350-501 Practice Test 34 — 15 Questions

Question 1

A network engineer is troubleshooting OSPFv3 on a service provider's IPv6 network. The router shows that OSPFv3 adjacency never reaches FULL, says 'Init'. The neighbor is directly connected over a point-to-point link. What is the most likely cause?

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

Accepted Answer

Missing 'ipv6 ospf' interface command on one side. The 'Init' state in OSPFv3 indicates that the router has received a Hello packet from the neighbor but the neighbor has not received a Hello packet back. On a point-to-point link, the most common cause is that the 'ipv6 ospf area ' interface command is missing on one side, which prevents OSPFv3 from sending Hellos on that interface. Without this command, the interface is not enabled for OSPFv3, so the neighbor never sees a Hello and the adjacency cannot progress to FULL.

Answer

LSA throttling prevents exchanges

Answer

Mismatched OSPF router-id

Answer

Mismatched area IDs

Question 2

A service provider is implementing MPLS in their core network. They want to ensure that labeled packets for BGP prefixes are forwarded correctly without requiring an IGP label for every BGP prefix. Which technique should be used to achieve this?

Accepted Answer

Use BGP-free core with LDP or Segment Routing. A BGP-free core with LDP or Segment Routing allows the service provider to forward labeled packets for BGP prefixes without requiring an IGP label for every BGP prefix. In this design, edge routers (PEs) impose a label stack where the outer label (IGP label) is distributed by LDP or Segment Routing for the BGP next-hop, and the inner label is the BGP label. Core routers (P routers) only need to swap the outer label based on the IGP label, not the BGP prefix, thus eliminating the need for IGP labels per BGP prefix.

Answer

Enable MPLS on all interfaces and rely on BGP label distribution

Answer

Implement LDP for BGP prefixes

Answer

Configure static labels for BGP prefixes

Question 3

Which two MPLS OAM tools can be used to troubleshoot label switching paths? (Choose two)

Accepted Answer

MPLS LSP ping. MPLS LSP ping (option C) is an OAM tool specifically designed to verify the data plane of an MPLS label switched path (LSP) by sending an MPLS echo request packet with a target FEC stack, which is forwarded along the LSP and validated by the egress LSR. This tests the actual label forwarding path, not just the control plane, making it a correct choice for troubleshooting LSPs.

Answer

traceroute

Answer

show ip route

Answer

ping

Question 4

In a Layer 3 MPLS VPN, a customer site that is part of VRF RED is unable to communicate with another site that is also in VRF RED. The 'show ip bgp vpnv4 vrf RED' command shows the routes, but the router does not install them in the routing table. Which configuration element is most likely missing?

Accepted Answer

The route-target import on the receiving PE.. In a Layer 3 MPLS VPN, VRF RED routes are learned via MP-BGP between PEs. The 'show ip bgp vpnv4 vrf RED' command confirms the routes are present in the BGP table, but they are not installed in the routing table because the receiving PE lacks the correct route-target import configuration. The route-target import statement on the VRF determines which VPNv4 routes are accepted and installed into the VRF's RIB; without it, the routes remain in BGP but are not added to the routing table.

Answer

A BGP session between PEs.

Answer

The route-target export on the receiving PE.

Answer

An MPLS LDP session between PEs.

Question 5

Which TWO MPLS VPN features are used to provide Layer 3 VPN services in a service provider network?

Accepted Answer

MPLS labels. MP-BGP (Option E) is used to exchange VPNv4 routes between Provider Edge (PE) routers, carrying both the route and its corresponding MPLS label. MPLS labels (Option C) are used to forward packets across the provider core via label-switched paths (LSPs), enabling the separation of customer traffic. Together, MP-BGP and MPLS labels form the foundation of Layer 3 MPLS VPN services.

Answer

LDP

Answer

VRF

Answer

RSVP-TE

Question 6

Which three of the following are valid methods for protecting a pseudowire in an MPLS network?

Accepted Answer

Multi-segment PW with backup. Multi-segment PW (MS-PW) with backup is a valid protection method because it allows a pseudowire to be established across multiple MPLS segments, with a backup PW path that can take over if the primary MS-PW fails. This provides end-to-end pseudowire redundancy by using a secondary switched path, ensuring service continuity in multi-domain or multi-area MPLS networks.

Answer

Ethernet OAM CFM

Answer

LSP ping for fault detection

Question 7

In SRv6, which endpoint behavior is used for decapsulation and forwarding to a Layer 3 VPN IPv4 destination, removing the outer IPv6 header?

Accepted Answer

End.DT4. End.DT4 is the SRv6 endpoint behavior for decapsulation and table lookup in the VPN IPv4 table.

Answer

End.X

Answer

End.DT6

Answer

End.DT2U

Question 8

Refer to the exhibit. The router is configured as a route reflector for VPNv4. What is the requirement for the route reflector to propagate VPNv4 routes received from a client to other clients?

Accepted Answer

The route reflector must include the originator ID attribute to prevent loops. The route reflector must include the originator ID attribute to prevent routing loops when reflecting VPNv4 routes between clients. The originator ID is set to the router ID of the originating IBGP speaker, and the route reflector ignores any route with an originator ID equal to its own router ID, thereby preventing loops in a client-to-client reflection scenario.

Answer

The route reflector must filter routes based on route-target communities

Answer

The route reflector must use the same cluster ID for all clients

Answer

The route reflector must set the next-hop to itself for all reflected routes

Question 9

A service provider is deploying IS-IS with wide metrics to support traffic engineering. Which two statements about IS-IS wide metrics are correct?

Accepted Answer

Wide metrics use TLV 135 for extended IS reachability.. Wide metrics use a 24-bit or 32-bit field, allowing values up to 16,777,215 or more, and are backward compatible with narrow metrics via apportioning.

Answer

Wide metrics are required for segment routing.

Answer

Wide metrics are incompatible with narrow metrics and require a full migration.

Answer

Narrow metrics can only be used with L1 routing.

Question 10

A large SP plans to deploy SR-TE tunnels across the backbone using an SDN controller for path computation. To ensure fast convergence and scalability, which automation approach should be used for tunnel creation?

Accepted Answer

PCEP with stateful delegation to controller. B is correct because PCEP with stateful delegation allows the SDN controller to compute and instantiate SR-TE tunnels dynamically, while the router delegates control to the controller for path updates. This approach ensures fast convergence by enabling the controller to react to network changes in real time and scales efficiently by centralizing path computation, avoiding per-router configuration overhead.

Answer

Static configuration on each router

Answer

RSVP-TE tunnels

Answer

NetFlow-based path selection

Answer

SNMP traps

Question 11

Which TWO are characteristics of Segment Routing (SR-MPLS)? (Choose two.)

Accepted Answer

It relies on source routing. Segment Routing (SR-MPLS) is a source routing paradigm where the ingress node encodes a list of segment identifiers (SIDs) into the packet header, specifying the path the packet must take through the network. This eliminates the need for per-hop signaling protocols like LDP or RSVP-TE, as each intermediate node simply forwards based on the top SID.

Answer

It requires a centralized controller for traffic engineering

Answer

It forwards packets based on destination IP address at each hop

Answer

It requires MPLS LDP for label distribution

Question 12

Which protocol is used to exchange label binding information in a classic MPLS network without Segment Routing?

Accepted Answer

LDP. In a classic MPLS network without Segment Routing, LDP (Label Distribution Protocol) is the standard protocol used to exchange label binding information. LDP assigns and distributes labels for each FEC (Forwarding Equivalence Class) based on the underlying IGP routing table, enabling label-switched paths (LSPs) without requiring RSVP or Segment Routing extensions.

Answer

OSPF

Answer

BGP

Answer

IS-IS

Question 13

A network administrator configures a class map to match VoIP traffic using 'match ip dscp ef' on a Cisco router. However, the QoS policy is not applying the expected marking to VoIP packets. What is a possible reason?

Accepted Answer

The VoIP traffic is not marked with DSCP EF from the source.. The 'match ip dscp ef' command in the class map checks the DSCP value already present in the incoming VoIP packets. If the source device (e.g., an IP phone) does not mark the packets with DSCP EF (46), the class map will not match, and the QoS policy will not apply the expected marking. The policy can only re-mark packets that are already matched by the class map.

Answer

The policy is applied in the output direction instead of input.

Answer

The policy is applied to the wrong interface.

Answer

The class map uses the wrong match type.

Question 14

Refer to the exhibit. An engineer makes a RESTCONF request to retrieve operational data for all interfaces, but the response shows only one interface. What is the most likely cause?

Accepted Answer

The request path includes a specific interface key, filtering the result. If the RESTCONF request path includes a specific interface key (e.g., /restconf/data/ietf-interfaces:interfaces/interface=GigabitEthernet0/0/0), the API will return only that single interface's operational data, even if the engineer intended to retrieve all interfaces. RESTCONF uses URI-encoded keys to filter resources; omitting the key returns the entire list, while including a key narrows the response to that specific instance.

Answer

The interfaces are in different VRFs

Answer

The device does not support the YANG model

Answer

The engineer used the wrong HTTP method

Answer

The collector is not subscribed to telemetry

Question 15

Which three BGP attributes are considered in the route selection process before comparing MED? (Choose three.)

Accepted Answer

Weight. The order: weight, local pref, originate (locally originated), AS_PATH length, ORIGIN, MED. So weight, local pref, and AS_PATH length are before MED.

Answer

MED

Answer

Router ID