350-501 Practice Test 3 — 10 Questions

Question 1

A service provider is deploying a new MPLS core with Segment Routing and requires fast convergence upon link failure. They plan to use TI-LFA (Topology Independent Loop-Free Alternate). What is a prerequisite for TI-LFA to provide protection against any single link failure?

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

Accepted Answer

IGP must be a link-state protocol with complete topology information (OSPF or IS-IS).. TI-LFA relies on the IGP having a complete view of the network topology to compute a post-convergence path that avoids the failed link. OSPF and IS-IS are link-state protocols that flood link-state advertisements (LSAs) or link-state packets (LSPs) to provide this full topology database, which is essential for TI-LFA to calculate a loop-free backup path for any single link failure.

Answer

BGP-LU must be enabled for label distribution.

Answer

LDP must be enabled on all interfaces.

Answer

RSVP-TE must be configured with FRR.

Question 2

What is the role of Network Services Orchestrator (NSO) in service provider automation?

Accepted Answer

To orchestrate service provisioning across multiple devices. NSO provides service lifecycle management by modeling services with YANG and configuring devices via NETCONF.

Answer

To encrypt data plane traffic

Answer

To provide real-time traffic monitoring

Answer

To replace the routing protocol decision process

Question 3

In a carrier network using VRF-lite for customer isolation, which issue arises if route-target values are not correctly configured?

Accepted Answer

Customer routes leak into other VRFs.. In VRF-lite, route-target (RT) values control the import and export of routes between VRFs. If RTs are misconfigured, a VRF may import routes intended for another VRF, causing customer routes to leak across VRFs. This violates isolation because the VRF table incorrectly accepts routes based on mismatched RT import statements.

Answer

Customer routes are not installed in the global table.

Answer

BGP sessions between PEs flap.

Answer

The PE-CE routing protocol fails.

Question 4

Which TWO statements correctly describe the DiffServ model? (Choose two.)

Accepted Answer

DSCP uses 6 bits, providing 64 possible values. The DiffServ model uses the 6-bit Differentiated Services Code Point (DSCP) field in the IP header to mark packets, providing 2^6 = 64 possible values (0-63). This allows for up to 64 distinct per-hop behaviors (PHBs), enabling scalable QoS classification beyond the limited 8 classes of the older IP Precedence model.

Answer

AF classes use DSCP values 0-7

Answer

Best Effort is marked with DSCP 46

Answer

DiffServ uses a 3-bit field for QoS marking

Question 5

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 unique identifier for a multihomed segment. It is used for DF election, aliasing, and split-horizon.

Answer

Ethernet Tag ID

Answer

Route Distinguisher (RD)

Answer

MPLS Label

Question 6

An SP detects a volumetric DDoS attack targeting a customer network. The SP uses Cisco's S/RTBH technique to drop attack traffic. Which action is performed by the edge routers upon receiving a BGP route with a specific community?

Accepted Answer

The edge router installs a /32 route pointing to a discard interface. S/RTBH works by advertising a /32 prefix (the victim's IP) with a special BGP community (e.g., NO_EXPORT) and a next-hop of the discard interface (e.g., Null0). Edge routers install the route pointing to Null0, dropping traffic to that IP.

Answer

The edge router applies a BGP FlowSpec rule to rate-limit the traffic

Answer

The edge router forwards the attack traffic to a scrubbing center

Answer

The edge router sends ICMP unreachable messages to the attacker

Question 7

In an MPLS-based service provider core network, the aggregation layer typically connects to the core backbone. Which technology is primarily used at the aggregation layer to scale Ethernet services for many customers while preserving VLAN separation?

Accepted Answer

Q-in-Q (IEEE 802.1ad). Q-in-Q (802.1ad) allows service providers to stack a customer VLAN tag on top of a service VLAN tag, enabling scalable customer separation in metro Ethernet networks.

Answer

IEEE 802.1ah (MAC-in-MAC)

Answer

IEEE 802.3ad (Link Aggregation)

Answer

IEEE 802.1x (Port-based Network Access Control)

Question 8

Which Cisco automation tool uses service models in YANG and communicates via NETCONF to orchestrate device configurations and lifecycle management?

Accepted Answer

Cisco Network Services Orchestrator (NSO). NSO (Network Services Orchestrator) uses YANG models and NETCONF for configuration management. Ansible, Cisco DNA Center, and Chef are other tools but NSO is specifically for service orchestration.

Answer

Ansible

Answer

Chef

Answer

Cisco DNA Center

Question 9

An engineer is configuring MPLS VPN and needs to ensure that customer traffic is automatically marked with a specific QoS policy based on the VPN. Which method should be used to propagate QoS markings across the MPLS network?

Accepted Answer

Use MPLS EXP bits to mark traffic at the ingress PE and map to QoS at egress. In an MPLS VPN environment, QoS markings must be preserved across the MPLS backbone. MPLS EXP (Experimental) bits are the standard mechanism to carry QoS information within the MPLS label stack. At the ingress PE, customer traffic is classified and marked with the appropriate EXP bits based on the VPN or other criteria. The egress PE then uses these EXP bits to map traffic to the correct QoS policy, ensuring end-to-end QoS treatment.

Answer

Use 802.1p CoS on the CE-PE link and preserve it across the MPLS backbone

Answer

Use IP ToS bits to mark traffic and rely on MPLS to preserve them

Answer

Set DSCP at the ingress PE and preserve it across the MPLS backbone

Question 10

In IS-IS, which type of LSP is used to advertise prefix information for IPv4 and IPv6 in a modern SP network that supports traffic engineering?

Accepted Answer

TLV 135 (Extended IP Reachability). TLV 135 for IPv4 (extended IP reachability) and TLV 236 for IPv6 (IPv6 reachability) are used in IS-IS for prefix advertisement.

Answer

TLV 2 (IS Neighbors)

Answer

TLV 1 (Area Addresses)

Answer

TLV 22 (IS Extended Neighbors)