350-501 Multiple Select — 60 Questions

Question 1

Which TWO are benefits of using Segment Routing (SR) over traditional LDP-based MPLS?

Accepted Answer

Eliminates the need for LDP and RSVP-TE protocols.. Segment Routing (SR) eliminates the need for the Label Distribution Protocol (LDP) and Resource Reservation Protocol with Traffic Engineering (RSVP-TE) by encoding MPLS labels directly into the Interior Gateway Protocol (IGP), such as OSPF or IS-IS. This simplifies the control plane by removing these protocols entirely, reducing operational complexity and resource overhead.

Answer

Requires only OSPF as the IGP.

Answer

Reduces label imposition at the ingress PE.

Answer

Faster convergence due to BGP PIC.

Question 2

Which TWO statements about model-driven telemetry compared to SNMP are correct? (Choose two.)

Accepted Answer

Model-driven telemetry can stream data at sub-second intervals.. Model-driven telemetry (MDT) uses a push model where the network device streams structured data (e.g., YANG-modeled) to a collector, enabling sub-second intervals for real-time monitoring. This contrasts with SNMP's pull model, where the manager polls the device at intervals limited by CPU and network overhead, making sub-second polling impractical.

Answer

Model-driven telemetry uses UDP for transport by default.

Answer

Model-driven telemetry only sends data on change (event-driven).

Answer

Model-driven telemetry uses MIBs to define data structures.

Question 3

Which THREE of the following are required for successful operation of OSPFv3 in an IPv6 service provider network?

Accepted Answer

Interface activation with 'ipv6 ospf area '. OSPFv3 requires interface-level activation using the 'ipv6 ospf area ' command to enable the OSPFv3 process on a specific interface and associate it with an area. Without this, the interface will not participate in OSPFv3 neighbor discovery or routing updates, even if the process is configured globally.

Answer

OSPFv3 authentication configured

Answer

OSPFv3 LSA type 9 for link-local addresses

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 SP network is running OSPFv3 for IPv6 and needs to support traffic engineering extensions for RSVP-TE. Which three statements about OSPFv3 TE extensions are true?

Accepted Answer

OSPFv3 TE uses TLV 1 (Router Address) in Opaque LSAs.. OSPFv3 uses Opaque LSA types 9, 10, and 11 for TE, with Type 10 carrying TE information link-state. OSPFv3 TE requires the OSPFv3 process to be configured for TE.

Answer

OSPFv3 TE requires the use of wide metrics.

Answer

OSPFv3 TE only supports point-to-point links.

Question 6

Which TWO are characteristics of Segment Routing?

Accepted Answer

Source routing capability. Segment Routing (SR) is a source-routing paradigm where the ingress node encodes a list of segments (instructions) into the packet header, guiding the packet through the network without intermediate routers needing to maintain per-flow state. Option B is correct because SR inherently provides source routing capability: the source node determines the path by stacking segment identifiers (SIDs), and transit nodes simply forward based on the top SID.

Answer

Uses only IPv6 data plane

Answer

Requires RSVP-like signaling for path setup

Answer

Requires a centralized SDN controller

Question 7

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.. MPLS-TE uses explicit paths (either strict or loose) to direct traffic away from the shortest path determined by the IGP (e.g., OSPF or IS-IS). This allows network operators to engineer traffic flows based on administrative policies, such as load balancing or avoiding congested links, rather than relying solely on the IGP's metric-based shortest path.

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 8

Which THREE of the following L3VPN services require the use of a dedicated control plane per VPN instance?

Accepted Answer

6VPE. 6VPE (IPv6 VPN Provider Edge) requires a dedicated control plane per VPN instance because it uses separate per-VPN routing tables and a distinct BGP session (typically MP-BGP with the IPv6 address family) to exchange IPv6 VPN routes. This ensures that each customer's IPv6 routing information is isolated and processed independently, which is a core requirement for L3VPN services that maintain per-VPN forwarding and control plane separation.

Answer

VPLS

Answer

MDT VPN

Question 9

A network engineer is configuring management plane security on IOS XR. Which TWO of the following are recommended practices? (Choose two.)

Accepted Answer

Use SNMPv3 with authentication and encryption. SSH provides encrypted remote access, and SNMPv3 with encryption and authentication secures monitoring. Telnet and SNMPv2c are insecure. Disabling all access is not practical.

Answer

Use SNMPv2c with read-only community strings

Answer

Disable all remote access and use console only

Answer

Enable Telnet for remote access

Question 10

An SP engineer is implementing DSCP classification at the edge. Which two AF classes are typically used for mission-critical data? (Choose two.)

Accepted Answer

AF41. AF4x (e.g., AF41/AF42/AF43) and AF3x (e.g., AF31/AF32/AF33) are used for high-priority data. AF1x is low-priority.

Answer

CS0

Answer

AF11

Answer

AF22

Question 11

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 12

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 13

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 14

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 15

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 16

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 17

An SP is migrating its core network to Segment Routing (SR-MPLS). The network uses IS-IS as the IGP with SR extensions. Which three statements about SR-MPLS architecture are correct?

Accepted Answer

Adjacency SIDs are local to a router and indicate a specific link.. An Adjacency SID is a local label assigned to a specific IS-IS adjacency, representing a particular link between two routers. It is locally significant and used to steer traffic over that specific next-hop, not globally unique.

Answer

The OSPF protocol cannot be used for SR-MPLS because it does not support SR extensions.

Answer

The SRGB must be identical across all routers in the domain to ensure global uniqueness.

Question 18

Which two statements correctly describe the use of DSCP values in the DiffServ model? (Choose two.)

Accepted Answer

DSCP is a 6-bit field allowing 64 distinct values.. DSCP is a 6-bit field with 64 possible values. Per-hop behaviors (PHBs) like EF and AF are defined by DSCP values.

Answer

DSCP values are mapped to MPLS EXP bits at the egress PE.

Answer

DSCP values are used only for voice traffic.

Answer

DSCP value 0 indicates low latency traffic.

Question 19

An engineer is troubleshooting an MPLS network where some routers are not exchanging labels via LDP. Which two steps are most appropriate for diagnosing the issue? (Choose two.)

Accepted Answer

Verify LDP neighbor adjacencies using 'show mpls ldp neighbor'.. Verifying LDP sessions with 'show mpls ldp neighbor' and checking interfaces with 'show mpls ldp interface' are standard first steps. Checking MTU or OSPF neighbors are less direct.

Answer

Check the MTU size on all interfaces.

Answer

Reboot all routers to reset LDP sessions.

Answer

Verify that OSPF neighbor relationships are established.

Question 20

Which two actions are performed by an MPLS label edge router (LER) when it receives an unlabeled IP packet destined for a prefix with an LSP? (Choose two.)

Accepted Answer

It forwards the packet based on the MPLS label.. The LER (or ingress LSR) imposes a label stack (push operation) on the packet, then forwards it based on the label. It does not swap labels (that's done by LSRs), nor does it pop the label (egress LER does).

Answer

It performs a recursive lookup in the LFIB.

Answer

It performs a label swap operation.

Answer

It pops the top label and forwards based on the inner header.