350-501 Practice Test 4 — 25 Questions

Question 1

In EVPN multi-homing, which two mechanisms are used to avoid duplicate packets and ensure efficient forwarding? (Choose two.)

Accepted Answer

Split-horizon filtering. Designated Forwarder (DF) election ensures only one PE forwards traffic to the CE for broadcast/multicast/unknown unicast, and split-horizon prevents a PE from forwarding packets back to the ES from which they were received.

Answer

MAC mobility

Answer

Aliasing

Answer

ARP suppression

Question 2

In IS-IS, which TWO are types of Link State PDUs (LSPs)?

Accepted Answer

Level 2 LSP. In IS-IS, Link State PDUs (LSPs) are the fundamental building blocks of the link-state database. They carry topology and prefix information and are generated by each router. There are two distinct types: Level 1 LSPs, which advertise information within the same area, and Level 2 LSPs, which advertise information between areas. Options B and E correctly identify these two types.

Answer

Partial Sequence Numbers PDU (PSNP)

Answer

Hello LSP

Answer

Complete Sequence Numbers PDU (CSNP)

Question 3

Which TWO statements correctly describe the use of OSPF in a service provider network?

Accepted Answer

OSPF uses different LSA types to advertise different types of routing information.. OSPF uses different LSA types (e.g., Type 1 Router LSA, Type 2 Network LSA, Type 3 Summary LSA, Type 5 AS-External LSA) to advertise different categories of routing information, such as router links, network links, inter-area routes, and external routes. This LSA-type differentiation is fundamental to OSPF's link-state architecture, enabling efficient flooding and route computation within and across areas.

Answer

OSPF uses the Bellman-Ford algorithm to compute routes.

Answer

OSPF is a distance-vector routing protocol.

Answer

OSPF uses TLVs to encode routing information.

Question 4

In a carrier-supporting carrier (CSC) architecture, the customer carrier runs MPLS in its network. Which technology is used to exchange VPN routes between the provider carrier and the customer carrier?

Accepted Answer

MP-BGP with VPNv4 address family. In a carrier-supporting-carrier (CSC) architecture, the customer carrier runs MPLS in its network and needs to exchange VPN routes (e.g., customer VPN prefixes) with the provider carrier. MP-BGP with the VPNv4 address family is the correct technology because it carries both the IPv4 prefix and the Route Distinguisher (RD), enabling the provider carrier to distinguish overlapping VPN routes from different customer VPNs. This is defined in RFC 4364 and is the standard inter-AS VPN option for CSC scenarios.

Answer

OSPF

Answer

EIGRP

Answer

IPv4 BGP

Question 5

Which THREE of the following are key components of an MPLS L3VPN architecture? (Choose three.)

Accepted Answer

VRF on PE routers. VRF (Virtual Routing and Forwarding) on PE routers is a key component because it isolates customer routing tables and forwarding planes within the provider edge, allowing multiple customers to share the same physical infrastructure while maintaining separate routing domains. Each VRF maintains its own routing table, CEF (Cisco Express Forwarding) table, and associated interfaces, which is fundamental to L3VPN separation.

Answer

RSVP-TE for traffic engineering

Answer

P routers with full VPN routing tables

Question 6

An engineer is troubleshooting MPLS LSP connectivity. The ingress PE router has the label binding for the FEC 10.1.1.0/24, but no LSP is established. Which command should be checked on the P routers to verify the LSP path?

Accepted Answer

show mpls forwarding-table. The correct command is 'show mpls forwarding-table' because it displays the LFIB (Label Forwarding Information Base) on each P router. Since the ingress PE has a label binding for FEC 10.1.1.0/24 but no LSP is established, the issue likely lies in label propagation or forwarding along the path. Checking the LFIB on P routers reveals whether they have installed the correct outgoing label and interface for that FEC, which is essential for LSP connectivity.

Answer

show mpls interface

Answer

show mpls ldp neighbor

Answer

show ip route 10.1.1.0

Question 7

Which THREE of the following are required components for implementing MPLS Layer 3 VPN (L3VPN) in a service provider network? (Choose three.)

Accepted Answer

MP-BGP between PE routers to exchange VPNv4 routes. MP-BGP (Multiprotocol BGP) is essential for carrying VPNv4 routes between PE routers. It uses address family VPNv4 to transport customer IPv4 prefixes along with their Route Distinguisher (RD) and Route Target (RT) attributes, enabling the separation and distribution of multiple customer VPNs across the MPLS core.

Answer

IBGP between PE and P routers for label distribution

Answer

VRF configuration on P routers

Question 8

A network operator is implementing segment routing (SR-MPLS) using OSPF as the IGP. Which OSPF TLV is used to advertise the Node SID (Prefix SID) for a router's loopback address?

Accepted Answer

Extended Prefix TLV. In OSPF, the Extended Prefix TLV (type 1) carries the Prefix SID sub-TLV for segment routing. The Adjacency SID is carried in the Extended Link TLV.

Answer

Router Information TLV

Answer

Traffic Engineering TLV

Answer

Extended Link TLV

Question 9

Refer to the exhibit. The VRF CUSTOMER is configured with route-target import 100:1. Why is this route not installed in the VRF table?

Accepted Answer

Route target mismatch.. B is correct because the VRF CUSTOMER is configured with route-target import 100:1, but the route in question carries a different route-target value (e.g., 100:2). For a route to be installed into a VRF table, the route-target extended community attached to the route must match at least one of the import route-targets configured on the VRF. A mismatch prevents the route from being imported, even if other conditions are satisfied.

Answer

VRF not properly configured.

Answer

Route distinguisher missing.

Answer

Next-hop unreachable.

Question 10

A service provider wants to mitigate DDoS attacks by blackholing traffic destined to a victim IP address. They plan to use Remotely Triggered Black Hole (RTBH) filtering. What BGP community is commonly used to trigger the blackhole route?

Accepted Answer

Community 666. RTBH works by advertising a /32 route with a specific community (often 666 or a locally defined one) that causes the router to forward traffic to a null interface. The well-known community for RTBH is often 666 or custom.

Answer

Community 100

Answer

Community no-export

Answer

Community local-AS

Question 11

Which LDP mode uses downstream unsolicited label distribution and liberal label retention?

Accepted Answer

Downstream unsolicited with liberal retention. Downstream unsolicited (DU) label distribution is the default mode in LDP, where each LSR advertises labels for all its directly connected prefixes to its neighbors without waiting for a request. Liberal label retention means the LSR stores all received label bindings, even if they are not currently used for forwarding, which enables rapid convergence upon topology changes.

Answer

Downstream on demand with liberal retention

Answer

Upstream unsolicited with liberal retention

Answer

Downstream on demand with conservative retention

Question 12

An engineer wants to configure SR-TE without using RSVP. Which mechanism does SR-TE use to specify the explicit path?

Accepted Answer

Segment list in SR Policy. SR-TE uses a segment list consisting of Node SIDs and/or Adjacency SIDs to define the explicit path, avoiding RSVP state.

Answer

ERO in RSVP PATH message

Answer

Label stack with PHP

Answer

IGP shortest path only

Question 13

Which label operation is performed on a router when an MPLS packet arrives with a top label that matches a local label assigned to a directly connected prefix?

Accepted Answer

Pop. If the top label corresponds to a directly connected prefix, the router will pop the label (penultimate hop popping or explicit null) and forward the packet based on the inner header.

Answer

No operation, label is ignored

Answer

Push

Answer

Swap

Question 14

An engineer is configuring RSVP-TE fast reroute for link protection. Which protection method uses a pre-configured bypass tunnel that protects multiple LSPs on the same link?

Accepted Answer

Facility backup. In RSVP-TE FRR, facility backup uses a bypass tunnel that can protect multiple LSPs on the same link. In contrast, 1:1 detour creates a separate detour LSP for each protected LSP.

Answer

Local Path Protection

Answer

Global Repair

Answer

1:1 detour

Question 15

Which LDP label distribution mode is characterized by a router advertising labels for all prefixes in its routing table to all neighbors, regardless of whether they are needed?

Accepted Answer

Downstream unsolicited with liberal label retention. Downstream unsolicited means the router sends label bindings without being asked; liberal label retention means it keeps all bindings even if not from the next hop.

Answer

Downstream on demand with conservative label retention

Answer

Downstream on demand with liberal label retention

Answer

Downstream unsolicited with conservative label retention

Question 16

In EVPN-VPWS, which identifier is used to uniquely identify an Ethernet Segment for multi-homing?

Accepted Answer

ESI. The Ethernet Segment Identifier (ESI) uniquely identifies an Ethernet segment that is multi-homed to two or more PEs.

Answer

Route Distinguisher

Answer

EVI

Answer

MAC address

Question 17

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 18

Which THREE of the following are standard per-hop behaviors (PHBs) in the DiffServ model? (Select three.)

Accepted Answer

Default (Best Effort). The DiffServ model defines EF (Expedited Forwarding), AF (Assured Forwarding), and Default (BE) PHBs. CS is Class Selector, but not a separate PHB; it is part of AF? Actually CS is a backward-compatible PHB. Standard ones are EF, AF, and Default.

Answer

LLQ

Answer

CS (Class Selector)

Question 19

An SP engineer is configuring hierarchical QoS on a PE router to enforce a per-subscriber bandwidth contract of 10 Mbps and prioritize voice within that contract. Which MQC configuration sequence is correct?

Accepted Answer

Define child class-map and policy-map with LLQ, then parent policy-map with shape and service-policy child, applied to interface.. Hierarchical QoS uses a parent policy for shaping and a child policy for classification and priority queuing. The child is applied to the parent's class-default.

Answer

Define parent policy-map with shape, then child policy-map with LLQ, apply child directly to interface.

Answer

Use policing in the parent policy to enforce 10 Mbps and child for LLQ.

Answer

Define one policy-map with both shape and LLQ in the same class.

Question 20

When using NETCONF to edit a running configuration on a Cisco IOS XR router, which sequence of operations is correct?

Accepted Answer

, on candidate, , . NETCONF uses to modify the config; retrieves; prevents concurrent edits.

Answer

on candidate, then to running

Answer

<edit-config> on running, no lock needed

Answer