350-501 Practice Test 28 — 15 Questions

Question 1

An SP is deploying a Network Services Orchestrator (NSO) for service automation. Which THREE components are integral to NSO architecture? (Select three.)

Accepted Answer

Configuration Database (CDB) for storing state. NSO uses a Configuration Database (CDB) for storing device configurations, YANG models for service definitions, and NEDs (Network Element Drivers) for device abstraction.

Answer

SNMP trap receiver for event monitoring

Answer

Path Computation Element (PCE) for TE

Question 2

During a multicast deployment, some receivers are not receiving the stream. The PIM neighbor table shows the upstream interface is correct. Which command would verify whether the multicast routing table has the correct outgoing interface list?

Accepted Answer

show ip mroute. The 'show ip mroute' command displays the multicast routing table, including the outgoing interface list (OIL) for each multicast group. Since the PIM neighbor table confirms the upstream interface is correct, the issue likely lies in the OIL, which 'show ip mroute' directly verifies. This command shows which interfaces are forwarding multicast traffic and whether they are pruned or in a forwarding state.

Answer

show ip igmp groups

Answer

show ip pim neighbor

Answer

show ip route

Question 3

A service provider is using LISP to provide host mobility. Which LISP component is responsible for storing the mapping of EID to RLOC?

Accepted Answer

Map-Server. In LISP (RFC 6830), the Map-Server (MS) is the central repository that stores the mapping of Endpoint Identifiers (EIDs) to Routing Locators (RLOCs). When an Ingress Tunnel Router (ITR) needs to forward traffic to a destination EID, it queries the Map-Resolver, which in turn contacts the Map-Server to retrieve the authoritative mapping. The Map-Server also accepts registration from Egress Tunnel Routers (ETRs) on behalf of their EID prefixes, making it the definitive source for EID-to-RLOC bindings.

Answer

Altitude

Answer

Tunnel Router

Answer

Map-Resolver

Question 4

A service provider is designing a core network with IS-IS as the IGP. To support MPLS traffic engineering, which IS-IS extensions are required?

Accepted Answer

IS-IS TE extensions (RFC 5305). IS-IS TE extensions (RFC 5305) are required to carry MPLS Traffic Engineering information, such as link bandwidth, administrative groups, and TE metric, in Type-Length-Value (TLV) fields within IS-IS Link State PDUs. These extensions enable the IGP to flood TE attributes that MPLS TE uses for constraint-based path computation, such as with RSVP-TE or Segment Routing.

Answer

IS-IS multi-topology (MT)

Answer

IS-IS wide metrics

Answer

IS-IS L1/L2 routing

Question 5

An SP network uses RSVP-TE for MPLS traffic engineering with FRR link protection. Which THREE statements are correct about RSVP-TE operation and FRR? (Choose three.)

Accepted Answer

In FRR link protection, the 1:1 detour method creates a separate backup LSP for each protected LSP, while the bypass tunnel method protects multiple LSPs over a single backup tunnel.. RSVP-TE uses PATH messages traveling downstream from headend to tailend and RESV messages traveling upstream from tailend to headend, establishing reservation state (D correct). The Explicit Route Object (ERO) in the PATH message specifies the strict or loose hops the traffic must traverse (E correct). For FRR link protection, the 1:1 detour method creates a separate backup LSP for each protected LSP, while the bypass tunnel method protects multiple LSPs over a single backup tunnel (B correct). Option A is incorrect because CSPF computes paths based on both IGP metrics and TE constraints (e.g., bandwidth, affinity), not only IGP metrics. Option C is incorrect because the 'fixed-filter' (FF) style is for per-sender reservation in RSVP, but MPLS-TE typically uses the 'shared-explicit' (SE) style to allow multiple senders (LSPs) to share the same reservation.

Answer

CSPF (Constrained Shortest Path First) is used to compute the best path based on IGP metrics only, ignoring TE constraints.

Answer

The RSVP 'fixed-filter' (FF) reservation style is the only style used in MPLS-TE to allow multiple senders.

Question 6

Which BGP attribute influences inbound traffic to an AS by affecting the path selection of eBGP peers?

Accepted Answer

MED. MED (Multi-Exit Discriminator) is used to influence inbound traffic by suggesting to a neighbor AS which path to use.

Answer

LOCAL_PREF

Answer

Weight

Answer

AS_PATH

Question 7

Which THREE of the following are valid IS-IS TLV types used to support traffic engineering and segment routing? (Choose three.)

Accepted Answer

TLV 22 (Extended IS Reachability). IS-IS TE extensions use various TLVs. TLV 22 (Extended IS Reachability) carries wide metrics and TE information. TLV 135 (Extended IP Reachability) carries IP prefixes with wide metrics. TLV 36 (Prefix SID) is used for segment routing to assign SIDs to prefixes.

Answer

TLV 2 (IS Neighbors)

Answer

TLV 128 (IP Internal Reachability)

Question 8

An SP network is using IS-IS and wants to achieve fast convergence using BFD. Which two statements about BFD in IS-IS are correct?

Accepted Answer

BFD can provide sub-second failure detection for IS-IS adjacencies.. BFD provides fast failure detection (sub-second) and is configured under the interface. IS-IS does not require BFD for normal operation; it's an enhancement.

Answer

BFD requires IS-IS to be configured with wide metrics.

Answer

IS-IS BFD configuration is done under the IS-IS router process.

Answer

BFD replaces the need for IS-IS hello packets.

Question 9

A service provider is deploying MPLS L3VPN to connect multiple customer sites. The PE router receives a route from a CE router via MP-BGP. Which attribute must the PE router add to the route before advertising it to the route reflector?

Accepted Answer

Route distinguisher (RD). When a PE router receives a customer route from a CE router via MP-BGP, it must first make the route unique within the MPLS VPN context by adding a Route Distinguisher (RD). The RD prepended to the IPv4 prefix creates a VPNv4 address (per RFC 4364), which is the format required for advertisement to a route reflector. Without the RD, the route would not be distinguishable from other customers' overlapping IP prefixes in the BGP table.

Answer

MPLS label

Answer

Route target (RT)

Answer

IGP metric

Question 10

An SP is deploying IS-IS fast convergence. Which mechanism triggers an immediate SPF computation when a neighbor fails?

Accepted Answer

BFD (Bidirectional Forwarding Detection). BFD (Bidirectional Forwarding Detection) provides sub-second failure detection and triggers SPF/PRC.

Answer

Partial Route Computation (PRC)

Answer

Event-driven SPF

Answer

IS-IS Hello multiplier

Question 11

A service provider wants to offer a point-to-point Ethernet service between two customer sites with a defined bandwidth and performance guarantee, according to MEF standards. Which Carrier Ethernet service type is appropriate?

Accepted Answer

E-Line. E-Line (Ethernet Line) is a point-to-point service defined by MEF for Carrier Ethernet.

Answer

E-LAN

Answer

E-Access

Answer

E-Tree

Question 12

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) drops packets probabilistically based on queue depth and IP precedence/DSCP, avoiding synchronization and providing congestion avoidance.

Answer

Policing

Answer

LLQ

Answer

CBWFQ

Question 13

An engineer is designing an MPLS network and needs to ensure that VPN traffic between two PE routers is label-switched. The PE routers are connected via a P router and have a full mesh of iBGP sessions. Which label distribution method is required for the VPN labels?

Accepted Answer

MP-BGP. In MPLS VPN architectures, VPN labels (also known as service labels) are distributed using Multiprotocol BGP (MP-BGP). MP-BGP carries VPN-IPv4 routes that include both the route distinguisher (RD) and the VPN label in the Network Layer Reachability Information (NLRI). This allows PE routers to exchange per-VRF label bindings, enabling label-switched VPN traffic across the MPLS core. Without MP-BGP, the PE routers cannot signal the VPN-specific labels required for end-to-end label switching.

Answer

Segment Routing

Answer

RSVP-TE

Answer

LDP

Question 14

A router is receiving a BGP prefix with community 100:100. The operator wants to modify the local preference to 200 for this prefix. Which configuration will achieve this?

Accepted Answer

route-map SET_LP permit 10, match community 100, set local-preference 200. The route-map uses `match community 100` to identify the BGP community value 100:100 (in Cisco's default format, the community is matched without the colon), and `set local-preference 200` modifies the local preference for that prefix to 200. This is the standard method to influence inbound BGP path selection by adjusting local preference based on community matching.

Answer

route-map SET_LP permit 10, match ip address prefix-list, set weight 200

Answer

ip bgp-community new-format, route-map SET_LP permit 10, match community 100, set community 200

Answer

route-map SET_LP permit 10, match community 100, set metric 200

Question 15

In an IS-IS segment routing network, after the global 'segment-routing mpls' configuration, which IS-IS configuration is mandatory for label allocation?

Accepted Answer

segment-routing mpls under router isis. The global 'segment-routing mpls' command enables MPLS Segment Routing on the device, but it does not automatically enable label allocation under IS-IS. The mandatory IS-IS configuration to trigger label allocation is 'segment-routing mpls' under the 'router isis' process. Without this sub-mode command, IS-IS will not allocate MPLS labels for prefixes, even if prefix-SIDs are configured on interfaces.

Answer

mpls label protocol sr

Answer

prefix-sid under the loopback interface

Answer

is-type level-1-2