350-501 Architecture Practice Test 8 — 15 Questions

Question 1

A service provider is implementing Segment Routing (SR) with MPLS. Which three statements are true regarding SR-MPLS? (Choose three.)

Accepted Answer

SR-MPLS does not require LDP or RSVP-TE. B is correct because SR-MPLS uses the MPLS data plane but replaces the control plane protocols LDP and RSVP-TE with IGP extensions (IS-IS or OSPF) to distribute segment information. This eliminates the need for these traditional label distribution protocols, simplifying network operations and reducing protocol overhead.

Answer

SR-MPLS supports traffic engineering only with a central controller

Answer

Adjacency SIDs are advertised via BGP-LS

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. Based on the exhibit, what is the most likely reason for no label bindings?

Accepted Answer

The remote peer has label filtering applied. The exhibit shows that the local router has not received any label bindings from the remote peer (as evidenced by the empty 'show mpls ldp bindings' output), which indicates that the remote peer is not advertising labels. This is typically due to an outbound label filtering policy applied on the remote peer, such as 'mpls ldp neighbor [neighbor-id] label-filter' or 'mpls ldp label-filter' that rejects label advertisements to the local router. The local router's LDP session may be established (based on 'show mpls ldp neighbor'), but the remote peer is actively preventing label distribution.

Answer

The local router has disabled label advertisements

Answer

The IGP routes are not present in the routing table

Answer

The LDP session is not fully established

Question 4

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 5

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.. The most common reason LDP fails to establish after global and interface configuration is that the interface is not enabled for MPLS forwarding. The command 'mpls ip' on the interface is required to activate LDP hello messages and label binding on that link. Without it, LDP remains disabled on the interface even if LDP is enabled globally and OSPF is working.

Answer

The LDP password matches.

Answer

The router-id is a loopback.

Answer

The IGP metric is set.

Question 6

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 7

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 8

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.. In a Carrier Supporting Carrier (CSC) architecture, the provider carrier's MPLS backbone must be able to forward packets toward the BGP next-hop of the customer carrier's routes. For this to happen, the BGP next-hop (typically a loopback interface on the customer carrier's PE router) must be reachable via an IGP (e.g., OSPF or IS-IS) running within the provider carrier's core. Without IGP reachability to that next-hop, the provider carrier's P routers cannot perform MPLS label switching to deliver traffic to the customer carrier's egress router, breaking end-to-end connectivity.

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 9

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 10

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 11

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 12

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 13

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.. Segment Routing (SR) uses a centralized control plane (via PCE or BGP-LS) to allocate labels per prefix, unlike LDP which allocates labels per interface on a hop-by-hop basis. This reduces the number of labels in the control plane and simplifies label management, as SR-MPLS uses a single label stack entry per segment rather than per-interface labels.

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 14

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

Accepted Answer

EVI (Ethernet VPN Instance). In EVPN VPWS, two parameters must match between endpoints: the EVI (Ethernet VPN Instance) must match because it defines the EVPN instance and the Route Distinguisher. The Route-target must also match because it ensures that routes are imported/exported correctly between the endpoints. The ESI (Ethernet Segment Identifier) is local to each PE and does not need to match; it identifies the local segment for split-horizon and DF election purposes.

Answer

ESI (Ethernet Segment Identifier)

Answer

VLAN ID of the attachment circuit

Answer

IMET group address

Question 15

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

Accepted Answer

LDP. LDP (Label Distribution Protocol) is a standardized protocol (RFC 5036) specifically designed for label distribution in MPLS networks. It operates by discovering LDP peers and exchanging label mappings for each FEC (Forwarding Equivalence Class), enabling label-switched path (LSP) establishment without requiring a routing protocol to carry label information.

Answer

OSPF

Answer

IS-IS