Select Two (Multi-Select) Questions

GRE tunneling

Why wrong: GRE tunneling is not required; MPLS encapsulation is used.

OSPF

Why wrong: Any IGP (OSPF, IS-IS) can be used; not specifically required.

Distributes labels for BGP routes

Why wrong: LDP does not distribute labels for BGP routes unless specifically configured.

Requires an IGP like OSPF for session reachability

Why wrong: LDP session can be established over any reachable IP, not solely IGP.

TCP for both discovery and session

Why wrong: LDP uses UDP for discovery.

The CE receives a frame with an MPLS label.

Why wrong: CE receives an IP packet without label (unless configured for MPLS).

PHP (Penultimate Hop Popping) causes the egress router to pop the label.

Why wrong: PHP causes the penultimate hop to pop the label, not the egress.

The egress LSR performs label swapping before forwarding.

Why wrong: Egress pops the label, not swap.

Provides inherent security against label spoofing.

Why wrong: SR does not add security features.

Requires BGP-LU for label distribution.

Why wrong: SR uses IGP for label distribution; BGP-LU is optional.

Requires only OSPF as the IGP.

Why wrong: SR works with both OSPF and IS-IS.

Reduces label imposition at the ingress PE.

Why wrong: SR may increase label stack depth.

Faster convergence due to BGP PIC.

Why wrong: BGP PIC is not exclusive to SR; SR uses IGP convergence.

It supports only IS-IS, not OSPF.

Why wrong: Both OSPF and IS-IS are supported.

It carries traffic-engineering parameters in the NLRI.

Why wrong: TE parameters are carried in the BGP-LS attribute, not NLRI.

LDP

Why wrong: LDP distributes labels for LSPs but is not specific to VPNs; it is used for any MPLS forwarding.

VRF

Why wrong: VRF is a configuration element to maintain per-VPN routing tables, but is not a protocol or feature that by itself provides the VPN service.

RSVP-TE

Why wrong: RSVP-TE is used for traffic engineering, not for basic L3VPN operation.

The policy shapes the total output traffic to 30 Mbps.

Why wrong: No shaping command is present; the policy only manages queuing.

Video traffic is placed in a strict priority queue.

Why wrong: Video uses bandwidth remaining percent, not priority.

The policy polices voice traffic to a maximum of 30% of the interface bandwidth.

Why wrong: No police command is configured; the priority queue can consume all available bandwidth.

Model-driven telemetry uses UDP for transport by default.

Why wrong: Typically uses TCP; gRPC or SSL.

Model-driven telemetry only sends data on change (event-driven).

Why wrong: It supports both periodic and on-change; not only on-change.

Model-driven telemetry uses MIBs to define data structures.

Why wrong: MIBs are SNMP; telemetry uses YANG.

conform action is drop

Why wrong: Conform action is normally transmit, not drop.

no bandwidth is reserved

Why wrong: Bandwidth reservation is for scheduling, not policing.

queue is full

Why wrong: Queue fullness causes tail drop, not policing.

WRED

Why wrong: WRED is congestion avoidance, not policing.

shaping

Why wrong: Shaping buffers traffic, not policing.

Configure no bgp default community-mode

Why wrong: Incorrect. This is not a valid Cisco command.

Configure vrf forwarding with route-target both

Why wrong: Incorrect. Route-target is for MPLS VPN route import/export, not for community propagation.

Configure route-map to filter communities

Why wrong: Incorrect. A route-map is optional for filtering, not necessary for propagation.

Shortest AS_PATH

Why wrong: AS_PATH length is considered after metric (step 6), not before.

Lowest origin type (IGP < EGP < incomplete)

Why wrong: Origin is considered after metric (step 7), not before.

OSPF uses the Bellman-Ford algorithm to compute routes.

Why wrong: OSPF uses Dijkstra's SPF algorithm.

OSPF is a distance-vector routing protocol.

Why wrong: OSPF is a link-state routing protocol.

OSPF uses TLVs to encode routing information.

Why wrong: TLVs are used by IS-IS, not OSPF.

Verify that TCP port 646 is open on the interface ACL.

Why wrong: LDP uses UDP for discovery and TCP for session; but the question asks for verification steps, and this is too specific; not the first step.

Verify that 'mpls ip' is enabled globally.

Why wrong: The 'mpls ip' command is not needed; 'mpls ldp' under interface is sufficient.

Verify that OSPF is configured on the interface.

Why wrong: LDP does not require OSPF; any IGP works.

FlowSpec uses a separate BGP session from the regular IPv4 unicast session.

Why wrong: FlowSpec can be carried in the same session using additional address families.

FlowSpec is designed to replace ACLs on provider edge routers.

Why wrong: FlowSpec provides dynamic traffic filtering but does not replace static ACLs entirely.

FlowSpec requires MPLS forwarding to operate.

Why wrong: FlowSpec can operate on pure IP networks.

VPLS requires all PE routers to be in the same VLAN.

Why wrong: VPLS uses bridge domains, not necessarily the same VLAN.

VPLS uses a hub-and-spoke topology to interconnect multiple sites.

Why wrong: VPLS uses a full-mesh of pseudowires.

EoMPLS supports MAC address learning between sites.

Why wrong: EoMPLS does not perform MAC learning.

Policing

Why wrong: Policing is a traffic conditioning mechanism, not congestion avoidance.

CBWFQ

Why wrong: CBWFQ is a queuing mechanism.

LLQ

Why wrong: LLQ is a queuing mechanism that provides strict priority.

QoS policies cannot be applied to MPLS interfaces due to label encapsulation.

Why wrong: QoS policies can be applied to MPLS interfaces, often using EXP-based classification.

802.1p CoS marking is preserved across the MPLS backbone by default.

Why wrong: 802.1p is typically not preserved across MPLS backbone without explicit mapping.