nokia 4A0-100 Exam Questions
Questions for the 4A0-100 were updated on : Nov 21 ,2025
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Question 1
Which of the MPLS routers is responsible for pushing new labels for LSP A and LSP B?
- A. Router R1 pushes labels for both LSP A and LSP B.
- B. Router R4 pushes labels for both LSP A and LSP B.
- C. Router R1 pushes labels for LSP A, while router R4 pushes labels for LSP B.
- D. Router R4 pushes labels for LSP A, while router R1 pushes labels for LSP B.
Answer:
C
Explanation:
Reference:
Nokia MPLS Fundamentals Guide – Chapter: “Label Operations (Push, Swap, Pop)”
Nokia SRA Study Guide – Ingress/Egress LER roles in MPLS
Question 2
Which of the following statements about VPLS is FALSE?
- A. A VPLS emulates a virtual switch or bridge.
- B. A VPLS learns source MAC addresses from SAPs and SDPs.
- C. A VPLS discards frames with unknown MAC destinations.
- D. A MAC address forwarding database (FDB) is maintained for each VPLS.
Answer:
C
Explanation:
VPLS (Virtual Private LAN Service) is a Layer 2 VPN service that emulates a bridged Ethernet LAN
across an MPLS/IP network.
Learns MAC addresses dynamically from:
SAPs (Service Access Points)
SDPs (Service Distribution Points)
Maintains a Forwarding Database (FDB) per VPLS instance.
For unknown MAC destinations, a VPLS floods the frame to all other sites – just like a regular
Ethernet switch.
Option C is FALSE – VPLS does NOT discard unknown MACs; it floods them.
Reference:
Nokia VPLS Services Guide – Learning and Forwarding
Nokia SRA Study Guide – VPLS Operation
Question 3
In an MPLS network, which device is responsible for taking an unlabeled packet and encapsulating it
with an MPLS label?
- A. Ingress Label Edge Router
- B. Egress Label Edge Router
- C. Label Switching Router
- D. Next-hop Router
Answer:
A
Explanation:
The Ingress Label Edge Router (LER) is the first router that:
Receives an unlabeled IP packet.
Applies an MPLS label based on its forwarding decision.
Forwards it into the MPLS core.
Option A is correct – Ingress LER does MPLS label push.
Option B (Egress LER) – removes labels at the end of the path.
Option C (LSR) – switches labels, but doesn’t push them onto unlabeled packets.
Option D – is not a specific MPLS role.
Reference:
Nokia IP/MPLS Fundamentals Guide – Label Operations
RFC 3031 – MPLS Architecture
Question 4
Where would you expect to find a P router in a service provider's network?
- A. At the edge of the provider's network facing the customer.
- B. At the edge of the customer's network facing the provider.
- C. In the core of the provider's network.
- D. On the customer premises.
Answer:
C
Explanation:
A P router (Provider router) is located in the core of the service provider’s network. Its functions
include:
Forwarding MPLS-labeled packets between PE routers.
Not interacting directly with customer routes or routing instances.
Having no knowledge of VPN routing or customer-specific services.
Option C is correct – P routers sit in the MPLS core, isolated from customer edge.
Reference:
Nokia MPLS and Services Guide – Core vs Edge Router Roles
Nokia SRA Study Guide – "PE and P Devices in MPLS"
Question 5
Which of the following devices connects directly to the customer equipment?
- A. PE
- B. P
- C. LSR
- D. Both P and LSR
Answer:
A
Explanation:
In a typical MPLS/VPN service architecture:
PE (Provider Edge) router: Directly connects to the customer edge (CE) device.
P (Provider) router: Only forwards MPLS-labeled packets, does not touch customer routes.
LSR (Label Switch Router): General term, can be either PE or P depending on placement.
Correct Answer: A – PE
Explanation:
It interfaces with CE devices and runs customer routing protocols (e.g., OSPF, BGP).
Reference:
Nokia MPLS and VPN Guide – PE vs P Role
Nokia SRA Study Guide – PE-CE and Core Router Design
Question 6
From a customer's perspective, how does a VPRN service operate?
- A. All sites are connected to a single wire.
- B. All sites are connected to a switched network.
- C. All sites are connected to a routed network.
- D. All sites are connected to the Internet.
Answer:
C
Explanation:
A VPRN (Virtual Private Routed Network) provides a Layer 3 VPN service over a service provider’s
network.
Each customer site connects to a PE router.
Sites are connected via a routed network using separate routing instances.
Customer routers see routed connectivity, as if connected to their own private WAN.
Option C is correct – VPRN provides routed connectivity between sites.
Reference:
Nokia Service Routing Guide – Chapter: VPRN
Nokia SRA Guide – Service Types and Operation
Question 7
Which of the following statements about the VPWS service on a Nokia 7750 SR is FALSE?
- A. VPWS is a point-to-point service.
- B. VPWS emulates a layer-2 connection between two customer sites.
- C. VPWS does not perform MAC learning.
- D. VPWS encapsulates layer-2 frames into IP datagrams.
Answer:
D
Explanation:
VPWS (Virtual Private Wire Service) on Nokia 7750 SR:
Emulates a Layer 2 point-to-point connection.
Does not require MAC learning, unlike VPLS.
Uses MPLS encapsulation, not IP datagrams for transport.
Option D is FALSE – VPWS uses MPLS labels, not IP encapsulation.
Reference:
Nokia 7750 SR Service Router Guide – VPWS Overview
Nokia SRA Study Guide – Chapter: Layer 2 Services
Question 8
Which tier of Internet service providers provides transit services to other ISPs?
- A. Tier 1 and Tier 2 ISPs
- B. Tier 1 and Tier 3 ISPs
- C. Tier 2 and Tier 3 ISPs
- D. Tier 3 ISP
Answer:
A
Explanation:
Tier 1 ISPs: Have global reachability and exchange traffic via peering. They do not pay for transit.
Tier 2 ISPs: Purchase transit services from Tier 1 and provide transit to Tier 3 or other Tier 2 ISPs.
Tier 3 ISPs: Provide last-mile connectivity to end users and do not provide transit services.
Option A is correct – Tier 1 and Tier 2 provide transit services.
Reference:
Nokia IP Networks and Services Guide – ISP Tiering
Global Internet Infrastructure Overview
Question 9
Which of the following statements best describes BGP route selection?
- A. It uses SPF algorithm to calculate the shortest paths.
- B. It uses link metrics to calculate the shortest paths.
- C. It uses multiple criteria to choose the best routes.
- D. It uses the preference value to choose the best routes.
Answer:
C
Explanation:
BGP (Border Gateway Protocol) uses a multi-step decision process to select the best route among
multiple paths. It does not use SPF or simple metrics like hop count.
Key BGP selection criteria include:
Local preference
AS path length
Origin type
MED (Multi-Exit Discriminator)
eBGP over iBGP
IGP metric to next hop
Option C is correct – BGP evaluates multiple attributes for route selection.
Reference:
Nokia IP Routing Fundamentals – BGP Route Selection
RFC 4271 – BGP Decision Process
Question 10
Which of the following routing protocols cannot be used between routers R2 and R4?
- A. Static Routing
- B. IS-IS
- C. OSPF
- D. eBGP
Answer:
D
Explanation:
In the diagram:
R2 and R4 are both within AS 65540, which indicates that they are in the same Autonomous System.
eBGP (External Border Gateway Protocol) is designed for routing between different ASes (inter-AS
routing).
Since R2 and R4 are in the same AS, you would use:
OSPF or IS-IS (both interior gateway protocols – IGPs)
✔
Static routing is also valid between any two routers if manually configured
✔
❌
eBGP
is invalid between routers in the same AS.
The correct protocol in that case would be iBGP (internal BGP) if BGP were to be used within the
➡
AS.
Therefore, the correct answer is: D. eBGP
Reference:
Nokia IP Routing Fundamentals – BGP vs IGP
Nokia SRA Guide – AS Concepts and Protocol Suitability
RFC 4271 – BGP Specification
Question 11
Which of the following statements about the OSPF routing protocol is FALSE?
- A. It is a link state protocol.
- B. It supports hierarchy using multiple areas.
- C. It uses a mechanism for routers to exchange topology information.
- D. It uses hop-count for route selection.
Answer:
D
Explanation:
OSPF (Open Shortest Path First) is a Link-State protocol that uses:
Cost (based on bandwidth) as its metric.
Dijkstra’s algorithm to compute shortest path trees.
Supports hierarchical routing with areas (e.g., Area 0 as backbone).
Routers exchange LSAs, not full routing tables.
Option D is FALSE – OSPF does not use hop-count. That’s a RIP (Distance Vector) feature.
Reference:
Nokia IP Routing Guide – Section: “OSPF Operation and Area Design”
RFC 2328 – OSPFv2 Protocol Specification
Question 12
Which of the following is a characteristic of Link State protocols?
- A. Routers send a copy of their entire routing table to their neighbors.
- B. Routers send periodic routing table updates to the entire network.
- C. Routers know the entire network topology.
- D. Routers use hop-count to calculate their routing tables.
Answer:
C
Explanation:
Link-State routing protocols (e.g., OSPF, IS-IS) operate by:
Each router flooding link-state advertisements (LSAs) throughout the network.
Every router constructs a complete map of the network topology.
Then each router runs the SPF algorithm to compute optimal paths.
Option C is correct – routers know the entire network topology.
Option A is Distance Vector behavior (e.g., RIP).
Option B is not efficient or accurate for Link-State.
Option D – hop-count is used in Distance Vector (e.g., RIP).
Reference:
Nokia SRA Study Guide – Chapter: “OSPF and IS-IS Concepts”
RFC 2328 – OSPF Link-State Overview
Question 13
Which of the following types of information is used to calculate the Shortest Path Tree (SPT)?
- A. Copies of the neighbors' routing tables
- B. Hop count to each potential destination
- C. Network topology
- D. IP reachability
Answer:
C
Explanation:
The Shortest Path Tree (SPT) is calculated by Link-State routing protocols like OSPF and IS-IS using:
A complete map of the network topology.
Each router uses algorithms like Dijkstra’s to compute the shortest paths to all destinations.
Option C is correct – full network topology is used.
Option A refers to Distance Vector methods.
Option B and D are results of topology analysis but not the input used.
Reference:
Nokia Routing Protocols Guide – Section: “SPT and Link-State Behavior”
RFC 2328 – OSPF Specification
Question 14
Which of the following is a characteristic of a static route?
- A. Exchanges routes with neighboring routers periodically.
- B. Can only be used for routing within an autonomous system.
- C. Uses a hop-count metric to determine the best route to a network.
- D. Explicitly defines the next-hop based on operator input.
Answer:
D
Explanation:
A static route is a manually configured route added by a network administrator. It does not rely on
dynamic routing protocols or metrics.
It does not exchange routes with other routers (A – false).
It can be used both within or across ASes (B – false).
It does not use metrics like hop count (C – false).
Option D is correct – the operator explicitly defines the next-hop IP or egress interface manually.
Static routes are often used for:
Default routing
Backup routing
Simple or small networks
Reference:
Nokia IP Fundamentals – Chapter: “Static vs Dynamic Routing”
Question 15
What is the sequence of messages that must be exchanged between a DHCP client and a server for
the client to receive an IP address?
- A. Discover, Offer, Request, Acknowledgement
- B. Request, Offer, Discover, Acknowledgement
- C. Discover, Acknowledgement, Request, Offer
- D. Request, Acknowledgement, Discover, Offer
Answer:
A
Explanation:
The DHCP client/server exchange follows a specific four-step sequence known as DORA:
Discover – Client broadcasts to find available DHCP servers.
Offer – DHCP server responds with an IP address offer.
Request – Client requests the offered IP.
Acknowledgement – Server confirms the lease.
This ensures dynamic IP configuration and is used in enterprise and home networks.
Reference:
Nokia IP Fundamentals Guide – DHCP Protocol Operation
RFC 2131 – Dynamic Host Configuration Protocol