature of IOS XR ensures that a failure in one routing protocol process does not affect other processes on the same router?

Accepted Answer

Process separation with each protocol as a separate process. IOS XR's process separation model runs each routing protocol as an independent process with its own protected memory space. If one protocol process fails (e.g., OSPF crashes), the other processes (BGP, ISIS) continue running unaffected, providing fault isolation and preventing a single protocol failure from cascading across the router.

Answer

Admin plane vs default SDR

Answer

Commit/rollback configuration model

Answer

CPU and memory allocation per card

Question 16

Which MEF service type is used for multipoint-to-multipoint Ethernet connectivity, such as a corporate LAN extension across multiple sites?

Accepted Answer

E-LAN. E-LAN (Ethernet LAN) is the MEF service type that provides multipoint-to-multipoint Ethernet connectivity, allowing any site to communicate with any other site as if they were on the same LAN. It is the standard choice for corporate LAN extension across multiple locations. E-Line is point-to-point and E-Tree is rooted multipoint, so neither matches the multipoint-to-multipoint requirement.

Answer

E-Line

Answer

E-Tree

Answer

E-Access

Question 17

An SP uses Cisco ASR 9000 routers with IOS XR. Which statement correctly describes the commit/rollback configuration model in IOS XR?

Accepted Answer

Changes are staged in a candidate configuration and applied only after 'commit'; rollback to a previous commit is possible.. IOS XR uses a two-stage configuration model: changes are made in a candidate configuration and only take effect after the 'commit' command. The system maintains a rollback buffer of previous commits, allowing rollback to any of the last 10 committed configurations using 'rollback configuration' or 'load rollback changes'. This provides safe, transactional configuration changes.

Answer

Only 'commit replace' is supported; rollback requires manual re-entry.

Answer

The router automatically commits changes every 10 minutes.

Answer

Changes take effect immediately without commit; rollback is not supported.

Question 18

An SP network uses OSPF with RSVP-TE for traffic engineering. Which OSPF extension is required to advertise TE link parameters such as maximum reservable bandwidth?

Accepted Answer

OSPF Type 10 Opaque LSAs. OSPF TE extensions are defined in RFC 3630, which introduces the Opaque LSA (Type 9, 10, 11). Specifically, Type 10 Opaque LSAs carry TE information. The TE LSA is carried in an Opaque LSA of area scope (Type 10).

Answer

OSPF Type 7 LSAs

Answer

OSPF Type 11 Opaque LSAs

Answer

OSPF Type 5 LSAs

Question 19

A service provider wants to automate service provisioning using NSO. Which protocol is typically used by NSO to configure network devices?

Accepted Answer

NETCONF. Cisco NSO (Network Services Orchestrator) uses NETCONF as its primary southbound protocol to configure network devices, leveraging YANG data models for structured, transactional configuration. NETCONF's candidate/commit model aligns with NSO's intent-based automation approach.

Answer

CLI scripting

Answer

SNMP

Answer

RESTCONF

Question 20

An SP uses SR-PCE for traffic engineering. Which protocol does the SR-PCE use to communicate path computation requests and responses with path computation clients (PCCs)?

Accepted Answer

PCEP. PCEP (Path Computation Element Protocol) is used between PCCs (e.g., routers) and a PCE (e.g., SR-PCE) for path computation requests and responses.

Answer

BGP-LS

Answer

NETCONF

Answer

RESTCONF