350-501 Architecture Practice Test 11 — 15 Questions

Question 1

A service provider is experiencing suboptimal routing due to BGP route reflection. To improve path selection while maintaining IBGP scalability, which feature should be implemented?

Accepted Answer

BGP optimal route reflection (ORR). BGP optimal route reflection (ORR) improves path selection by allowing the route reflector to calculate the best path based on the IGP metric to the client's location, rather than using its own BGP table. This overcomes the suboptimal routing caused by standard route reflection, where the RR's best path may not be optimal for all clients, while still maintaining IBGP scalability by avoiding a full mesh.

Answer

BGP deterministic med

Answer

BGP next-hop-self

Answer

BGP add-path

Question 2

Refer to the exhibit. A PE router configuration for VRF CUST1 is shown. What is the most likely result when a CE sends a route with RT 100:100?

Accepted Answer

The route is received but not imported into VRF. The VRF CUST1 configuration does not include a route-target import statement for RT 100:100. Without a matching import RT, the PE router will receive the route from the CE but will not import it into the VRF. The route is received (BGP update is accepted) but not installed in the VRF routing table, making option D correct.

Answer

The route causes a BGP session reset

Answer

The route is imported and installed in VRF

Answer

The route is imported but not advertised to other CEs

Question 3

Refer to the exhibit. An engineer has configured an SR-TE policy. What is required for this policy to be used for traffic steering?

Accepted Answer

BGP with color extended community. An SR-TE policy uses a color extended community to identify the policy's color and its associated endpoint. BGP distributes these color extended communities, enabling headend routers to match traffic to the correct SR-TE policy for steering. Without BGP carrying the color extended community, the policy cannot be dynamically selected for traffic engineering.

Answer

Static routing

Answer

IGP with segment routing

Answer

OSPF with opaque LSA

Question 4

A service provider is deploying EVPN-VPWS for point-to-point services. They have set up an EVPN instance with Ethernet Segment Identifier (ESI) and EVI. After configuration, the pseudowire is not coming up. Which misconfiguration is most likely?

Accepted Answer

The BGP EVPN address-family is not activated.. In EVPN-VPWS, the EVI (EVPN Instance) must be the same on both PEs for the same point-to-point service to ensure proper route matching and label assignment. Therefore, using the same EVI is correct and not a misconfiguration. The most likely issue is that the BGP EVPN address-family is not activated on the PEs. Without this address-family, the PEs cannot exchange EVPN routes (e.g., Type 1 per-EVI AD routes), so the pseudowire cannot be established. The other options—ESI all-zeros (acceptable for single-homed) and MTU mismatch (would cause operational issues but not prevent pseudowire from coming up at the control-plane level)—are less likely to be the root cause.

Answer

The same EVI is used on both PEs.

Answer

The ESI is all-zeros.

Answer

The MTU mismatch on the attachment circuits.

Question 5

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

Question 6

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 7

In a carrier network using VRF-lite for customer isolation, which issue arises if route-target values are not correctly configured?

Accepted Answer

Customer routes leak into other VRFs.. In VRF-lite, route-target (RT) values control the import and export of routes between VRFs. If RTs are misconfigured, a VRF may import routes intended for another VRF, causing customer routes to leak across VRFs. This violates isolation because the VRF table incorrectly accepts routes based on mismatched RT import statements.

Answer

Customer routes are not installed in the global table.

Answer

BGP sessions between PEs flap.

Answer

The PE-CE routing protocol fails.

Question 8

In an SR network, which configuration is required to activate TI-LFA for link protection?

Accepted Answer

fast-reroute per-prefix ti-lfa under the IGP process. TI-LFA (Topology Independent Loop-Free Alternate) is activated under the IGP process using the 'fast-reroute per-prefix ti-lfa' command. This enables segment routing to compute a backup path that provides link protection without relying on the topology of the failure, ensuring 50-msec convergence.

Answer

metric delay interface configuration

Answer

label-preferred under the interface

Answer

mpls traffic-eng auto-tunnel primary

Question 9

An SP is managing a large MPLS network and needs to verify the MPLS forwarding entries for a specific VRF. Which command provides the most complete information for the VRF?

Accepted Answer

show mpls forwarding-table vrf . The 'show mpls forwarding-table vrf ' command displays the complete MPLS forwarding entries for a specific VRF, including the incoming label, outgoing label, next-hop, and outgoing interface. This command is specifically designed to verify MPLS label-switched paths (LSPs) for a VRF, which is essential for troubleshooting MPLS VPN forwarding. It provides the most complete information for MPLS forwarding, as it shows both the label operations (swap, pop, push) and the VRF-specific forwarding details.

Answer

show ip cef vrf <name>

Answer

show mpls vrf <name>

Answer

show bgp vpnv4 unicast all labels

Question 10

Which THREE protocols are used for label distribution in an MPLS network?

Accepted Answer

LDP. LDP (Label Distribution Protocol) is correct because it is the primary protocol designed specifically to distribute MPLS labels between Label Switch Routers by mapping FECs to labels. BGP is correct because it can distribute MPLS labels along with BGP routes, notably in BGP/MPLS IP VPNs (RFC 4364) using the labeled-unicast address family and extended communities for VPN labels. RSVP is correct because RSVP-TE (RSVP with Traffic Engineering extensions) distributes labels when establishing traffic-engineered LSPs via PATH and RESV messages. OSPF and IS-IS are not label distribution protocols; they are link-state interior gateway routing protocols that can carry MPLS-related extensions (e.g., for TE) but do not themselves distribute labels.

Answer

OSPF

Answer

IS-IS

Question 11

A service provider offers L3VPN services to multiple enterprise customers. One customer reports that they cannot reach some remote sites intermittently. The network uses MPLS L3VPN with MP-BGP for VPN route exchange. The PE routers are configured with route-target import and export. The customer's CE router is dual-homed to two different PEs in the same point of presence. The engineer checks the BGP table on both PEs and sees the customer routes with the correct route-target. However, pings from the CE to a remote site fail about 50% of the time, and the flapping pattern suggests load balancing issues. The engineer discovers that the remote site's network prefix is being advertised from both PEs with the same route-target but with different next-hops. The CE has equal-cost paths via both PEs. What is the most likely cause of the intermittent connectivity?

Accepted Answer

The CE is performing per-packet load balancing across the two PEs, causing asymmetric routing.. The CE is dual-homed to two PEs and has equal-cost paths, and the intermittent 50% failure pattern is the signature of per-packet load balancing causing asymmetric routing. When the CE load-balances per packet across both PEs, packets for the same flow can traverse different PEs, and if the remote PE or firewall performs stateful inspection or if return paths differ, some packets are dropped. The correct fix is to use per-destination (per-flow) load balancing so a flow sticks to one path.

Answer

The route-target import on the remote PE is missing the customer's route-target.

Answer

The BGP timers are misconfigured, causing the session to flap.

Answer

The MTU on the CE-PE links is mismatched.

Question 12

A service provider is implementing EVPN for its VPLS replacement. They have configured BGP EVPN on all PEs and have set up an EVPN instance for a customer requiring broadcast, unknown unicast, and multicast (BUM) traffic. The customer reports that broadcast traffic from one site is not being received at another site. The engineer checks the EVPN configuration and finds that the EVI is configured correctly, the route-target matches, and the BGP sessions are established. The engineer also checks the MAC address table on the receiving PE and sees that the source MAC of the broadcast frame is learned on the local interface, but not from the remote VTEP. The engineer suspects an issue with the IMET (Inclusive Multicast Ethernet Tag) route. Which action should the engineer take to verify the IMET route?

Accepted Answer

Check the BGP EVPN route table for IMET (route-type 3) routes using 'show bgp l2vpn evpn route-type 3'.. In BGP EVPN, the IMET (Inclusive Multicast Ethernet Tag) route is a Type-3 route used to build the multicast tunnel for BUM (broadcast, unknown unicast, multicast) traffic. If BUM traffic from one site is not reaching another, and the MAC table shows the source MAC learned locally but not from the remote VTEP, the IMET route is likely missing or not being advertised/received. The correct verification is to inspect the BGP EVPN route table specifically for Type-3 routes using 'show bgp l2vpn evpn route-type 3'.

Answer

Use 'show evpn instance detail' to check the EVI configuration.

Answer

Use 'show bgp l2vpn evpn route-type 2' to verify MAC/IP routes.

Answer

Use 'show l2vpn vfi' to verify the VPLS forwarding instance.

Question 13

A service provider is designing an MPLS L3VPN network to provide Layer 3 VPN services to multiple customers. Which two statements correctly describe the roles of the Provider Edge (PE) and Customer Edge (CE) routers in this architecture?

Accepted Answer

PE routers advertise customer routes via MP-BGP with route distinguishers and route targets.. Option C is correct because in an MPLS L3VPN, PE routers use MP-BGP (multiprotocol BGP, specifically the VPNv4/VPNv6 address families) to advertise customer routes across the provider backbone, and each route is tagged with a Route Distinguisher (RD) to make the prefix unique and Route Targets (RTs) to control import/export into the correct VRFs. Option E is correct because each PE router maintains separate VRF (Virtual Routing and Forwarding) tables per customer VPN, isolating customer routing information and allowing overlapping address spaces between different customers. Option A is incorrect because P (provider core) routers only forward labeled packets and do not store customer VPN routes; they typically hold only the provider's global/IGP routes and label bindings. Option B is incorrect because CE routers are customer-owned devices that do not run MPLS label switching between PEs; label imposition/disposition and VPN label switching occur on the PE routers. Option D is incorrect because CE routers do not participate in the service provider's IGP; the PE-CE routing exchange uses a separate routing protocol or static routes within the VRF, not the provider's core IGP.

Answer

P routers store all customer VPN routes in their global routing table.

Answer

CE routers perform MPLS label switching between PE routers.

Answer

CE routers participate in the service provider's IGP to exchange loopback addresses.

Question 14

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.. Option B is correct because an Adjacency SID is a local segment that a router allocates to represent a specific adjacency/link to a neighbor, and it is only meaningful on the advertising router (typically advertised via IS-IS SR extensions with a local significance flag). Option C is correct because a Prefix SID is a globally significant segment that identifies a specific IGP prefix (such as a loopback) and is derived from the router's SRGB, allowing any node in the SR domain to reach that prefix via the corresponding MPLS label. Option E is correct because SIDs are allocated from the Segment Routing Global Block (SRGB) and distributed through the IGP's SR extensions — in this scenario IS-IS — so that all routers can build the SR-MPLS forwarding table. Option A is wrong because OSPF (OSPFv2/OSPFv3) does support SR extensions and can be used for SR-MPLS, so the claim that it cannot is false. Option D is wrong because the SRGB does not have to be identical across all routers; what matters is that the resulting global SID/label values are unique and consistently interpreted, which is achieved through the SRGB base plus index mapping, not by requiring identical SRGB ranges on every router.

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 15

A service provider offers Carrier Ethernet services using MPLS-TP in the access and aggregation layers. The network uses MPLS-TP tunnels with static LSPs and protection via 1:1 linear protection with APS. One customer reports intermittent connectivity issues on their E-LINE service. The operations team observes that the protection switchover is occurring frequently due to apparent signal failures on the working path. However, the physical layer shows no errors. The protection switching is configured with revertive mode. The working LSP has an RDI (Remote Defect Indication) configured. Upon further investigation, the team finds that the working LSP's OAM continuity check messages (CCMs) are being lost occasionally, triggering a protection switch. What is the most likely misconfiguration?

Accepted Answer

The CCM interval is too short, causing frequent false failures due to transient congestion.. In MPLS-TP OAM, continuity check messages (CCMs) are sent at a configured interval. If the interval is too short, the protection mechanism may interpret transient congestion or minor delays as a signal failure, triggering frequent protection switches. Since the physical layer shows no errors, the issue is likely that the CCM interval is too aggressive for the network conditions, causing false positives.

Answer

The CCM interval is too long, causing delayed detection.

Answer

The working path uses a higher MPLS-TP OAM rate than the protection path.

Answer

The protection path has a lower priority than the working path.