350-501 Practice Test 33 — 15 Questions

Question 1

Which TWO are key features of IOS XR architecture? (Choose two.)

Accepted Answer

Distributed OS with process separation. Option C is correct because IOS XR is built as a distributed operating system in which processes are isolated from one another, so a failure in one process (for example, a routing protocol) cannot crash the entire system, and components can run on different line cards or nodes. Option E is correct because IOS XR uses a commit-based configuration model in which changes are staged in a target configuration, validated, and only applied when the administrator issues the commit command, with the ability to roll back to a previous committed configuration. The unmarked options do not belong: A is wrong because IOS XR validates configuration before applying it rather than applying changes immediately without validation; B is wrong because IOS XR is not a monolithic kernel with a shared memory address space but rather a modular, memory-protected, distributed architecture; and D is wrong because IOS XR does not run all routing protocols in a single process but instead separates them into individual, independently restartable processes.

Answer

Configuration applied immediately without validation

Answer

Monolithic kernel with shared memory address space

Answer

Single process for all routing protocols

Question 2

Which technology allows a service provider to offer different classes of service over a single MPLS network?

Accepted Answer

QoS. QoS (Quality of Service) enables a service provider to differentiate traffic by marking packets with specific DSCP or IP precedence values and applying policies such as policing, shaping, and queuing. This allows multiple classes of service (e.g., voice, video, best-effort) to be carried over a single MPLS network while guaranteeing bandwidth, latency, and jitter requirements for each class.

Answer

BGP

Answer

LDP

Answer

MPLS VPN (VRF)

Question 3

Which TWO statements about EVPN Route Type 2 (MAC/IP advertisement) are correct?

Accepted Answer

It is used for MAC learning and ARP suppression. Option A is correct because EVPN Route Type 2 (MAC/IP Advertisement) is the route type that carries host MAC addresses (and optionally IP addresses) across the BGP EVPN control plane, enabling remote MAC learning and, when the IP is included, ARP/ND suppression on the ingress PE. Option B is correct because the Type 2 NLRI explicitly encodes both the MAC address and, optionally, the IP address of a host, which is why it is called MAC/IP Advertisement. Option C is incorrect because load balancing via aliasing is a function of Route Type 1 (Ethernet Auto-Discovery) with the aliasing flag, not Type 2. Option D is incorrect because the Ethernet Segment Identifier is carried in Route Type 1 (and Type 4), not in the Type 2 MAC/IP Advertisement route. Option E is incorrect because Type 2 is precisely the route type used to signal host mobility, with MAC Mobility extended community enabling moves between PEs.

Answer

It provides load balancing via aliasing

Answer

It includes the Ethernet Segment Identifier (ESI)

Answer

It is not used for host mobility

Question 4

An SP network uses OSPFv3 for IPv6 routing. Which three statements about OSPFv3 are true? (Choose three.)

Accepted Answer

OSPFv3 uses link-local addresses for next-hop. Option B is correct because OSPFv3 uses IPv6 link-local addresses (fe80::/10) as the source for hello packets and as the next-hop for routes learned over a link, which is why adjacencies can form without any global IPv6 addressing. Option C is correct because OSPFv3 retains the same fundamental LSA types as OSPFv2 (Router, Network, Inter-Area Prefix, AS External, etc.) but redefines their formats to be IPv6-centric and address-family independent, removing IPv4-specific fields. Option E is correct because OSPFv3 supports multiple instances per link via the Instance ID field in the packet header, allowing separate OSPFv3 processes to run independently on the same interface. Option A is not correct because OSPFv3 runs directly over IPv6 and does not require an IPv4 address on the interface to form adjacencies. Option D is not correct because OSPFv3 relies on the IPv6 Authentication Header and Encapsulating Security Payload (IPsec AH/ESP) as defined in RFC 4552, but authentication is not mandatory and IPsec is not the only or default mechanism; the statement as written is not a universally true characteristic.

Answer

OSPFv3 requires an IPv4 address on the interface to form adjacencies

Answer

OSPFv3 uses IPsec for authentication

Question 5

An SP engineer is designing a QoS policy for a business customer with three traffic classes: Voice (critical latency), Transactional Data (low delay), and Bulk Data (no strict requirements). The link is 100 Mbps. Which TWO actions should be part of the policy? (Select two.)

Accepted Answer

Apply LLQ to the voice class with a policer to limit its rate to 10 Mbps.. Option B is correct because Low Latency Queuing (LLQ) gives the voice class strict priority scheduling, which minimizes latency and jitter for real-time traffic, and the 10 Mbps policer caps the priority queue so it cannot starve the other classes on the 100 Mbps link. Option E is correct because CBWFQ on the transactional data class guarantees a 30 Mbps bandwidth allocation, providing the low-delay, assured treatment that transactional traffic needs without requiring strict priority. Option A is not appropriate because FIFO offers no differentiated treatment and would not isolate bulk traffic from delay-sensitive classes. Option C is wrong because WRED is a congestion-avoidance drop mechanism unsuited to voice, which should be protected by priority queuing rather than early drops. Option D is wrong because a uniform 1000-packet queue limit ignores the differing latency and buffering needs of the three classes.

Answer

Use FIFO queuing for the bulk data class.

Answer

Use WRED on the voice class for congestion avoidance.

Answer

Set the queue limit to 1000 packets for all classes.

Question 6

A service provider is deploying a QoS policy for a customer with voice, mission-critical data, and best-effort traffic. The voice requires strict priority and low latency. Which queuing mechanism should be used to ensure voice packets are always served before other queues, and what additional measure is necessary to prevent voice traffic from starving other traffic?

Accepted Answer

LLQ for voice; policing on the priority queue to limit voice traffic to a configured rate.. LLQ (Low Latency Queuing) provides strict priority queuing for voice traffic, ensuring it is served before other queues. To prevent voice from starving other traffic, policing on the priority queue is necessary to limit voice traffic to a configured rate. CBWFQ does not provide strict priority, FIFO does not prioritize, and WRED is a congestion avoidance mechanism, not a queuing mechanism for strict priority.

Answer

FIFO queuing with a priority list; no policing needed because FIFO handles voice adequately.

Answer

CBWFQ with bandwidth percent for voice; no additional measure needed because CBWFQ inherently prevents starvation.

Answer

WRED for voice; tail drop for data; this ensures low latency for voice.

Question 7

A service provider is implementing BGP security measures to prevent route hijacking. Which TWO mechanisms directly validate the origin AS of BGP prefixes? (Choose two.)

Accepted Answer

RPKI Origin Validation using ROAs. RPKI Origin Validation uses ROAs to verify that the origin AS is authorized to advertise a prefix. BGPSec cryptographically validates the entire AS path, including the origin AS. Both directly validate the origin AS. Prefix lists and route-maps filter based on attributes but do not validate origin. Community filtering manipulates communities but does not validate origin.

Answer

BGP prefix lists

Answer

BGP route-maps with AS path matching

Answer

BGP community-based filtering

Question 8

When configuring an MPLS-TE tunnel with affinity/constraint-based routing, what is the effect of assigning a link attribute of 'red' and setting the tunnel's affinity to include 'red' with the 'include-all' keyword?

Accepted Answer

The tunnel must use only links that have the 'red' attribute.. In MPLS-TE affinity/constraint-based routing, the 'include-all' keyword means the tunnel's affinity bits must all be present on a link for that link to be usable. Assigning the link attribute 'red' and setting the tunnel affinity to include 'red' with 'include-all' therefore forces the tunnel to use only links that carry the 'red' attribute. Links without 'red' are excluded from path computation.

Answer

The tunnel will prefer links with 'red' but may use others if necessary.

Answer

The tunnel will use a strict explicit path.

Answer

The tunnel will avoid links with 'red'.

Question 9

An SP is deploying Deep Packet Inspection (DPI) to classify traffic for QoS and security. Which DPI technique is used to identify applications regardless of port numbers?

Accepted Answer

Signature-based pattern matching. DPI inspects packet payloads using signatures, pattern matching, or behavioral analysis to identify applications, even if they use non-standard ports.

Answer

IP address filtering

Answer

Port-based classification

Answer

NetFlow analysis

Question 10

An engineer is configuring MPLS LDP on a Cisco router. Which TWO statements about LDP operation are correct? (Choose two.)

Accepted Answer

LDP discovers neighbors using UDP hello messages on port 646, and then establishes a TCP session on port 646.. Option B is correct because LDP uses UDP hello messages sent to port 646 for neighbor discovery on the local subnet, and once a neighbor is found it establishes a TCP session (also on port 646) to exchange label bindings reliably. Option D is correct because in liberal label retention mode a router keeps all label bindings received from LDP peers, including those from neighbors that are not the next hop for the FEC, which allows a backup path to be used immediately if the topology changes and thus speeds convergence. Option A is incorrect because the LFIB stores both incoming and outgoing label mappings (and associated next-hop/interface information) for forwarding labeled packets, not just the outgoing label mapping. Option C is incorrect because LDP by default uses downstream unsolicited label distribution, advertising labels without waiting for a request, not downstream-on-demand. Option E is incorrect because LDP can allocate and advertise labels independently of IGP convergence timing, and it does not automatically allocate labels for all IGP routes by default.

Answer

The LFIB (Label Forwarding Information Base) in LDP is used to store only the outgoing label mapping for each FEC.

Answer

LDP uses a downstream-on-demand label distribution method, where labels are sent only when requested by an upstream router.

Answer

LDP label allocation happens only after the IGP converges, and labels are allocated for all IGP routes by default.

Question 11

Which label distribution protocol is replaced by segment routing in SR-MPLS deployments?

Accepted Answer

LDP. In SR-MPLS deployments, segment routing replaces LDP as the label distribution protocol. LDP traditionally distributes labels for each prefix in the IGP, while segment routing uses the IGP itself to advertise prefix-SIDs and adjacency-SIDs, eliminating the need for a separate label distribution protocol. This simplifies the control plane and removes the dependency on LDP.

Answer

RSVP-TE

Answer

IGP itself

Answer

BGP

Question 12

Which two of the following are characteristics of MPLS Traffic Engineering that differentiate it from pure MPLS forwarding?

Accepted Answer

Allows bandwidth reservation. MPLS Traffic Engineering (MPLS-TE) explicitly supports bandwidth reservation, which allows an operator to guarantee a certain amount of bandwidth for a traffic-engineered LSP. This is a key differentiator from pure MPLS forwarding, where LSPs are created without any bandwidth awareness and simply forward packets based on the label-swapping mechanism.

Answer

Requires LDP for LSP creation

Answer

Provides optimal load balancing based on topology

Answer

Uses RSVP for label distribution

Question 13

In an MPLS network, which field in the MPLS label header is used to carry QoS information between LSRs?

Accepted Answer

EXP bits. In MPLS, the EXP (Experimental) bits, also known as the Traffic Class (TC) field per RFC 5462, are 3 bits in the MPLS label header used to carry Quality of Service (QoS) information between Label Switch Routers (LSRs). These bits allow LSRs to apply per-hop behaviors (PHBs) such as queuing and scheduling based on the packet's QoS class, enabling differentiated services across the MPLS network.

Answer

ToS

Answer

IP Precedence

Answer

DSCP

Question 14

A service provider is designing a QoS policy for a multi-service MPLS VPN network that carries voice, video, and data traffic. The network uses DiffServ and MPLS EXP markings. The design must ensure that voice traffic is given priority over video and data, while video traffic should have better treatment than data but not at the expense of voice. The provider plans to use a hierarchical QoS (HQoS) policy at the PE-CE interfaces. Which configuration approach best meets these requirements?

Accepted Answer

Apply a parent policy with a shape for the total bandwidth and a child policy with LLQ for voice and CBWFQ for video and data.. Hierarchical QoS (HQoS) allows the service provider to enforce a total bandwidth shape at the parent level while using a child policy to apply LLQ for voice (ensuring strict priority) and CBWFQ for video and data (ensuring video gets better treatment than data without starving voice). This meets the requirement that video should not degrade voice, as the parent shape prevents any single class from monopolizing the link, and the child policy’s LLQ guarantees voice priority over all other traffic.

Answer

Mark voice traffic with EXP 5, video with EXP 4, and data with EXP 0, and rely on the core to prioritize based on EXP.

Answer

Use a single-level policy with LLQ for voice and video together, and CBWFQ for data.

Answer

Apply class-based shaping to each traffic class separately on the interface.

Question 15

Which IOS XR feature allows an administrator to grant specific commands to a user based on their role, using task groups?

Accepted Answer

Role-based access control (RBAC) with task groups. IOS XR's role-based access control (RBAC) uses task groups to bundle specific CLI commands and permissions, which are then assigned to user groups and users. This lets an administrator grant granular command-level access — for example, allowing a NOC user to run 'show' commands but not 'configure' — without giving full administrative rights. Task groups are the mechanism that maps roles to permitted tasks.

Answer

SNMPv3

Answer

IP access lists

Answer

AAA with RADIUS