350-501 Practice Test 9 — 10 Questions

Question 1

An engineer is troubleshooting MPLS LSP connectivity. The ingress PE router has the label binding for the FEC 10.1.1.0/24, but no LSP is established. Which command should be checked on the P routers to verify the LSP path?

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

Accepted Answer

show mpls forwarding-table. The correct command is 'show mpls forwarding-table' because it displays the LFIB (Label Forwarding Information Base) on each P router. Since the ingress PE has a label binding for FEC 10.1.1.0/24 but no LSP is established, the issue likely lies in label propagation or forwarding along the path. Checking the LFIB on P routers reveals whether they have installed the correct outgoing label and interface for that FEC, which is essential for LSP connectivity.

Answer

show mpls interface

Answer

show mpls ldp neighbor

Answer

show ip route 10.1.1.0

Question 2

Which THREE of the following are required components for implementing MPLS Layer 3 VPN (L3VPN) in a service provider network? (Choose three.)

Accepted Answer

MP-BGP between PE routers to exchange VPNv4 routes. MP-BGP (Multiprotocol BGP) is essential for carrying VPNv4 routes between PE routers. It uses address family VPNv4 to transport customer IPv4 prefixes along with their Route Distinguisher (RD) and Route Target (RT) attributes, enabling the separation and distribution of multiple customer VPNs across the MPLS core.

Answer

IBGP between PE and P routers for label distribution

Answer

VRF configuration on P routers

Question 3

A network operator is implementing segment routing (SR-MPLS) using OSPF as the IGP. Which OSPF TLV is used to advertise the Node SID (Prefix SID) for a router's loopback address?

Accepted Answer

Extended Prefix TLV. In OSPF, the Extended Prefix TLV (type 1) carries the Prefix SID sub-TLV for segment routing. The Adjacency SID is carried in the Extended Link TLV.

Answer

Router Information TLV

Answer

Traffic Engineering TLV

Answer

Extended Link TLV

Question 4

Refer to the exhibit. The VRF CUSTOMER is configured with route-target import 100:1. Why is this route not installed in the VRF table?

Accepted Answer

Route target mismatch.. B is correct because the VRF CUSTOMER is configured with route-target import 100:1, but the route in question carries a different route-target value (e.g., 100:2). For a route to be installed into a VRF table, the route-target extended community attached to the route must match at least one of the import route-targets configured on the VRF. A mismatch prevents the route from being imported, even if other conditions are satisfied.

Answer

VRF not properly configured.

Answer

Route distinguisher missing.

Answer

Next-hop unreachable.

Question 5

A service provider wants to mitigate DDoS attacks by blackholing traffic destined to a victim IP address. They plan to use Remotely Triggered Black Hole (RTBH) filtering. What BGP community is commonly used to trigger the blackhole route?

Accepted Answer

Community 666. RTBH works by advertising a /32 route with a specific community (often 666 or a locally defined one) that causes the router to forward traffic to a null interface. The well-known community for RTBH is often 666 or custom.

Answer

Community 100

Answer

Community no-export

Answer

Community local-AS

Question 6

Which LDP mode uses downstream unsolicited label distribution and liberal label retention?

Accepted Answer

Downstream unsolicited with liberal retention. Downstream unsolicited (DU) label distribution is the default mode in LDP, where each LSR advertises labels for all its directly connected prefixes to its neighbors without waiting for a request. Liberal label retention means the LSR stores all received label bindings, even if they are not currently used for forwarding, which enables rapid convergence upon topology changes.

Answer

Downstream on demand with liberal retention

Answer

Upstream unsolicited with liberal retention

Answer

Downstream on demand with conservative retention

Question 7

An engineer wants to configure SR-TE without using RSVP. Which mechanism does SR-TE use to specify the explicit path?

Accepted Answer

Segment list in SR Policy. SR-TE uses a segment list consisting of Node SIDs and/or Adjacency SIDs to define the explicit path, avoiding RSVP state.

Answer

ERO in RSVP PATH message

Answer

Label stack with PHP

Answer

IGP shortest path only

Question 8

Which label operation is performed on a router when an MPLS packet arrives with a top label that matches a local label assigned to a directly connected prefix?

Accepted Answer

Pop. If the top label corresponds to a directly connected prefix, the router will pop the label (penultimate hop popping or explicit null) and forward the packet based on the inner header.

Answer

No operation, label is ignored

Answer

Push

Answer

Swap

Question 9

An engineer is configuring RSVP-TE fast reroute for link protection. Which protection method uses a pre-configured bypass tunnel that protects multiple LSPs on the same link?

Accepted Answer

Facility backup. In RSVP-TE FRR, facility backup uses a bypass tunnel that can protect multiple LSPs on the same link. In contrast, 1:1 detour creates a separate detour LSP for each protected LSP.

Answer

Local Path Protection

Answer

Global Repair

Answer

1:1 detour

Question 10

Which LDP label distribution mode is characterized by a router advertising labels for all prefixes in its routing table to all neighbors, regardless of whether they are needed?

Accepted Answer

Downstream unsolicited with liberal label retention. Downstream unsolicited means the router sends label bindings without being asked; liberal label retention means it keeps all bindings even if not from the next hop.

Answer

Downstream on demand with conservative label retention

Answer

Downstream on demand with liberal label retention

Answer

Downstream unsolicited with conservative label retention