350-501 Architecture Practice Test 8 — 15 Questions

Question 1

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. For an SR-TE policy to be used, traffic must be steered via BGP with a color extended community matching the policy's color. Without a match, the policy is not activated. Option B: IGP with SR is already configured; Option C: static routing is not relevant; Option D: OSPF opaque LSA is for OSPF extensions, not SR-TE policy activation.

Answer

Static routing

Answer

IGP with segment routing

Answer

OSPF with opaque LSA

Question 2

A network engineer is configuring MPLS LDP on a new router. After enabling LDP globally and on the interface, the LDP session does not establish. The IGP (OSPF) is fully operational. What should the engineer verify first?

Accepted Answer

The interface has 'mpls ip' enabled.. Option A is correct because the most basic check is whether the interface has 'mpls ip' enabled. Option B is wrong because LDP router-id can be any reachable IP, not necessarily a loopback. Option C is wrong because password mismatch would cause authentication failure, but the session might still attempt to establish. Option D is wrong because IGP metric does not affect LDP session establishment.

Answer

The LDP password matches.

Answer

The router-id is a loopback.

Answer

The IGP metric is set.

Question 3

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 same EVI is used on both PEs.. Option B is correct because for EVPN-VPWS, the same EVI must be used on both PEs to establish the pseudowire. Option A is wrong because a non-zero ESI is required, but all-zeros is invalid. Option C is wrong because BGP EVPN address-family is needed but its absence would affect all EVPN services, not just VPWS. Option D is wrong because MTU mismatch causes issues but is less likely than EVI mismatch.

Answer

The ESI is all-zeros.

Answer

The MTU mismatch on the attachment circuits.

Answer

The BGP EVPN address-family is not activated.

Question 4

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. Option C is correct because the 'segment-routing mpls' command must be enabled under the IS-IS router configuration to activate label allocation for segment routing. Option A is wrong because 'mpls label protocol sr' is not an IS-IS command; it is a global command. Option B is wrong because IS type does not affect segment routing directly. Option D is wrong because prefix-SID under the interface is for specific prefix assignments, not for enabling label allocation globally.

Answer

mpls label protocol sr

Answer

prefix-sid under the loopback interface

Answer

is-type level-1-2

Question 5

In a Carrier Supporting Carrier (CSC) architecture, which condition is necessary for the customer carrier's BGP routes to be carried over the provider carrier's MPLS backbone?

Accepted Answer

The BGP next-hop on the customer carrier's routes must be reachable via IGP in the provider carrier.. Option D is correct because in CSC, the customer carrier's BGP next-hop must be reachable via the provider carrier's IGP for label switching to work. Option A is wrong because AS numbers can be different; the provider carrier treats the customer carrier as a VPN. Option B is wrong because LDP is used for label distribution in the customer carrier's network, but it's not a condition for the provider carrier. Option C is wrong because the route-target is used for VPN route import/export, but CSC does not necessarily require a VRF on the provider carrier if using BGP-free core.

Answer

The provider carrier's VRF must have the route-target matching the customer carrier's.

Answer

The provider carrier must be in the same AS as the customer carrier.

Answer

The customer carrier must use LDP for label distribution.

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. Option A is correct because 'show mpls traffic-eng tunnels brief' displays the status, state, and role of all TE tunnels. Option B is wrong because 'show mpls ldp tunnels' shows LDP tunnel statistics, not TE tunnels. Option C is wrong because 'show ip rsvp reservation' shows RSVP reservations, which are used by TE but do not list tunnels. Option D is wrong because 'show mpls forwarding-table' shows the LFIB, not TE tunnel status.

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.. Option B is correct because incorrect route-target configuration can cause routes from one VRF to be imported into another VRF, leading to route leakage. Option A is wrong because routes would still be installed in the VRF, but they might leak. Option C is wrong because PE-CE routing protocols are independent of route-target. Option D is wrong because BGP sessions between PEs are not directly affected by VRF route-targets.

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. Option C is correct because the command 'fast-reroute per-prefix ti-lfa' under the IGP process (IS-IS or OSPF) explicitly enables TI-LFA. Option A is wrong because 'mpls traffic-eng auto-tunnel primary' is for TE auto-tunnel, not TI-LFA. Option B is wrong because 'label-preferred' is not a valid command. Option D is wrong because 'metric delay' is for IGP convergence, not TI-LFA.

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 . Option D is correct because 'show mpls forwarding-table vrf ' displays the label forwarding table for the VRF, including inbound and outbound labels. Option A is wrong because 'show ip cef vrf' shows CEF table, not MPLS labels. Option B is wrong because 'show bgp vpnv4 unicast all labels' shows BGP label bindings, not the forwarding table. Option C is wrong because 'show mpls vrf' is not a valid command.

Answer

show ip cef vrf <name>

Answer

show mpls vrf <name>

Answer

show bgp vpnv4 unicast all labels

Question 10

Which TWO are benefits of using Segment Routing over LDP in a service provider core?

Accepted Answer

Label allocation is per-prefix, not per-interface.. Options A and C are correct. SR supports TI-LFA for fast reroute, and native per-prefix label allocation. Option B is wrong because SR still requires IGP convergence for label distribution. Option D is wrong because SR can be used with TE, but LDP also supports TE. Option E is wrong because SR may actually increase the number of labels due to SID stack.

Answer

Reduces the number of labels in the control plane.

Answer

Eliminates the need for IGP convergence for label distribution.

Answer

Simplifies MPLS TE tunnel configuration.

Question 11

When configuring EVPN VPWS, which TWO parameters must match between the two endpoints of the pseudowire?

Accepted Answer

EVI (Ethernet VPN Instance). Options A and B are correct. EVI and ESI must match to form a pseudowire. Option C (IMET) is used for multicast but not for VPWS. Option D is not required to match; VLAN IDs can differ. Option E (route-target) is used for route import/export but not mandatory for VPWS endpoint matching.

Answer

Route-target

Answer

VLAN ID of the attachment circuit

Answer

IMET group address

Question 12

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

Accepted Answer

LDP. Options A, B, and C are correct. LDP, BGP, and RSVP are standard label distribution protocols. OSPF and ISIS are IGPs and do not distribute labels, although they can be used for SR, but SR still relies on IGP to advertise prefix-SIDs, not as a label distribution protocol per se.

Answer

OSPF

Answer

IS-IS

Question 13

A large service provider operates a national MPLS backbone with over 200 P routers and 500 PE routers. They use IS-IS as the IGP with segment routing and have deployed TI-LFA for link and node protection. Recently, a core router (P1) suffered a complete failure, and during the failure, traffic for some prefixes was dropped for over 200ms. After the failure, the network recovered within seconds. The engineer suspects that TI-LFA did not provide the expected sub-50ms protection for some destinations. Further analysis reveals that the affected prefixes have their BGP next-hop on a router that is multiple hops away, and the P1 failure impacted both the primary path and the backup path computed by TI-LFA. The engineer reviews the TI-LFA configuration and finds that 'fast-reroute per-prefix ti-lfa' is enabled under router isis. The engineer also notes that P1 was not a protecting node for those prefixes. Which action should the engineer take to improve convergence time for these prefixes?

Accepted Answer

Add the 'sr-protect' option under the fast-reroute configuration to enable node protection. Option B is correct because for TI-LFA to provide node protection, the 'sr-protect' option should be configured, which forces the node to attempt to provide protection even for traffic that transits through the node. Option A is wrong because interface-level TI-LFA would not help; the issue is node-level. Option C is wrong because increasing IGP timers may cause slower convergence. Option D is wrong because there is no need for an additional LDP backup.

Answer

Configure TI-LFA on all interfaces using 'fast-reroute per-prefix ti-lfa interface'

Answer

Reduce the IGP timers and enable incremental SPF to accelerate convergence

Answer

Deploy LDP as a fallback label distribution protocol to provide additional backup paths

Question 14

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.. Option C is correct because when a CE receives two equal-cost paths from two PEs, the CE may perform per-packet load balancing, which can cause out-of-order packets and asymmetric routing, leading to failures. Option A is wrong because BGP timers would cause immediate session drops, not 50% failure. Option B is wrong because MTU mismatch would cause consistent failures, not intermittent. Option D is wrong because route-target mismatch would prevent routes from being learned, not cause intermittent connectivity.

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 15

A small service provider is deploying MPLS in its core network for the first time. They have a simple topology: three P routers in the core and two PE routers connecting customers. They have configured LDP on all interfaces and OSPF as the IGP. They also configured a basic L3VPN for a customer with a single CE attached to each PE. The customer reports that they can ping between CEs for a few minutes, but then the connectivity drops. After a few seconds, it returns. This pattern repeats every few minutes. The engineer checks the LDP neighbors and sees that all LDP sessions are up. The OSPF adjacencies are stable. The engineer also notices that the pings time out exactly when the LDP graceful restart timer is expiring on one of the P routers. What is the most likely cause?

Accepted Answer

The BGP session between the PEs is flapping due to a hold timer mismatch or connectivity issue.. Option D is correct because if the BGP session between PEs is going down (e.g., due to a hold timer issue or misconfiguration), the VPN routes would be withdrawn and re-advertised, causing intermittent connectivity. Option A is wrong because LDP graceful restart timer is for LDP session recovery, but LDP sessions are up. Option B is wrong because OSPF network type does not cause periodic drops. Option C is wrong because interface flaps would cause more permanent outages.

Answer

The LDP graceful restart timer is causing periodic re-establishment of LDP sessions.

Answer

The OSPF network type on the core links is set to point-to-point, causing SPF recalculation every 5 minutes.

Answer

One of the core interfaces is flapping due to a hardware issue, triggering IGP and LDP convergence.

350-501 Architecture Practice Test 8 — 15 Questions

Exhibit

350-501 Architecture Practice Test 8 — 15 Questions

Exhibit