350-501 Services Practice Test 3 — 15 Questions

Question 1

A service provider deploys MPLS L3VPN to connect multiple customer sites. Which VPN address family must be enabled on the PE routers to exchange customer IPv4 routes between PEs?

Accepted Answer

VPNv4 unicast. In an MPLS L3VPN, customer IPv4 routes must be transported between Provider Edge (PE) routers across the MPLS backbone. The VPNv4 unicast address family (AF 1, SAFI 128) is required because it carries both the IPv4 prefix and an 8-byte Route Distinguisher (RD), making routes unique across different VPNs. This address family is enabled under the BGP configuration on PE routers (e.g., `address-family vpnv4 unicast`) to exchange labeled VPN routes using MP-BGP, as defined in RFC 4364.

Answer

IPv4 labeled-unicast

Answer

IPv4 unicast

Answer

VPNv6 unicast

Question 2

A network engineer is troubleshooting slow BGP convergence after a link failure in an MPLS core. Which feature can be enabled on the PE routers to fast-failover traffic upon BGP next-hop unreachability?

Accepted Answer

BGP Prefix Independent Convergence (PIC). BGP Prefix Independent Convergence (PIC) enables fast failover by pre-installing backup paths into the forwarding table, so when a BGP next-hop becomes unreachable, traffic is immediately switched to the backup path without waiting for BGP reconvergence. This is critical in MPLS cores where slow BGP convergence after a link failure can cause prolonged traffic loss.

Answer

Route Reflector clustering

Answer

Bidirectional Forwarding Detection (BFD)

Answer

Local Preference manipulation

Question 3

Refer to the exhibit. CE1 is unable to ping the loopback of a remote CE. Which configuration change is required on PE1 to enable communication?

Accepted Answer

Apply the VRF to the interface facing CE and ensure BGP VRF neighbor is activated. The configuration is missing the VRF forwarding statement on the interface facing CE1 and the BGP VRF neighbor activation under the VRF address-family. Without applying the VRF to the interface, PE1 cannot associate the CE-facing interface with the correct VRF, and without activating the BGP neighbor under the VRF address-family, PE1 will not establish a BGP session with CE1 or exchange routes for that VRF. This prevents CE1 from learning the remote CE's loopback route.

Answer

Add `send-community extended` to the VRF BGP neighbor

Answer

Change the VPNv4 neighbor to point to 192.168.1.2

Answer

Set the CE neighbor remote-as to 65000

Question 4

A customer requires MPLS Layer 2 VPN connectivity between two sites using Pseudowire. Which control protocol is used to signal the pseudowire label?

Accepted Answer

LDP. B is correct because LDP (Label Distribution Protocol) is the standard control protocol used to signal pseudowire labels in MPLS Layer 2 VPNs. Specifically, the Targeted LDP (T-LDP) session between the two Provider Edge (PE) routers exchanges the Virtual Circuit (VC) label, which is the inner label used to identify the pseudowire. This is defined in RFC 4447 and is the default signaling mechanism for AToM (Any Transport over MPLS).

Answer

RSVP-TE

Answer

BGP

Answer

OSPF

Question 5

Which technology allows a service provider to offer different classes of service over a single MPLS network?

Accepted Answer

QoS. QoS (Quality of Service) enables a service provider to differentiate traffic by marking packets with specific DSCP or IP precedence values and applying policies such as policing, shaping, and queuing. This allows multiple classes of service (e.g., voice, video, best-effort) to be carried over a single MPLS network while guaranteeing bandwidth, latency, and jitter requirements for each class.

Answer

BGP

Answer

LDP

Answer

MPLS VPN (VRF)

Question 6

Refer to the exhibit. A network engineer applies this policy on the PE-CE link. What is the expected behavior for VoIP traffic matching the access list?

Accepted Answer

VoIP traffic is given strict priority queuing with up to 30% bandwidth. The policy-map applies the 'priority' command to the VoIP class, which enables strict priority queuing (LLQ). The 'police cir percent 30' command limits the priority queue's bandwidth to 30% during congestion, ensuring VoIP traffic is always served first but cannot exceed the configured percentage. This matches option A exactly.

Answer

VoIP traffic is dropped if congestion occurs

Answer

VoIP traffic is shaped to 30% of bandwidth

Answer

VoIP traffic is queued in the default class with fair-queue

Question 7

During a multicast deployment, some receivers are not receiving the stream. The PIM neighbor table shows the upstream interface is correct. Which command would verify whether the multicast routing table has the correct outgoing interface list?

Accepted Answer

show ip mroute. The 'show ip mroute' command displays the multicast routing table, including the outgoing interface list (OIL) for each multicast group. Since the PIM neighbor table confirms the upstream interface is correct, the issue likely lies in the OIL, which 'show ip mroute' directly verifies. This command shows which interfaces are forwarding multicast traffic and whether they are pruned or in a forwarding state.

Answer

show ip igmp groups

Answer

show ip pim neighbor

Answer

show ip route

Question 8

A service provider wants to provide Internet access to an MPLS L3VPN customer without leaking the Internet route into the VRF. Which feature allows the PE to forward traffic from the VRF to the global routing table?

Accepted Answer

NAT with VRF awareness. NAT with VRF awareness (also known as VRF-aware NAT) allows the PE router to translate the private source IP address of traffic from the VRF to a public IP address in the global routing table, enabling Internet access without injecting Internet routes into the VRF. This feature performs NAT at the VRF-to-global boundary, forwarding traffic from the VRF to the global table while keeping the routing domains separate.

Answer

Static default route from VRF to global

Answer

Route leaking between VRF and global

Answer

VRF-Aware Firewall

Question 9

Refer to the exhibit. Which statement about this BGP configuration is true?

Accepted Answer

The next-hop-self command ensures that the PE sets itself as the next-hop for routes advertised to the route reflector.. The `next-hop-self` command under the VRF address-family instructs the PE router to set its own IP address as the next-hop for routes advertised to the route reflector. This is necessary in MPLS L3VPN environments to ensure that the route reflector (and other PEs) can reach the customer prefix via the advertising PE, avoiding reachability issues when the original next-hop is not directly connected across the MPLS core.

Answer

The no synchronization command is invalid under address-family ipv4 vrf.

Answer

The send-community extended command is only needed for IPv4 unicast address family.

Answer

The redistribute ospf command will import OSPF routes into the VRF but not into BGP.

Question 10

Which TWO features are used to improve BGP convergence in an MPLS VPN environment?

Accepted Answer

Bidirectional Forwarding Detection (BFD). Bidirectional Forwarding Detection (BFD) provides sub-second failure detection for BGP sessions, reducing the time to detect a link or neighbor failure from seconds (default BGP keepalive/hold timers) to milliseconds. BGP Prefix Independent Convergence (PIC) pre-installs backup paths in the forwarding table, allowing traffic to be rerouted immediately upon failure without waiting for BGP to reconverge. Together, these features drastically improve BGP convergence in an MPLS VPN environment.

Answer

Route redistribution

Answer

Next-hop-self

Answer

BGP multipath

Question 11

Which THREE components are required to deploy MPLS Layer 3 VPN?

Accepted Answer

VRFs on PE routers. VRFs (Virtual Routing and Forwarding) are required on PE routers to maintain separate, isolated routing tables for each customer VPN. This allows overlapping IP addresses between different customers and ensures that traffic from one VPN does not leak into another. Without VRFs, the PE router cannot distinguish between customer routes, making Layer 3 VPN operation impossible.

Answer

GRE tunneling

Answer

OSPF

Question 12

Which TWO statements about QoS policy propagation via BGP (QPPB) are correct?

Accepted Answer

QPPB can be applied on inbound direction only.. QPPB can be applied on inbound direction only. QPPB uses BGP policy to classify traffic based on IP precedence or QoS group, and the classification is performed on incoming traffic before any routing decision. The outbound direction is not supported for QPPB classification.

Answer

QPPB is an IETF standard.

Answer

It uses MPLS EXP bits to propagate QoS.

Answer

It dynamically adjusts BGP attributes based on QoS policy.

Question 13

Refer to the exhibit. Which prerequisite for MPLS L3VPN is missing on PE1?

Accepted Answer

VRF is not defined. The exhibit shows that PE1 has an interface configured with an IP address and MPLS enabled, but no VRF definition is present. For MPLS L3VPN, a VRF must be defined on the PE router to separate customer routing tables and to associate the customer-facing interface with that VRF. Without the VRF, the PE cannot import/export VPN routes or maintain per-VPN routing instances, which is a fundamental prerequisite for L3VPN operation.

Answer

MPLS is not enabled on the interface

Answer

LDP is not enabled globally

Answer

OSPF is not redistributed into BGP

Question 14

Refer to the exhibit. Which statement is true regarding the forwarding entry for 10.2.2.0/24?

Accepted Answer

This entry uses explicit label request (not PHP).. The forwarding entry for 10.2.2.0/24 shows an outgoing label of 20, which means the egress LSR is not performing penultimate hop popping (PHP). In MPLS, when the outgoing label is not the implicit-null label (3) or explicit-null label (0), the penultimate hop must push that label, and the egress LSR will perform a full label lookup. This is an explicit label request, not PHP.

Answer

The outgoing interface uses penultimate hop popping.

Answer

The outgoing label is Untagged.

Answer

The local label is 20.

Question 15

A customer is experiencing packet loss during congestion on a link. The service provider wants to implement a QoS policy that drops less important traffic before more important traffic. Which queuing mechanism is best suited?

Accepted Answer

Class-Based Weighted Fair Queuing (CBWFQ) with WRED. CBWFQ with WRED is the best choice because CBWFQ provides per-class queuing with guaranteed bandwidth, while WRED proactively drops less important traffic (based on IP precedence or DSCP) before the queue becomes full, preventing tail drop and ensuring that higher-priority traffic is preserved during congestion. This combination allows the service provider to selectively discard lower-priority packets under congestion, meeting the requirement to drop less important traffic before more important traffic.

Answer

FIFO queuing

Answer

Low Latency Queuing (LLQ)

Answer

Traffic shaping