350-501 Practice Test 8 — 10 Questions

Question 1

A service provider is implementing MPLS TE to optimize bandwidth utilization. The engineer notices that tunnels are not using the explicitly configured path. What is the most likely reason?

Accepted Answer

The explicit path contains a link that is down. When an MPLS TE tunnel is configured with an explicit path, the headend router uses RSVP to signal the path and verify that all links in the path are operational. If any link in the explicit path is down, RSVP signaling fails for that path, and the tunnel may fall back to dynamic path computation or remain down, rather than using the explicitly configured path. This is the most common reason for a tunnel not using its explicit path.

Answer

RSVP is not enabled on the headend

Answer

The tunnel destination is not reachable via IGP

Answer

The tunnel is configured with 'autoroute announce'

Question 2

In EVPN-VPWS, which component is used to identify a multi-homed Ethernet segment and enable load balancing and fast convergence?

Accepted Answer

Ethernet Segment Identifier (ESI). The Ethernet Segment Identifier (ESI) is a unique identifier for an Ethernet segment that is multi-homed to two or more PEs. ESI is used for DF election and aliasing.

Answer

Ethernet Tag ID

Answer

MAC address

Answer

EVPN Route Target

Question 3

An enterprise uses IPsec VPN to connect branch offices. They apply QoS policies on the tunnel interface but notice that original DSCP markings are not preserved after encryption. Which feature should be enabled to maintain end-to-end QoS?

Accepted Answer

QoS pre-classify. When IPsec encrypts a packet, the original IP header (including DSCP markings) is hidden inside the tunnel payload. The tunnel interface then applies a new outer IP header, and QoS policies applied to the tunnel interface classify based on the outer header's DSCP, which defaults to 0. Enabling 'qos pre-classify' on the crypto map or tunnel interface copies the original DSCP value to the outer IP header before encryption, preserving end-to-end QoS markings across the IPsec tunnel.

Answer

AutoQoS

Answer

MPLS TE

Answer

NBAR

Question 4

Refer to the exhibit. The router has an outgoing label of 'Pop' for prefix ***********. What does this imply?

Accepted Answer

The router is the penultimate hop and will remove the label before forwarding. When a router has an outgoing label of 'Pop' for a prefix in MPLS, it indicates that the router is the penultimate hop (PHP) in the LSP. PHP means the router will remove (pop) the top label before forwarding the packet to the next hop, reducing the burden on the egress LSR. This is standard MPLS behavior as per RFC 3031, where the egress router signals an implicit null label (label 3) to its upstream neighbor.

Answer

The router has not learned a label for that prefix

Answer

The router will not forward traffic for that prefix

Answer

The router will push a new label for that prefix

Question 5

A service provider is implementing QoS policies on an access aggregation router. They want to shape traffic to a downstream DSLAM to 10 Mbps, but they do not want to exceed the shaping rate even if the line rate is higher. Which QoS tool should be used on the interface facing the DSLAM?

Accepted Answer

Shaping. Shaping is the correct tool because it buffers excess traffic and smooths the output rate to a configured target (10 Mbps) without exceeding it, even if the physical line rate is higher. Unlike policing, shaping does not drop or re-mark packets when the rate is exceeded, ensuring the downstream DSLAM receives traffic at or below the shaped rate.

Answer

Queuing

Answer

Marking

Answer

Policing

Question 6

In EVPN multi-homing, which two mechanisms are used to avoid duplicate packets and ensure efficient forwarding? (Choose two.)

Accepted Answer

Split-horizon filtering. Designated Forwarder (DF) election ensures only one PE forwards traffic to the CE for broadcast/multicast/unknown unicast, and split-horizon prevents a PE from forwarding packets back to the ES from which they were received.

Answer

MAC mobility

Answer

Aliasing

Answer

ARP suppression

Question 7

In IS-IS, which TWO are types of Link State PDUs (LSPs)?

Accepted Answer

Level 2 LSP. In IS-IS, Link State PDUs (LSPs) are the fundamental building blocks of the link-state database. They carry topology and prefix information and are generated by each router. There are two distinct types: Level 1 LSPs, which advertise information within the same area, and Level 2 LSPs, which advertise information between areas. Options B and E correctly identify these two types.

Answer

Partial Sequence Numbers PDU (PSNP)

Answer

Hello LSP

Answer

Complete Sequence Numbers PDU (CSNP)

Question 8

Which TWO statements correctly describe the use of OSPF in a service provider network?

Accepted Answer

OSPF uses different LSA types to advertise different types of routing information.. OSPF uses different LSA types (e.g., Type 1 Router LSA, Type 2 Network LSA, Type 3 Summary LSA, Type 5 AS-External LSA) to advertise different categories of routing information, such as router links, network links, inter-area routes, and external routes. This LSA-type differentiation is fundamental to OSPF's link-state architecture, enabling efficient flooding and route computation within and across areas.

Answer

OSPF uses the Bellman-Ford algorithm to compute routes.

Answer

OSPF is a distance-vector routing protocol.

Answer

OSPF uses TLVs to encode routing information.

Question 9

In a carrier-supporting carrier (CSC) architecture, the customer carrier runs MPLS in its network. Which technology is used to exchange VPN routes between the provider carrier and the customer carrier?

Accepted Answer

MP-BGP with VPNv4 address family. In a carrier-supporting-carrier (CSC) architecture, the customer carrier runs MPLS in its network and needs to exchange VPN routes (e.g., customer VPN prefixes) with the provider carrier. MP-BGP with the VPNv4 address family is the correct technology because it carries both the IPv4 prefix and the Route Distinguisher (RD), enabling the provider carrier to distinguish overlapping VPN routes from different customer VPNs. This is defined in RFC 4364 and is the standard inter-AS VPN option for CSC scenarios.

Answer

OSPF

Answer

EIGRP

Answer

IPv4 BGP

Question 10

Which THREE of the following are key components of an MPLS L3VPN architecture? (Choose three.)

Accepted Answer

VRF on PE routers. VRF (Virtual Routing and Forwarding) on PE routers is a key component because it isolates customer routing tables and forwarding planes within the provider edge, allowing multiple customers to share the same physical infrastructure while maintaining separate routing domains. Each VRF maintains its own routing table, CEF (Cisco Express Forwarding) table, and associated interfaces, which is fundamental to L3VPN separation.

Answer

RSVP-TE for traffic engineering

Answer

P routers with full VPN routing tables