350-501 Architecture Practice Test 12 — 15 Questions

Question 1

A service provider is building a new network slicing architecture to offer differentiated services to enterprise customers. The architecture uses SRv6 with network slices identified by slice IDs embedded in the SRv6 SID. The underlay is an IP network with ISIS. Each slice will have dedicated resources in the core, including guaranteed bandwidth and low latency. The plan is to use the SRv6 network programming concept to steer traffic into different slices. The provider wants to ensure that slice isolation is maintained end-to-end, including at the egress PE where traffic is handed off to the customer. However, during testing, they observe that traffic from one slice is incorrectly entering another slice's queue on an intermediate node, causing performance interference. The intermediate node is a transit router that does not terminate SRv6 but performs 'SID-based forwarding'. Which mechanism is most likely missing to ensure slice isolation on transit nodes?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

The transit nodes are not configured to enforce per-slice QoS policies based on the slice ID in the SID.. On a transit router that only performs SRv6 SID-based forwarding (does not terminate the SID), slice isolation depends on the node enforcing per-slice QoS/queueing policies keyed to the slice ID carried in the SID. Without that enforcement, packets from different slices share the same forwarding queue and interfere, which matches the observed symptom.

Answer

The SRv6 SID does not carry the slice ID; it only carries the locator.

Answer

The egress PE is misconfigured to strip the slice ID before forwarding.

Answer

The ingress PE is not setting the slice ID correctly.

Question 2

A service provider offers IPTV services using multicast. The network uses Multicast VPN (MVPN) with Rosen GRE encapsulation (Profile 1) in an MPLS L3VPN environment. The Provider Edge (PE) routers participate in both the default MDT and data MDT for high-bandwidth streams. Recently, a new channel was added, and it uses a data MDT. The content server is attached to a PE that is acting as a multicast source. Other PEs are receivers. Upon adding the channel, some receivers report missing packets. The network engineer checks the PEs and notices that the data MDT group address is being advertised via BGP as an MDT SAFI route, but some PEs are not joining the data MDT. The source PE's multicast routing table shows that it believes data MDT is active. Which architecture issue is most likely preventing some PEs from joining the data MDT?

Accepted Answer

The data MDT group is not within the configured data MDT group range on the receiving PEs.. In MVPN with Rosen GRE (Profile 1), data MDT groups are configured on PE routers with a specific range. If a receiving PE does not have the data MDT group address within its configured data MDT group range, it will not join that data MDT even though the source PE advertises it via BGP MDT SAFI. This mismatch prevents the receiver from receiving multicast traffic on the data MDT, causing packet loss for high-bandwidth streams.

Answer

The source PE is not sending IGMP joins for the data MDT group.

Answer

The default MDT group is flapping.

Answer

The PIM sparse mode RP is not reachable.

Question 3

A network architect is designing a Segment Routing (SR) network for a service provider with a requirement for fast convergence upon node failure. The network uses IS-IS as the IGP with segment routing extensions. Which design choice BEST ensures that the network can achieve sub-50ms convergence without relying on any signaling protocol beyond the IGP?

Accepted Answer

Enable TI-LFA (Topology Independent Loop-Free Alternate) on all ISIS interfaces. TI-LFA (Topology Independent Loop-Free Alternate) is an SR IGP-based fast reroute mechanism that pre-computes backup paths for any topology change, providing sub-50ms convergence without additional signaling protocols like RSVP-TE. It leverages the IGP's link-state database and segment routing to create a loop-free alternate that is guaranteed to be loop-free for any failure, using the post-convergence path as the backup. This meets the requirement of relying only on the IGP.

Answer

Deploy BFD with static routes for fast detection

Answer

Configure RSVP-TE with Fast Reroute on all label-switched paths

Answer

Use LDP with LDP FRR and path protection

Question 4

A service provider needs to offer L3VPN services to multiple customers, each with overlapping IP addresses. The provider plans to use MPLS VPNs with VRFs. Which statement is TRUE regarding the configuration of VRFs on the PE routers?

Accepted Answer

Route targets (RTs) are used to control the import and export of VPNv4 routes between VRFs. Route targets (RTs) are extended BGP community attributes attached to VPNv4 routes that control which VRFs import and export those routes. In an MPLS L3VPN, the route distinguisher (RD) makes the customer prefix unique within the provider's BGP table, but it is the RT that determines the actual VPN membership and route leaking between VRFs. This allows overlapping customer IP addresses to be kept separate while still enabling controlled import/export policies.

Answer

The VRF must run OSPF to exchange routes with the CE router

Answer

MPLS labels are assigned per prefix inside a VRF by manual configuration

Answer

Each VRF must have a unique route distinguisher across the entire provider network

Question 5

A service provider has deployed QoS on its MPLS backbone to offer different classes of service. The provider notices that EF (Expedited Forwarding) traffic sometimes experiences high jitter during congestion. Following recommended practices, which action is MOST likely to reduce jitter for EF traffic?

Accepted Answer

Use priority queuing (LLQ) for EF traffic with a policer. Priority queuing (LLQ) with a policer ensures EF traffic is served strictly before other queues, reducing jitter, while the policer prevents EF traffic from monopolizing bandwidth. Option B is wrong because traffic shaping smooths bursts but does not provide priority treatment during congestion, so jitter can still occur. Option C is wrong because changing DSCP to AF41 would reclassify EF traffic to a lower priority class, potentially increasing jitter and delay. Option D is wrong because WRED is a congestion avoidance mechanism that drops packets randomly, which can cause jitter for EF traffic; EF should be exempt from WRED.

Answer

Apply traffic shaping on all EF packets at the edge

Answer

Change the DSCP value of EF traffic to AF41 to reduce drops

Answer

Apply weighted random early detection (WRED) on the EF queue

Question 6

Based on the exhibit, why is the route 10.10.10.0/24 from remote PE not installed in the VRF Customer-A on PE1?

Accepted Answer

The VRF imports route-target 200:200, but the route has RT 100:100. In MPLS L3VPN, route targets (RTs) control import and export of routes between VRFs. The VRF Customer-A on PE1 imports routes with RT 200:200, but the remote PE is exporting the route with RT 100:100. Since the RTs do not match, the route is not imported into the VRF. This is the reason the route is not installed.

Answer

The localpref is too low (100)

Answer

The MPLS label allocation failed on the remote PE

Answer

The route distinguisher on the VRF (100:1) does not match the remote RD

Question 7

Which access technology is commonly used in service provider networks to deliver high-speed internet over existing telephone lines?

Accepted Answer

DSL. DSL (Digital Subscriber Line) is the access technology specifically designed to deliver high-speed internet over existing copper telephone lines, using frequencies above the voice band so voice and data can coexist. It is the standard answer for 'high-speed internet over existing telephone lines' in service provider contexts.

Answer

Metro Ethernet

Answer

GPON

Answer

Cable

Question 8

In IOS XR architecture, what is the role of the Secure Domain Router (SDR)?

Accepted Answer

It provides isolation for routing protocols and forwarding tables.. An SDR provides a logical partitioning of router resources, allowing multiple independent virtual routers within a single physical chassis.

Answer

It handles all packet forwarding in hardware.

Answer

It is used for OSPF only.

Answer

It manages the admin plane for all line cards.

Question 9

A service provider is deploying L3VPN using BGP/MPLS. Which mechanism ensures customer isolation in the provider network?

Accepted Answer

Virtual Routing and Forwarding (VRF). Virtual Routing and Forwarding (VRF) creates separate routing tables on the same physical router, ensuring that customer routes are isolated from one another. Each VRF maintains its own RIB and FIB, so packets from one customer cannot be forwarded using another customer's routing information. This is the fundamental mechanism for customer isolation in BGP/MPLS L3VPN.

Answer

Pseudowire

Answer

MP-BGP

Answer

MPLS labels

Question 10

In IOS XR, what is the commit/rollback configuration model?

Accepted Answer

Configuration changes are staged and committed atomically; rollback is supported.. The commit/rollback model applies changes atomically and allows reverting to previous configurations if needed.

Answer

It requires a reboot to apply changes.

Answer

Changes are applied immediately and cannot be undone.

Answer

It only applies to interface configurations.

Question 11

A service provider wants to provide point-to-point Ethernet services with strict SLAs. Which technology should they use?

Accepted Answer

VPWS. VPWS (Virtual Private Wire Service) or pseudowire provides a point-to-point Ethernet connection over MPLS.

Answer

EVPN

Answer

L3VPN

Answer

VPLS

Question 12

Which MEF service type provides a point-to-point Ethernet connection between two user-network interfaces (UNIs)?

Accepted Answer

E-Line. MEF (Metro Ethernet Forum) defines E-Line as a point-to-point Ethernet service that connects exactly two UNIs, providing a dedicated Ethernet Virtual Connection (EVC) between them. It is the MEF equivalent of a leased line or Ethernet private line, and is used for site-to-site connectivity.

Answer

E-LAN

Answer

E-Tree

Answer

E-Access

Question 13

What is the main benefit of using Q-in-Q (802.1ad) in metro Ethernet networks?

Accepted Answer

Increases the number of available VLANs. Q-in-Q allows multiple customer VLANs to be encapsulated within a service provider VLAN, increasing scalability.

Answer

Simplifies routing

Answer

Provides encryption

Answer

Reduces latency

Question 14

In EVPN, what is the function of the Ethernet Segment Identifier (ESI)?

Accepted Answer

It identifies a multi-homed device or network segment.. The ESI identifies a multi-homed device or network, enabling all-active redundancy and fast convergence.

Answer

It is used for load balancing among PEs.

Answer

It uniquely identifies a customer MAC address.

Answer

It identifies a VXLAN tunnel.

Question 15

A service provider is deploying network slicing for 5G services. Which slice type is characterized by low latency and high reliability for applications like autonomous driving?

Accepted Answer

uRLLC. uRLLC (Ultra-Reliable Low-Latency Communication) is the 5G slice type specifically designed for mission-critical applications requiring sub-millisecond to a few-millisecond latency and 99.999% reliability, such as autonomous driving, remote surgery, and industrial automation. It is one of the three canonical 5G service categories defined by ITU-R IMT-2020.

Answer

FMC

Answer

eMBB

Answer

mMTC