Sample Questions and Answers
What type of BGP route target community is typically assigned to a VRF to import routes?
A) Route Target Import
B) Route Target Export
C) Route Distinguisher
D) Standard Community
Answer: A) Route Target Import
Explanation: Import RT defines which routes a VRF will accept from other VPNs.
Which MPLS label stack entry is the bottom of stack (BOS) label?
A) The last label in the stack marked with BOS bit set to 1
B) The first label in the stack marked with BOS bit set to 1
C) Label 0
D) Label 3
Answer: A) The last label in the stack marked with BOS bit set to 1
Explanation: The BOS bit indicates that this label is the last one in the MPLS stack.
In MPLS VPNs, which routing protocol is most commonly used between CE and PE routers?
A) OSPF, EIGRP, or BGP (depending on customer requirements)
B) Only BGP
C) Only static routing
D) ISIS exclusively
Answer: A) OSPF, EIGRP, or BGP (depending on customer requirements)
Explanation: Various protocols can be used depending on the customer’s and provider’s configuration.
What is the purpose of the neighbor route-reflector-client command in BGP?
A) To designate a neighbor as a route reflector client, reducing peering overhead
B) To enable VPN route advertisement
C) To configure BGP authentication
D) To enable LDP on the neighbor interface
Answer: A) To designate a neighbor as a route reflector client, reducing peering overhead
Explanation: Route reflectors reduce the need for full mesh BGP peering.
Which of the following MPLS VPN components is responsible for forwarding labeled packets through the provider core?
A) Provider (P) router
B) Provider Edge (PE) router
C) Customer Edge (CE) router
D) Route reflector
Answer: A) Provider (P) router
Explanation: P routers switch MPLS labeled packets but do not maintain VPN routes.
How does a PE router identify packets belonging to a specific VRF when receiving them from a CE?
A) By the interface associated with the VRF or by VLAN tags in Layer 2 VPNs
B) By inspecting the MPLS label stack only
C) By MAC address
D) By the next-hop IP address
Answer: A) By the interface associated with the VRF or by VLAN tags in Layer 2 VPNs
Explanation: PE router uses interface-to-VRF binding to associate incoming packets with a VRF.
What MPLS VPN feature allows a provider to offer overlapping IP address spaces for different customers?
A) VRF (Virtual Routing and Forwarding)
B) LDP
C) RSVP-TE
D) Route reflector
Answer: A) VRF (Virtual Routing and Forwarding)
Explanation: VRFs isolate routing tables per customer, allowing overlapping IP spaces.
What does the mpls label protocol ldp command configure on a Cisco router?
A) Enables LDP as the label distribution protocol
B) Enables RSVP as the label distribution protocol
C) Disables MPLS labeling
D) Configures static label assignments
Answer: A) Enables LDP as the label distribution protocol
Explanation: This command configures LDP for label distribution.
Which command displays the active VRFs on a Cisco router?
A) show ip vrf
B) show mpls ldp bindings
C) show bgp vpnv4
D) show ip route
Answer: A) show ip vrf
Explanation: Displays the list of VRFs configured on the router.
What is the main benefit of using MPLS TE (Traffic Engineering) in a service provider network?
A) Efficient bandwidth utilization and optimized traffic paths
B) Automatic encryption of customer data
C) Simplification of customer IP address planning
D) Reducing MPLS label stack depth
Answer: A) Efficient bandwidth utilization and optimized traffic paths
Explanation: MPLS TE allows explicit path setup and traffic load balancing.
What type of VPN service does L2TPv3 provide over an MPLS core?
A) Layer 2 VPN
B) Layer 3 VPN
C) Internet VPN
D) Remote access VPN
Answer: A) Layer 2 VPN
Explanation: L2TPv3 encapsulates Layer 2 frames over MPLS networks.
Which MPLS VPN design allows multiple VRFs to share a common CE router?
A) Hub-and-spoke VRF design with VRF leaking
B) Full mesh CE design
C) Single VRF per CE design
D) Static routing only
Answer: A) Hub-and-spoke VRF design with VRF leaking
Explanation: VRF leaking allows route sharing between multiple VRFs.
In MPLS VPNs, what is the function of the ip vrf route-target import command?
A) Specifies the Route Targets that define which routes a VRF will import
B) Defines the route target to export routes from the VRF
C) Assigns a Route Distinguisher to the VRF
D) Enables MPLS on the interface
Answer: A) Specifies the Route Targets that define which routes a VRF will import
Explanation: Import RT controls what routes the VRF accepts.
Which MPLS VPN feature ensures that VPN routes are kept separate in BGP?
A) Route Distinguisher (RD)
B) Route Target (RT)
C) Local Preference
D) MED
Answer: A) Route Distinguisher (RD)
Explanation: RD makes prefixes unique by prepending an identifier.
What does the show mpls forwarding-table command display?
A) MPLS label forwarding entries and their outgoing interfaces
B) BGP VPNv4 routes
C) VRF configurations
D) IP routing table
Answer: A) MPLS label forwarding entries and their outgoing interfaces
Explanation: Shows label-to-interface mappings for MPLS forwarding.
Which protocol does a Cisco PE router commonly use to distribute VPN routes?
A) MP-BGP
B) OSPF
C) RIP
D) EIGRP
Answer: A) MP-BGP
Explanation: MP-BGP extends BGP to support VPN route exchange.
In MPLS, what is the term for the initial label imposed by the ingress PE router?
A) Outer label
B) Inner label
C) Top label
D) Bottom label
Answer: A) Outer label
Explanation: The ingress PE imposes an outer label used by the provider core.
What is the command to associate an interface with a VRF?
A) ip vrf forwarding <vrf-name>
B) mpls ip
C) router bgp
D) interface vrf <vrf-name>
Answer: A) ip vrf forwarding <vrf-name>
Explanation: This binds an interface to the specified VRF.
What is the purpose of MPLS Label Stacking?
A) To support multiple layers of forwarding information for services like VPNs and QoS
B) To provide encryption for data packets
C) To reduce packet size
D) To perform route summarization
Answer: A) To support multiple layers of forwarding information for services like VPNs and QoS
Explanation: Labels are stacked to enable hierarchical forwarding decisions.
Which router type in an MPLS VPN core only forwards MPLS labeled packets and does not maintain VRFs?
A) Provider (P) router
B) Provider Edge (PE) router
C) Customer Edge (CE) router
D) Route reflector
Answer: A) Provider (P) router
Explanation: P routers only switch labels and do not maintain VPN state.
Which of the following BGP attributes is used to influence route preference outside the AS?
A) Multi-Exit Discriminator (MED)
B) Local Preference
C) Origin
D) Next-Hop
Answer: A) Multi-Exit Discriminator (MED)
Explanation: MED is used to influence inbound traffic from neighboring ASes.
What does the mpls ip command do when applied to an interface?
A) Enables MPLS forwarding on the interface
B) Enables IP routing on the interface
C) Disables MPLS on the interface
D) Configures the interface as a loopback
Answer: A) Enables MPLS forwarding on the interface
Explanation: It activates MPLS label switching for that interface.
In an MPLS Layer 3 VPN, which component handles VRF import/export policies?
A) Route Targets
B) Route Distinguisher
C) MPLS labels
D) Route reflector
Answer: A) Route Targets
Explanation: RTs control route sharing between VRFs.
Which of the following is NOT a valid VRF route target format?
A) ASN:NN
B) IP-address:NN
C) 32-bit integer only
D) Extended community
Answer: C) 32-bit integer only
Explanation: RTs are extended BGP communities, not plain integers.
What MPLS label is used to indicate Explicit Null?
A) 0
B) 3
C) 1
D) 255
Answer: A) 0
Explanation: Label 0 (Explicit Null) indicates to forward the packet with the IP header intact.
In MPLS VPNs, what is the purpose of the BGP Next-Hop attribute?
A) It indicates the IP address to be used as the next-hop for the VPN route
B) It carries the MPLS label value
C) It defines the route distinguisher
D) It sets the local preference
Answer: A) It indicates the IP address to be used as the next-hop for the VPN route
Explanation: PE routers use the next-hop attribute to forward packets.
Which feature enables a PE router to advertise customer routes to other PEs?
A) MP-BGP VPNv4 address family
B) OSPF redistribution
C) Static routing
D) LDP
Answer: A) MP-BGP VPNv4 address family
Explanation: MP-BGP carries VPN routes between PEs.
How are VRF interfaces identified in the routing table?
A) By their unique Route Distinguisher (RD)
B) By their MAC address
C) By their physical interface name
D) By their IP address only
Answer: A) By their unique Route Distinguisher (RD)
Explanation: RD ensures uniqueness across overlapping address spaces.
What is the role of a CE router in an MPLS VPN?
A) Connects the customer network to the provider network
B) Performs MPLS label switching in the core
C) Maintains VRFs
D) Reflects routes within the provider AS
Answer: A) Connects the customer network to the provider network
Explanation: CE routers interface between customer and provider networks.
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