350-501 Practice Test 39 — 15 Questions

Question 1

Which TWO statements correctly describe differences between PIM dense mode and PIM sparse mode? (Choose two.)

Accepted Answer

PIM-DM assumes all downstream routers want to receive multicast traffic, so it initially floods traffic.. Option D is correct because PIM-DM (dense mode) operates on a flood-and-prune model: it assumes every downstream router wants the multicast stream, so it initially floods traffic across the source tree and then prunes branches that send explicit Prune messages. Option E is correct because PIM-SM (sparse mode) is built around a shared tree rooted at a Rendezvous Point (RP), which receivers join via explicit (*,G) Join messages so that traffic is only delivered where it is requested. Option A is wrong because BSR is a PIM-SM mechanism for dynamically discovering RPs, not a PIM-DM feature. Option B is wrong because sparse mode is more bandwidth efficient for low-density groups (receivers sparsely distributed), whereas dense mode suits high-density groups. Option C is wrong because it reverses the models: PIM-SM uses explicit joins, while PIM-DM uses flood and prune.

Answer

PIM-DM supports the use of a bootstrap router (BSR) for RP discovery.

Answer

PIM-SM is more bandwidth efficient for high density groups.

Answer

PIM-DM uses explicit join messages, while PIM-SM uses flood and prune.

Question 2

Which TWO are essential components for deploying EVPN in a service provider network?

Accepted Answer

Overlay tunnel encapsulation such as VXLAN or MPLS. Option A is correct because EVPN is an overlay control-plane technology that requires a data-plane encapsulation to carry tenant MAC/IP reachability across the provider backbone, typically VXLAN in data-center contexts or MPLS (e.g., EVPN-MPLS with BGP MPLS-based Ethernet VPN per RFC 7432) in service provider networks. Option C is correct because EVPN uses BGP as its control plane, specifically MP-BGP with the EVPN address family (AFI 25 / SAFI 70) to advertise MAC/IP Advertisement routes, Inclusive Multicast Ethernet Tag routes, and Ethernet Auto-Discovery routes, enabling MAC learning and multihoming. OSPF (Option B) is not essential because the underlay can be any IGP (IS-IS, OSPF, or even eBGP) or a static routing design; it is a design choice, not a required EVPN component. PIM-SM (Option D) is not required because EVPN natively handles BUM traffic via ingress replication or assisted replication using the Inclusive Multicast Ethernet Tag route, without needing PIM in the underlay. RSVP-TE (Option E) is not essential because EVPN does not mandate traffic-engineered LSPs; it only needs transport reachability between PE routers, which can be provided by plain IGP-based forwarding or SR/SR-MPLS.

Answer

OSPF as the underlay routing protocol

Answer

PIM-SM for multicast replication

Answer

RSVP-TE for path computation

Question 3

A network automation engineer needs to retrieve QoS policy statistics from a Cisco IOS XE device using RESTCONF. Which YANG module should be targeted?

Accepted Answer

Cisco-IOS-XE-QoS. The Cisco-IOS-XE-QoS YANG module is the native Cisco module that provides the data model for QoS policy configuration and operational statistics on IOS XE devices. Since the engineer is using RESTCONF to retrieve QoS statistics from a Cisco IOS XE device, this module is the correct target because it is specifically designed for and supported on IOS XE platforms.

Answer

ietf-qos

Answer

Cisco-NX-OS-device

Answer

openconfig-qos

Question 4

Which Cisco SP router platform uses IOS XR and is commonly deployed at the aggregation layer, supporting both L2 and L3 services?

Accepted Answer

Cisco ASR 9000. Cisco ASR 9000 is an aggregation router running IOS XR, suitable for L2/L3 services.

Answer

Cisco CRS

Answer

Cisco ASR 1000

Answer

Cisco NCS 540

Question 5

Which TWO of the following are characteristics of MPLS-TE (Traffic Engineering)?

Accepted Answer

Uses explicit paths to route traffic away from shortest-path IGP.. Option A is correct because MPLS-TE's defining feature is the use of explicitly signaled paths (via RSVP-TE) that can override the IGP's shortest-path forwarding, allowing traffic to be steered onto non-shortest paths to avoid congestion. Option C is correct because MPLS-TE supports resource reservation through RSVP-TE, advertising available bandwidth and reserving it per tunnel, along with setup/holding priorities (and preemption) to control which tunnels get bandwidth first. Option B is incorrect because TE tunnels are signaled with RSVP-TE, not LDP; LDP distributes labels for normal IGP-based LSPs and does not support explicit paths or bandwidth reservation. Option D is incorrect because MPLS TE does not require per-platform label space; per-platform label space is a general MPLS label allocation concept, not a TE-specific requirement, and TE tunnels work with standard label distribution. Option E is incorrect because MPLS-TE tunnels can traverse routers in different OSPF areas (or even different IGPs/domains) as long as the path is reachable and signaled; there is no requirement that all routers in the tunnel share the same OSPF area.

Answer

Uses LDP for label distribution along the TE tunnel.

Answer

Requires per-platform label space for TE tunnels.

Answer

Requires all routers in the TE tunnel to be in the same OSPF area.

Question 6

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?

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 7

An SP router is configured with CBWFQ. For a data class requiring 30% bandwidth guarantee, which command is correct in the policy-map?

Accepted Answer

bandwidth percent 30. The 'bandwidth percent' command allocates a percentage of the interface bandwidth to the class.

Answer

fair-queue

Answer

priority percent 30

Answer

bandwidth 30

Question 8

A network administrator configures a class map to match VoIP traffic using 'match ip dscp ef' on a Cisco router. However, the QoS policy is not applying the expected marking to VoIP packets. What is a possible reason?

Accepted Answer

The VoIP traffic is not marked with DSCP EF from the source.. The 'match ip dscp ef' command in the class map checks the DSCP value already present in the incoming VoIP packets. If the source device (e.g., an IP phone) does not mark the packets with DSCP EF (46), the class map will not match, and the QoS policy will not apply the expected marking. The policy can only re-mark packets that are already matched by the class map.

Answer

The policy is applied in the output direction instead of input.

Answer

The policy is applied to the wrong interface.

Answer

The class map uses the wrong match type.

Question 9

An SP network uses MPLS to provide IPv6 connectivity over an IPv4 backbone using 6PE. Which BGP extension is required on the provider edge routers to exchange IPv6 prefixes with an IPv4 next-hop?

Accepted Answer

BGP multiprotocol extensions (MP-BGP) with IPv6 address family. 6PE uses BGP multiprotocol extensions (MP-BGP) with an AFI of 2 (IPv6) and SAFI of 1 (unicast), and the next-hop is encoded as an IPv4 address using the 'next-hop' attribute.

Answer

BGP route reflection

Answer

BGP confederation

Answer

BGP prefix-independent convergence (PIC)

Question 10

An SP is deploying IS-IS fast convergence using Partial Route Computation (PRC). Under which condition does PRC occur?

Accepted Answer

When a prefix is added or removed without topology change. PRC is triggered when a prefix changes but the topology remains unchanged. It recalculates only the affected prefixes, not the entire SPF tree.

Answer

When the IS-IS metric changes

Answer

When the system ID changes

Answer

When a new adjacency is formed

Question 11

An SP has configured MPLS TE tunnels for traffic engineering. To verify the status of the TE tunnels, which command provides the most relevant information?

Accepted Answer

show mpls traffic-eng tunnels brief. The 'show mpls traffic-eng tunnels brief' command directly displays the status, state (up/down), and key parameters (e.g., bandwidth, path) of all configured MPLS TE tunnels, making it the most relevant command for verifying TE tunnel status. It provides a concise view of tunnel endpoints, admin/operational states, and signaled bandwidth, which is essential for traffic engineering verification.

Answer

show mpls forwarding-table

Answer

show mpls ldp tunnels

Answer

show ip rsvp reservation

Question 12

A large SP plans to deploy SR-TE tunnels across the backbone using an SDN controller for path computation. To ensure fast convergence and scalability, which automation approach should be used for tunnel creation?

Accepted Answer

PCEP with stateful delegation to controller. B is correct because PCEP with stateful delegation allows the SDN controller to compute and instantiate SR-TE tunnels dynamically, while the router delegates control to the controller for path updates. This approach ensures fast convergence by enabling the controller to react to network changes in real time and scales efficiently by centralizing path computation, avoiding per-router configuration overhead.

Answer

Static configuration on each router

Answer

RSVP-TE tunnels

Answer

NetFlow-based path selection

Answer

SNMP traps

Question 13

A service provider is deploying a new MPLS core network. The network has four routers: P1, P2, PE1, and PE2. OSPF is used as the IGP. The engineer configures MPLS LDP on all interfaces. After enabling LDP, the engineer notices that the LDP session between P1 and P2 is established, but no labels are exchanged for the loopback0 interfaces of PE1 and PE2. The loopback0 addresses are advertised in OSPF. The engineer verifies that the OSPF routes are present in the routing table of all routers. What is the most likely reason for the missing labels?

Accepted Answer

An access-list is applied under 'mpls ldp advertise-labels' that denies the loopback prefixes.. The most likely reason is that an access-list is applied under 'mpls ldp advertise-labels' that denies the loopback prefixes. LDP by default advertises labels for all prefixes in the routing table, but the 'advertise-labels' command can filter which prefixes receive labels. If the loopback0 prefixes of PE1 and PE2 are denied by such an access-list, no labels will be advertised for them, even though OSPF routes are present.

Answer

LDP is using UDP for label exchange.

Answer

The OSPF cost to the loopbacks is too high.

Answer

The loopback interfaces are not enabled with 'mpls ip'.

Question 14

Refer to the exhibit. An engineer makes a RESTCONF request to retrieve operational data for all interfaces, but the response shows only one interface. What is the most likely cause?

Accepted Answer

The request path includes a specific interface key, filtering the result. If the RESTCONF request path includes a specific interface key (e.g., /restconf/data/ietf-interfaces:interfaces/interface=GigabitEthernet0/0/0), the API will return only that single interface's operational data, even if the engineer intended to retrieve all interfaces. RESTCONF uses URI-encoded keys to filter resources; omitting the key returns the entire list, while including a key narrows the response to that specific instance.

Answer

The interfaces are in different VRFs

Answer

The device does not support the YANG model

Answer

The engineer used the wrong HTTP method

Answer

The collector is not subscribed to telemetry

Question 15

Which TWO statements correctly describe Segment Routing characteristics? (Select two.)

Accepted Answer

The path is encoded as a label stack at the source router. Option B is correct because Segment Routing encodes the entire forwarding path as an ordered list of segments (SIDs) in a label stack that is imposed by the ingress/source router, so the source dictates the path without per-hop signaling. Option C is correct because SR uses IGP extensions (IS-IS or OSPF) or BGP to advertise SIDs, eliminating the need for LDP or RSVP-TE to distribute labels or set up paths. Option A is wrong because routers can use different SRGB (Segment Routing Global Block) values as long as the SID-to-index mapping is consistent; the SRGB need not be identical across all routers. Option D is wrong because core routers still maintain per-prefix SID state (the SID/label mappings learned via IGP), so SR does not eliminate all per-prefix state. Option E is wrong because traffic engineering policies in SR are typically instantiated via a controller or headend using SID lists, and the SIDs themselves are advertised through IGP extensions (or BGP-LS for topology), not distributed as TE policies via BGP without IGP extensions.

Answer

All routers must be configured with the same SRGB value

Answer

SR eliminates all per-prefix state from core routers

Answer

Traffic engineering policies are distributed via BGP without any IGP extension