350-501 Practice Test 47 — 15 Questions

Question 1

Which TWO conditions cause a router to drop packets when a police action is configured?

Accepted Answer

exceed action is drop. When a police action is configured, the router uses a token bucket model to meter traffic. If traffic exceeds the committed information rate (CIR) and burst size, it falls into the 'exceed' or 'violate' category depending on the configured conform and exceed burst parameters. The 'drop' action for exceed or violate conditions explicitly instructs the router to discard those packets, enforcing traffic shaping or policing at the hardware or software level.

Answer

conform action is drop

Answer

no bandwidth is reserved

Answer

queue is full

Question 2

Refer to the exhibit. What is the significance of the entry with 'Pop Label'?

Accepted Answer

It indicates the penultimate hop popping (PHP). In MPLS, the 'Pop Label' entry in a forwarding table indicates the Penultimate Hop Popping (PHP) operation. PHP is a standard behavior (RFC 3031) where the penultimate router removes the MPLS label before forwarding the packet to the egress LSR, reducing the egress router's processing load. This is explicitly signaled via the 'implicit-null' label (label value 3) in LDP or RSVP-TE.

Answer

It indicates a merge operation

Answer

It indicates the label is removed at this router

Answer

It indicates an error

Question 3

Refer to the exhibit. An engineer is troubleshooting an MPLS LDP session between two routers. The output shows that the LDP session is operational. However, MPLS labels are not being exchanged. What is the most likely cause?

Accepted Answer

The LDP label advertisement mode is 'downstream on demand'.. The exhibit shows that the LDP session is operational (state = Operational), but no labels are being exchanged. In 'downstream on demand' mode, a router does not advertise labels unless explicitly requested by an upstream neighbor via a Label Request message. Since the session is up but no labels are exchanged, this mismatch in label advertisement mode is the most likely cause.

Answer

The peer's addresses are not bound to the LDP Ident.

Answer

The TCP connection is not using port 646.

Answer

The LDP session is not established.

Question 4

When implementing MPLS TE tunnels in a service provider core, what is the purpose of the 'affinity' attribute?

Accepted Answer

To define administrative groups for link inclusion/exclusion. The 'affinity' attribute in MPLS TE is used to define administrative groups (also known as link colors) that allow you to include or exclude specific links from a TE tunnel path based on user-defined properties. This enables traffic engineering policies such as forcing traffic to avoid certain links or preferring links with specific characteristics, without modifying the underlying IGP metric.

Answer

To set the color of the tunnel

Answer

To adjust the cost of TE tunnels

Answer

To bind tunnels to specific interfaces

Question 5

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 6

An MPLS network is experiencing micro-loops during convergence after a link failure. The network uses LDP and IS-IS as IGP. Which of the following solutions can prevent micro-loops during IGP convergence without requiring additional protocols?

Accepted Answer

Configure LFA (Loop-Free Alternate) on the IGP.. LFA (Loop-Free Alternate) is a feature built directly into IGPs like IS-IS and OSPF that precomputes a backup next-hop that does not loop back to the failed link. This prevents micro-loops during IGP convergence without requiring any additional protocols such as RSVP-TE or BGP, making it a lightweight, protocol-integrated solution.

Answer

Implement MPLS-TE FRR using bypass tunnels.

Answer

Enable BGP PIC (Prefix Independent Convergence).

Answer

Deploy RSVP-TE with fast-reroute.

Question 7

A service provider is implementing MPLS L3VPN for a customer. The customer requires that routes from two different VPNs be imported into a single VRF. Which feature should be used?

Accepted Answer

Route Target (RT) import/export. Route Target (RT) import/export is the correct feature because it controls which routes from which VPNs are imported into a given VRF. By configuring multiple RT import statements on a single VRF, the provider can selectively import routes from two different VPNs, enabling inter-VPN route sharing without merging the VPNs themselves.

Answer

Route Reflector

Answer

Route Distinguisher (RD)

Answer

BGP extended community

Question 8

A network engineer notices that BGP-LU prefixes learned from an eBGP neighbor are not being installed in the MPLS forwarding table (LFIB). The BGP table shows the prefixes with the correct label. The IGP route to the neighbor is reachable. What additional configuration is needed?

Accepted Answer

Set `label mode per-prefix` under the BGP neighbor or address-family. BGP-LU (BGP Labeled Unicast) installs labels into the BGP table, but for those labels to be used for MPLS forwarding, the router must be configured to allocate labels on a per-prefix basis. By default, BGP may use per-VRF or per-next-hop label allocation, which does not populate the LFIB with per-prefix entries. Setting `label mode per-prefix` under the BGP neighbor or address-family forces BGP to allocate a unique label for each prefix, enabling the LFIB installation required for MPLS forwarding.

Answer

Enable `no bgp default ipv4-unicast`

Answer

Configure `mpls ldp autoconfig` on the interface

Answer

Add `allowas-in` to accept routes with AS-path containing own AS

Question 9

A network architect is designing an MPLS network that must provide fast convergence in case of a link failure. The network uses Segment Routing. Which mechanism provides sub-50ms protection by using a precomputed backup path?

Accepted Answer

TI-LFA (Topology-Independent Loop-Free Alternate). B is correct because TI-LFA (Topology-Independent Loop-Free Alternate) is a Segment Routing mechanism that precomputes a backup path using a segment list, enabling sub-50ms convergence upon link failure. It guarantees loop-free forwarding even in complex topologies where traditional LFA may fail, by leveraging SR's source routing capabilities.

Answer

BFD (Bidirectional Forwarding Detection)

Answer

LFA (Loop-Free Alternate)

Answer

LDP FRR

Question 10

A service provider is implementing 6VPE to provide IPv6 L3VPN services over an MPLS core. Which BGP address family must be configured on the PE routers to exchange IPv6 VPN routes?

Accepted Answer

VPNv6 unicast. 6VPE uses the VPNv6 address family (or IPv6 labeled unicast with VPN extensions) to carry IPv6 prefixes with VPN-IPv6 addresses.

Answer

IPv6 unicast

Answer

VPNv4 unicast

Answer

IPv4 unicast

Question 11

An engineer is configuring IS-IS in a service provider network. The network uses wide metrics for traffic engineering. Which TLV is mandatory for IS-IS to carry traffic engineering (TE) information in accordance with RFC 5305?

Accepted Answer

TLV 22 (Extended IS Reachability). TLV 22 (Extended IS Reachability) is the mandatory TLV for IS-IS TE, defined in RFC 5305.

Answer

TLV 135 (Extended IP Reachability)

Answer

TLV 229 (Multi-Topology Reachable IPv4 Prefixes)

Answer

TLV 128 (IP Internal Reachability)

Question 12

An SP is designing an OSPF network with a totally stubby area to reduce the LSA database. Which LSA types are blocked by default in a totally stubby area?

Accepted Answer

Type 3, Type 4, and Type 5. Totally stubby area blocks Type 4 (ASBR Summary) and Type 5 (External) LSAs, and also Type 3 (Summary) LSAs except for the default route.

Answer

Type 3 and Type 5 only

Answer

Type 5 only

Answer

Type 4 and Type 5 only

Question 13

Which BGP attribute is locally significant and used to influence outbound traffic from an AS?

Accepted Answer

LOCAL_PREF. LOCAL_PREF is used to influence the path selection for outbound traffic within the AS, with higher preference preferred.

Answer

WEIGHT

Answer

AS_PATH

Answer

MED

Question 14

An SP network engineer configures IS-IS with wide metrics. Which statement is true about IS-IS wide metrics compared to narrow metrics?

Accepted Answer

Wide metrics use Type-Length-Value (TLV) extensions to carry traffic engineering information.. Wide metrics use a 24-bit field, allowing values up to 16,777,215, and support TE extensions and segment routing.

Answer

Narrow metrics are required for IPv6 routing in IS-IS.

Answer

Wide metrics are only supported in Level 1 routing.

Answer

Narrow metrics support up to 63 cost values, while wide metrics support up to 255.

Question 15

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