350-501 Practice Test 37 — 15 Questions

Question 1

A service provider is implementing Segment Routing in an IS-IS network. Which TLV is used to advertise the Segment Routing Global Block (SRGB)?

Accepted Answer

TLV 242. In IS-IS Segment Routing, TLV 242 (Router Capability TLV) is used to advertise the Segment Routing Global Block (SRGB) and other SR capabilities. It is defined in RFC 8667 and carries sub-TLVs including the SRGB.

Answer

TLV 22

Answer

TLV 229

Answer

TLV 135

Question 2

In BGP/MPLS IP VPN (L3VPN), which component provides customer isolation by maintaining separate routing tables per customer?

Accepted Answer

VRF. A VRF (Virtual Routing and Forwarding) instance maintains a separate routing table per customer on the PE router, providing logical isolation of customer routes. Each VRF is associated with interfaces and BGP sessions, ensuring customer traffic is kept separate.

Answer

Route distinguisher (RD)

Answer

MPLS label

Answer

MP-BGP

Question 3

Which THREE statements are true regarding NSO's NED? (Choose three.)

Accepted Answer

NED can support NETCONF, SNMP, or CLI as southbound protocols. NSO's NED (Network Equipment Driver) is the component that abstracts the southbound communication between NSO and network devices. NEDs can use NETCONF, SNMP, or CLI as the southbound protocol to translate NSO's device-independent configuration into device-specific commands, enabling multi-vendor management.

Answer

NED automatically generates YANG models

Answer

NED is used for path computation in SR-TE

Question 4

In OSPFv3 (for IPv6), which of the following statements is true regarding OSPFv3 packet format and authentication?

Accepted Answer

OSPFv3 relies on IPsec for authentication and encryption.. OSPFv3 removed the authentication fields that existed in the OSPFv2 header and instead relies on IPsec (via the IPv6 Authentication Header and Encapsulating Security Payload) to provide authentication, integrity, and optional confidentiality. This design leverages IPv6's native security framework rather than duplicating it inside the routing protocol. IPsec AH provides authentication and integrity, while ESP can add encryption.

Answer

OSPFv3 does not support authentication.

Answer

OSPFv3 authenticates using the Authentication field in the OSPF header.

Answer

OSPFv3 uses the same authentication mechanisms as OSPFv2.

Question 5

In an OSPF network, an engineer wants to reduce the size of the routing table and prevent external routes from being advertised into an area. Which area type should be configured?

Accepted Answer

Stub area. A stub area does not allow AS-external LSAs (type 5), reducing routing table size. NSSA allows limited external routes via type 7 LSAs.

Answer

Totally stubby area

Answer

Backbone Area 0

Answer

NSSA

Question 6

An SP engineer is using YANG to model a service. Which statement correctly describes the use of a 'leafref' type?

Accepted Answer

It restricts the leaf value to match another leaf's value. Leafref references an existing leaf in the YANG data tree, ensuring consistency.

Answer

It performs data validation using XPath

Answer

It defines a new leaf with a default value

Answer

It allows multiple values to be selected

Question 7

In IS-IS, what is the purpose of the System ID portion of the NET address?

Accepted Answer

It identifies the router within the area. The System ID portion of the NET (Network Entity Title) in IS-IS is a 6-byte field that uniquely identifies the router within an area. It is analogous to a router ID in OSPF and is used to form the system's unique identifier in the IS-IS domain. The System ID must be unique within the area.

Answer

It identifies the area to which the router belongs

Answer

It indicates the routing protocol version

Answer

It specifies the ISO layer (SEL) for routing

Question 8

Which TWO BGP path attributes are considered before AS-path length in the default best-path selection process?

Accepted Answer

Weight. Weight (D) is evaluated first in the Cisco BGP best-path algorithm, before AS-path length, and it is locally significant with higher values preferred. Local Preference (E) is evaluated next, after Weight but still before AS-path length, and it is propagated within the AS with higher values preferred. Origin code (A) is checked after AS-path length, so it does not precede it. Community (B) is not a standalone best-path attribute in the standard selection order; it is used for route tagging and policy matching rather than direct comparison at that stage. MED (C) is evaluated after AS-path length, so it also does not come before it.

Answer

Origin code

Answer

Community

Answer

MED

Question 9

An SP uses traffic policing and shaping to manage bandwidth. Which statement best describes the difference between the two mechanisms?

Accepted Answer

Shaping buffers excess traffic to smooth bursts, while policing drops or re-marks excess traffic.. Traffic shaping buffers excess packets and delays them to smooth out bursts, ensuring that the traffic rate conforms to the configured policy. Traffic policing, on the other hand, drops or re-marks packets that exceed the rate limit, without buffering them. This is the fundamental difference between the two mechanisms.

Answer

Both mechanisms buffer excess traffic but policing uses a smaller buffer.

Answer

Shaping drops excess traffic while policing buffers it.

Answer

Policing buffers excess traffic while shaping drops it.

Question 10

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

Accepted Answer

Virtual Routing and Forwarding (VRF). 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.

Answer

Route Target (RT)

Answer

MPLS labels

Answer

Route Distinguisher (RD)

Question 11

Which THREE statements about implementing QoS in an MPLS VPN environment are correct? (Choose three.)

Accepted Answer

DSCP values can be set at the PE router to classify customer traffic into different classes.. On a PE router, DSCP values can be set or remarked to classify incoming customer traffic into distinct service classes. This classification is performed at the ingress edge of the MPLS VPN network, allowing the provider to apply appropriate per-hop behaviors (PHBs) before the traffic is label-switched.

Answer

QoS policies cannot be applied to MPLS interfaces due to label encapsulation.

Answer

802.1p CoS marking is preserved across the MPLS backbone by default.

Question 12

A network engineer is troubleshooting an MPLS TE tunnel that is not coming up. The tunnel is configured with a strict explicit path, and the path includes an interface that is currently down. Which action should the engineer take to allow the tunnel to use an alternative path?

Accepted Answer

Change the explicit path to 'loose' for the down interface.. Changing the explicit path from 'strict' to 'loose' for the down interface allows the MPLS TE tunnel to use an alternative next-hop that is reachable, even if the specified interface is down. A strict explicit path requires every hop to be directly connected, so a down interface prevents the tunnel from coming up. By making the hop loose, the router can route around the failed link using the IGP's best path to the next specified node.

Answer

Increase the path-option preference value.

Answer

Disable path protection on the tunnel.

Answer

Configure an affinity constraint to exclude the down interface.

Question 13

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

Accepted Answer

VPLS. VPLS (Virtual Private LAN Service) is the MPLS-based Layer 2 VPN technology that emulates an Ethernet LAN across the provider network, making all customer sites appear to be on the same broadcast domain. It uses pseudowires (typically signaled via LDP or BGP) to forward Ethernet frames between PE routers, and the PEs perform MAC learning to switch frames like a distributed switch. This multipoint any-to-any behavior is exactly what distinguishes VPLS from point-to-point Layer 2 services.

Answer

L3VPN

Answer

VPWS (Virtual Private Wire Service)

Answer

EVPN

Question 14

A service provider wants to offer a point-to-point Layer 2 Ethernet service between two customer sites with strict SLAs. The solution must use MPLS pseudowires. Which MEF service type aligns with this requirement?

Accepted Answer

E-Line. E-Line is the MEF service type that provides a point-to-point Ethernet connection between exactly two customer sites, which maps directly to an MPLS pseudowire (VPWS) carrying Ethernet frames. It is the only MEF service defined for a dedicated, point-to-point EVC with strict SLA guarantees.

Answer

E-Tree

Answer

E-Access

Answer

E-LAN

Question 15

Which congestion avoidance mechanism is used to prevent tail drop by selectively dropping packets from lower-priority flows before the queue becomes full?

Accepted Answer

WRED. WRED (Weighted Random Early Detection) is the congestion-avoidance mechanism that monitors average queue depth and probabilistically drops packets from lower-priority or non-ECN-marked flows before the queue hits 100%, preventing global synchronization and tail drop. It combines RED's early-drop behavior with IP precedence/DSCP weighting so higher-priority traffic is dropped less aggressively.

Answer

Policing

Answer

LLQ

Answer

CBWFQ