350-501 Practice Test 16 — 15 Questions

Question 1

A service provider is migrating from LDP to Segment Routing (SR) in the core. They need to support MPLS forwarding without maintaining LDP sessions. Which SR data plane is appropriate?

Accepted Answer

SR-MPLS. Segment Routing with MPLS data plane (SR-MPLS) uses IGP to distribute labels, eliminating the need for LDP. SR-MPLS is the direct replacement for LDP in MPLS networks.

Answer

SRv6

Answer

LDP over RSVP

Answer

MPLS-TE with RSVP-TE

Question 2

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

Accepted Answer

Supports all-active multi-homing. EVPN uses BGP control plane, supports multi-homing with ESI, and can provide both L2 and L3 services. It does not use LDP for signaling; it uses BGP. VPLS is older.

Answer

Provides only L2VPN services

Answer

Uses LDP for pseudowire signaling

Question 3

A service provider is deploying a new metro Ethernet network and needs to support multiple customer VLANs over a single physical link without overlapping VLAN IDs. Which technology should be used at the access layer to achieve this?

Accepted Answer

Q-in-Q (802.1ad) double tagging. Q-in-Q (802.1ad) allows service providers to add an outer VLAN tag to customer frames, enabling customer VLAN separation even when their VLAN IDs conflict. This is commonly used in metro Ethernet networks for scalability.

Answer

VLAN translation

Answer

MAC-in-MAC (802.1ah)

Answer

VLAN trunking with 802.1Q

Question 4

A service provider has deployed a new MPLS L3VPN service for a customer with multiple sites. The customer reports intermittent voice quality issues during peak hours. The provider uses a DiffServ QoS model with MPLS EXP markings. The PE routers apply the following policy on the customer-facing interfaces:

policy-map CUSTOMER-OUT
 class VOICE
  priority percent 10
  set mpls experimental topmost 5
 class VIDEO
  bandwidth remaining percent 30
  set mpls experimental topmost 4
 class DATA
  bandwidth remaining percent 70
  set mpls experimental topmost 0

The core network has a simple policy that maps EXP 5 to PQ, EXP 4 to a low-latency queue, and EXP 0 to best effort. The provider monitors the network and finds that the PE-CE interfaces are not congested (average utilization is 40%), but the voice packets are experiencing jitter. The customer's voice traffic is about 5% of the link capacity. Which action is most likely to reduce the jitter?

Accepted Answer

Add a police command under the VOICE class to limit voice traffic to 5% and shape the priority queue.. The voice traffic is only 5% of link capacity, but the priority percent 10 command allows up to 10% of the link to be treated as priority. During peak hours, if other traffic (e.g., video or data) bursts and exceeds the remaining bandwidth, the priority queue can still be policed implicitly by the scheduler, but jitter arises because the priority queue is not rate-limited. Adding a police command under the VOICE class to limit voice to 5% and shaping the priority queue ensures that voice traffic does not exceed its actual rate, preventing microbursts that cause jitter in the priority queue.

Answer

Configure the core routers to map EXP 5 to a low latency queue instead of PQ.

Answer

Increase the priority percent to 20 for voice traffic.

Answer

Change the set mpls experimental topmost to set ip dscp ef for voice.

Question 5

Which TWO features are used to improve BGP convergence in an MPLS VPN environment?

Accepted Answer

Bidirectional Forwarding Detection (BFD). Bidirectional Forwarding Detection (BFD) provides sub-second failure detection for BGP sessions, reducing the time to detect a link or neighbor failure from seconds (default BGP keepalive/hold timers) to milliseconds. BGP Prefix Independent Convergence (PIC) pre-installs backup paths in the forwarding table, allowing traffic to be rerouted immediately upon failure without waiting for BGP to reconverge. Together, these features drastically improve BGP convergence in an MPLS VPN environment.

Answer

Route redistribution

Answer

Next-hop-self

Answer

BGP multipath

Question 6

Which OSPF area type does not allow external routes (Type 5 LSAs) but does allow inter-area routes and can have a default route injected?

Accepted Answer

Stub area. A stub area blocks Type 5 LSAs, and a default route is injected for external destinations.

Answer

Totally stubby area

Answer

Backbone area (Area 0)

Answer

Not-So-Stubby Area (NSSA)

Question 7

An SP is implementing IPv6 transition using MAP-T. Which encapsulation method does MAP-T use?

Accepted Answer

IPv4-IPv6 translation (NAT64-like). MAP-T (Mapping of Address and Port using Translation) uses IPv4-IPv6 translation (stateless NAT64-like) at the customer edge, not encapsulation.

Answer

MPLS label switching

Answer

IPv4 in IPv6 encapsulation

Answer

IPv6 in IPv4 encapsulation

Question 8

In BGP route selection, which attribute is considered before the MED when comparing routes from different ASes?

Accepted Answer

ORIGIN type. The BGP best path selection order is: weight, local pref, originated locally, AS_PATH length, ORIGIN, MED, etc. MED is considered after ORIGIN.

Answer

Local preference

Answer

Next-hop reachability

Answer

AS_PATH length

Question 9

An SP's core router experiences excessive packet drops on a congested link. The QoS policy uses CBWFQ with 4 queues. The drops occur only in the queue for a premium business class. Which is the most likely cause?

Accepted Answer

The premium class is configured with a police action that drops traffic when it exceeds the committed information rate.. The premium business class queue is experiencing excessive packet drops because a police action configured with a 'drop' exceed-action is discarding traffic that exceeds the committed information rate (CIR). Unlike congestion management (queuing), policing is a congestion avoidance mechanism that drops packets immediately when the traffic rate surpasses the configured CIR, regardless of the queue depth or available bandwidth. This explains why drops occur only in the premium class queue, as the policer is explicitly dropping excess packets before they even enter the CBWFQ scheduler.

Answer

The 'bandwidth remaining' command is missing from the policy-map.

Answer

The interface is using MLP with interleaving.

Answer

The queue is using tail-drop without WRED.

Question 10

A service provider is designing an OSPF network for both IPv4 and IPv6. Which two features are supported by OSPFv3 but not by OSPFv2? (Choose two.)

Accepted Answer

Support for IPv6. OSPFv3 runs over IPv6, supports multiple instances per link, and uses link-local addresses. OSPFv2 does not have these.

Answer

Virtual links

Answer

Authentication using MD5

Answer

Route redistribution

Question 11

Which BGP mechanism can reduce the number of iBGP sessions in a large SP network while preventing routing loops?

Accepted Answer

BGP route reflector. Route reflectors allow iBGP speakers to advertise routes learned from other iBGP peers, reducing full mesh requirements, and use cluster-id and originator-id to prevent loops.

Answer

BGP PIC

Answer

BGP confederation

Answer

BGP BFD

Question 12

In IS-IS, which type of router is responsible for routing between different areas and also maintains a Level 1 Link State Database?

Accepted Answer

L1/L2 router. L1/L2 routers perform both intra-area and inter-area routing, maintaining both L1 and L2 LSDBs.

Answer

Level 2 router

Answer

Level 1 router

Answer

Area Border Router (ABR)

Question 13

An SR-TE policy is configured with a candidate path containing multiple segment lists. Which selection criteria is used to choose the active segment list among the candidate paths?

Accepted Answer

Preference value. The preference value (or priority) is used to select the best candidate path; higher preference wins.

Answer

Color

Answer

Metric type (IGP or TE)

Answer

Hop count

Question 14

A service provider is deploying IPv6 transition mechanisms. Which three technologies use encapsulation over an IPv4 network? (Choose three.)

Accepted Answer

6VPE. 6PE, 6VPE, and 6rd encapsulate IPv6 packets over IPv4; MAP-T uses translation, not encapsulation.

Answer

NAT64

Answer

MAP-T

Question 15

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 uses IPsec for authentication and does not include authentication fields in the OSPF header. It runs per-link instead of per-subnet.

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.