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Nokia VPLS practice questions

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Question 1VPLS fundamentals and architecture

In a VPLS, which mechanism makes a customer Ethernet frame with an unknown destination MAC address reach every other PE in the same VPLS instance?

  1. Flooding over the established pseudowire mesh Correct answer.
  2. Anycast ARP proxying at the CE edge
  3. Static MAC pinning on each PE
  4. STP root election across the provider core

Explanation

A VPLS emulates a LAN segment, so unknown unicast, broadcast and multicast frames must be flooded to all other PEs participating in that VPLS instance. This flooding is sent over the full mesh of pseudowires that connects the PE routers. Learned MAC addresses are later used to forward unicast frames over a single pseudowire.

Question 2VPLS fundamentals and architecture

What does a pseudowire provide in a VPLS deployment?

  1. A routing adjacency between PE loopback addresses
  2. A Layer 3 VPN instance bound to a VRF
  3. A point-to-point emulated Ethernet service between two PEs Correct answer.
  4. A label-switched path used only for IPv4 traffic

Explanation

A pseudowire is a point-to-point emulated wire that carries customer Ethernet frames between two provider edge devices over the packet-switched network. In VPLS, many such pseudowires are combined into a full mesh to emulate a single bridged LAN. The pseudowire itself is not a routing adjacency or a Layer 3 VPN construct.

Question 3VPLS fundamentals and architecture

Which forwarding decision does a PE make for a known unicast frame received from a local attachment circuit in a VPLS?

  1. Flood the frame to all pseudowires in the instance
  2. Send the frame to the VPLS route reflector for resolution
  3. Look up the destination IP prefix in the global routing table
  4. Look up the destination MAC in the VPLS MAC table and send it on the mapped pseudowire Correct answer.

Explanation

VPLS forwards on Layer 2 information, so the PE learns source MAC addresses per attachment circuit and per pseudowire and builds a MAC forwarding table for each VPLS instance. A known unicast destination is mapped to the pseudowire or local port associated with that MAC. Unknown destinations are flooded instead, and IP lookups are not involved.

Question 4VPLS fundamentals and architecture

What is the role of a VPLS instance identifier, such as a service ID, on a Nokia PE?

  1. It determines the spanning tree priority of the PE
  2. It identifies the physical SAP port on the access node
  3. It uniquely identifies the emulated LAN and scopes MAC learning to that instance Correct answer.
  4. It sets the pseudowire label value used on the core

Explanation

Each VPLS service is a separate emulated LAN, so its identifier scopes MAC learning, flooding and pseudowire membership to that instance. Frames belonging to different service IDs are never bridged together even if they arrive on the same physical port. The identifier is a local service construct rather than a label or port number.

Question 5VPLS fundamentals and architecture

Which statement describes the control-plane difference between VPLS and a Layer 3 VPN?

  1. VPLS distributes MAC addresses with BGP while an L3 VPN learns IP prefixes in the data plane
  2. VPLS requires a route reflector to learn customer IP prefixes
  3. VPLS distributes MAC reachability through data-plane learning, while an L3 VPN distributes IP prefixes by routing protocols Correct answer.
  4. Both rely on IS-IS to distribute customer MAC addresses

Explanation

Traditional VPLS does not run a routing protocol for customer addresses; each PE learns customer MAC addresses by inspecting frames in the data plane. A Layer 3 VPN instead distributes customer IP prefixes through routing protocols over the provider core. This difference is why MAC scaling and unknown unicast flooding are VPLS-specific concerns.

Question 6VPLS fundamentals and architecture

What does the attachment circuit, often configured as a SAP, represent in a VPLS service?

  1. The customer-facing interface where customer frames enter and leave the VPLS Correct answer.
  2. The BGP session toward the route reflector
  3. The loopback address used for pseudowire signaling
  4. The tunnel label path across the provider backbone

Explanation

The attachment circuit is the customer-facing edge of the service, and on Nokia equipment it is typically configured as a service access point on a port with an encapsulation value. It is where customer Ethernet frames are mapped into the VPLS instance. Core transport and signaling constructs are separate from this access point.

Question 7VPLS fundamentals and architecture

Which encapsulation commonly carries a pseudowire across an MPLS-enabled provider core in a VPLS?

  1. A plain Ethernet frame with no provider header
  2. A GRE tunnel with no service demultiplexing field
  3. An MPLS label stack with a service label over a tunnel label Correct answer.
  4. An IP-in-IP tunnel keyed by the customer VLAN

Explanation

VPLS pseudowires are typically carried in MPLS, using an inner service label to identify the pseudowire or VPLS instance and an outer tunnel label to reach the remote PE. The label stack lets the remote PE demultiplex the frame into the correct service. Encapsulations without a service demultiplexing field cannot distinguish VPLS instances on the same tunnel.

Question 8VPLS fundamentals and architecture

Why does a basic VPLS design require a full mesh of pseudowires between the participating PEs?

  1. To allow each PE to run a separate routing protocol instance
  2. To reduce the number of labels required per service
  3. To avoid forwarding loops while still delivering flooded frames to every PE Correct answer.
  4. To ensure all customer VLANs are terminated at a single PE

Explanation

A full mesh gives every PE a direct pseudowire to every other PE, so flooded frames reach all members without relaying through intermediate PEs. If flooding were relayed through other PEs, loops and duplicate delivery could occur. The mesh therefore replaces the need for a loop-breaking protocol in the provider core for basic VPLS.

Question 9VPLS fundamentals and architecture

A PE receives a frame whose destination MAC address is present in its VPLS MAC table but associated with a remote pseudowire. What does the PE do?

  1. It forwards the frame over that pseudowire without flooding to other PEs Correct answer.
  2. It drops the frame because remote MAC entries are not usable
  3. It floods the frame to all pseudowires and waits for a reply
  4. It sends the frame to the route reflector for resolution

Explanation

Once a MAC address is learned from a pseudowire, the PE treats it as reachable over that pseudowire and forwards known unicast traffic directly. Flooding is reserved for unknown, broadcast and multicast destinations. Dropping or control-plane resolution would defeat the purpose of data-plane MAC learning.

Question 10VPLS fundamentals and architecture

A customer sends a broadcast frame into a VPLS with four participating PEs. How is the frame handled?

  1. It is converted to unicast toward the nearest PE
  2. It is discarded because broadcast is not supported in VPLS
  3. It is sent only to the PE holding the spanning tree root
  4. It is replicated to every other PE in the same VPLS instance Correct answer.

Explanation

Broadcast frames must reach every member of the emulated LAN, so the ingress PE replicates the frame onto each pseudowire in the instance except the one it arrived on. This preserves LAN semantics for protocols such as ARP. VPLS does not filter broadcast or convert it to unicast.

Question 11VPLS fundamentals and architecture

Why is MAC address learning disabled or restricted on pseudowire ports toward the provider core in some VPLS designs?

  1. To force all traffic to use the management VRF
  2. To allow the core to run transparent bridging
  3. To prevent core-facing MAC addresses from being learned into the customer forwarding table Correct answer.
  4. To reduce the pseudowire label space on the PE

Explanation

Provider core addresses are not customer stations, so learning them into the VPLS MAC table would waste table space and could cause misforwarding. Restricting learning on network-facing ports keeps the table populated only with customer MAC addresses. This practice does not affect label allocation or core bridging.

Question 12VPLS fundamentals and architecture

A VPLS service must connect customer sites that use the same VLAN ID on their attachment circuits. What must the provider do at the SAP?

  1. Rewrite all customer VLANs to VLAN 1
  2. Enable IP routing between the sites
  3. Map the customer VLAN to a service-specific encapsulation so instances remain distinct Correct answer.
  4. Disable MAC learning on the SAP

Explanation

When multiple customers or instances reuse the same VLAN ID, the provider must map each customer VLAN to a distinct service encapsulation so frames are not merged. This preserves separation between VPLS instances. Rewriting to a common VLAN or disabling learning would break that separation.

Question 13VPLS fundamentals and architecture

What happens when a PE's VPLS MAC table reaches its configured limit for a service?

  1. The PE floods all frames regardless of destination
  2. The service is shut down and all pseudowires are torn down
  3. New source MAC addresses are not learned until entries age out or are cleared Correct answer.
  4. The PE automatically expands the table and continues learning

Explanation

A MAC limit bounds the table size to protect PE memory and stability. When the limit is reached, additional source addresses are not learned, so traffic to them is flooded until space becomes available. The PE does not automatically resize the table or tear down the service.

Question 14VPLS fundamentals and architecture

Which problem can occur if a VPLS full mesh is replaced by a hub-and-spoke pseudowire topology without additional loop prevention?

  1. BGP will withdraw the VPLS route targets
  2. MAC addresses can no longer be learned on any PE
  3. Flooded frames relayed through the hub can be duplicated or looped back to the origin Correct answer.
  4. The service label stack becomes invalid on the hub

Explanation

In a partial mesh, flooded frames must be relayed by intermediate PEs, and without split-horizon or similar loop prevention the hub can send a frame back toward the PE it came from. That causes duplication or looping. MAC learning and label validity are not inherently broken by the topology change.

Question 15VPLS fundamentals and architecture

How does a PE know which remote PEs belong to the same VPLS instance?

  1. Through ARP requests sent to the provider core
  2. Through BGP auto-discovery using route targets and a service identifier Correct answer.
  3. Through the spanning tree topology learned from customer bridges
  4. Through static host routes installed by the CE

Explanation

VPLS auto-discovery uses BGP to advertise membership, with route targets controlling import and export and a service identifier distinguishing instances. Each PE then knows which remote PEs are members and can set up pseudowires to them. ARP, spanning tree and CE host routes do not provide provider-side membership discovery.

Question 16VPLS fundamentals and architecture

A PE learns the same MAC address from two different pseudowires in the same VPLS instance. What is the typical immediate result?

  1. The PE load-balances traffic across both pseudowires
  2. The PE updates the entry to the most recently learned pseudowire Correct answer.
  3. The PE raises an alarm and discards both entries
  4. The PE permanently blocks one pseudowire

Explanation

MAC learning follows the most recent observation, so a duplicate address causes the entry to move to the newly learned pseudowire. This can produce intermittent forwarding if the duplication is caused by a loop or misconfiguration. The PE does not normally block a pseudowire or load-balance on a duplicate MAC.

Question 17VPLS fundamentals and architecture

What is the purpose of a split-horizon rule in VPLS forwarding?

  1. To prevent a flooded frame from being sent back out the pseudowire it arrived on Correct answer.
  2. To divide the MAC table between access and core ports
  3. To split the service label range between PEs
  4. To separate customer VLANs into different VRFs

Explanation

Split horizon ensures that a flooded frame received on one pseudowire is not forwarded back out that same pseudowire. This is essential in partial-mesh or hierarchical designs where PEs relay flooded traffic. It does not partition MAC tables, label ranges or VRFs.

Question 18VPLS fundamentals and architecture

Which statement best explains why VPLS is described as a Layer 2 multipoint service rather than a collection of point-to-point circuits?

  1. Each site must be manually paired with one remote site
  2. The service requires a separate instance per direction of traffic
  3. A single instance provides any-to-any connectivity among all attached sites Correct answer.
  4. The service forwards only IP packets between sites

Explanation

VPLS presents one emulated LAN to all attached sites, so any site can reach any other within the same instance without per-pair circuit provisioning. This any-to-any property distinguishes it from a set of point-to-point pseudowires. It is independent of the payload protocol and does not require per-direction instances.

Question 19VPLS fundamentals and architecture

A customer bridge connected to a VPLS runs spanning tree. What is the provider's typical concern regarding that customer BPDUs?

  1. BPDUs are converted into MPLS OAM messages
  2. BPDUs are used by the provider to elect the pseudowire mesh root
  3. BPDUs are carried transparently across the VPLS and can influence the customer topology Correct answer.
  4. BPDUs are terminated at the ingress PE and never forwarded

Explanation

VPLS is transparent to Layer 2 control frames, so customer BPDUs are flooded across the emulated LAN and can affect the customer spanning tree topology. The provider must therefore consider whether customer BPDUs should be tunneled or filtered at the edge. They are not terminated, converted to OAM, or used for provider mesh election.

Question 20VPLS fundamentals and architecture

Which scalability concern is specific to VPLS compared with a Layer 3 VPN?

  1. The provider must distribute customer IP prefixes with BGP
  2. The provider must run a routing protocol on each SAP
  3. The provider must allocate a unique AS number per customer
  4. The provider must learn and maintain customer MAC addresses per instance Correct answer.

Explanation

Because VPLS forwards on Layer 2, each PE must learn customer MAC addresses for every instance it serves, which drives table size and aging behavior. Layer 3 VPNs instead distribute IP prefixes through routing protocols. SAP routing and per-customer AS numbers are not VPLS requirements.

Question 21VPLS fundamentals and architecture

In a hierarchical VPLS design, what function does a spoke PE perform for flooded traffic received from its access side?

  1. It forwards the flooded frame to the hub PE, which replicates it to other spokes Correct answer.
  2. It converts the frame into a multicast IP packet
  3. It reflects the frame back to its own access ports only
  4. It drops the frame to avoid core flooding

Explanation

In hierarchical VPLS, spoke PEs send flooded traffic to the hub, and the hub replicates it toward the other spokes, reducing the number of pseudowires each spoke must maintain. Split-horizon rules at the hub prevent the frame from being sent back to the originating spoke. Spokes do not drop flooded traffic or convert it to IP multicast.

Question 22VPLS fundamentals and architecture

A PE receives a frame on an attachment circuit and the destination MAC is unknown, but the PE has a MAC limit configured and the table is full. What is the forwarding result?

  1. The frame is flooded to the other pseudowires in the instance and the new source is not learned Correct answer.
  2. The frame is returned to the originating attachment circuit
  3. The frame is unicast to the hub PE only
  4. The frame is dropped because the table is full

Explanation

Reaching the MAC limit stops new learning but does not stop forwarding, so an unknown destination is still flooded to the other members of the instance. The source address simply is not added to the table. Dropping the frame, unicasting to a hub, or returning it to the sender are not the defined behaviors.

Question 23VPLS fundamentals and architecture

Why can a VPLS instance deliver frames between two sites even when the customer uses non-IP protocols such as LLDP or proprietary Layer 2 frames?

  1. The service forwards on MAC addresses and is transparent to the Layer 3 payload Correct answer.
  2. The service converts non-IP frames into MPLS OAM packets
  3. The service requires all payloads to be encapsulated in IPv4
  4. The service inspects and rewrites the EtherType field at each PE

Explanation

VPLS forwards based on Ethernet MAC addresses, so it does not need to interpret the Layer 3 payload. This transparency lets non-IP and proprietary Layer 2 frames traverse the emulated LAN. The provider does not rewrite EtherTypes, require IPv4 encapsulation, or convert frames into OAM.

Question 24VPLS fundamentals and architecture

Which combination correctly orders the labels a remote PE typically sees on a VPLS frame arriving over an MPLS core?

  1. A GRE header followed by a VLAN tag
  2. Inner service label first, then outer tunnel label
  3. Outer tunnel label first, then inner service label identifying the pseudowire Correct answer.
  4. Only a single label that identifies both tunnel and service

Explanation

The label stack places the tunnel label outermost so core routers can forward the packet toward the remote PE, with the service label beneath it to identify the pseudowire or instance. The remote PE pops the tunnel label and uses the service label for demultiplexing. A single label or a GRE header would not provide both functions.

Question 25VPLS fundamentals and architecture

An operator wants to reduce unknown unicast flooding in a VPLS without changing the Layer 2 service model. Which approach is consistent with VPLS architecture?

  1. Enable MAC address aging tuning and MAC flush on topology changes so tables stay accurate Correct answer.
  2. Convert the VPLS into a Layer 3 VPN
  3. Replace all pseudowires with static IP routes
  4. Disable MAC learning entirely on all PEs

Explanation

Unknown unicast flooding is reduced when MAC tables accurately reflect current locations, so aging parameters and MAC flush on failures help keep entries correct. Disabling learning would increase flooding rather than reduce it. Static IP routes or converting to a Layer 3 VPN change the service model entirely.

Question 26VPLS fundamentals and architecture

In a VPLS, which functional element is the provider edge device that maintains the per-service MAC forwarding table and the set of pseudowires belonging to that service?

  1. The CE, which performs label imposition toward the core
  2. The route reflector, which distributes MAC reachability to the PEs
  3. The P router, which stores customer MAC addresses per VPLS
  4. The PE, which acts as a virtual bridge instance for each VPLS Correct answer.

Explanation

In VPLS the provider edge holds a virtual bridge instance per service; that instance owns the MAC table and the mesh of pseudowires toward the other participating PEs. Core P routers only switch labeled traffic and have no knowledge of customer MAC addresses or VPLS membership. The CE is the customer device and never performs provider label operations.

Question 27VPLS fundamentals and architecture

Which statement describes the forwarding behavior of a VPLS instance when it receives a frame whose destination MAC address has been learned on a remote pseudowire?

  1. The frame is sent only on the pseudowire associated with that MAC address Correct answer.
  2. The frame is dropped because VPLS never forwards known unicast
  3. The frame is forwarded to the core P routers, which look up the customer MAC
  4. The frame is flooded to every pseudowire and attachment circuit in the instance

Explanation

Once a destination MAC is present in the VPLS MAC table and mapped to a particular pseudowire, the PE performs a targeted forwarding decision and sends the frame only over that pseudowire. Flooding is reserved for broadcast, multicast, and unknown unicast traffic. This selective forwarding is what distinguishes VPLS from simple Layer 2 flooding domains.

Question 28VPLS fundamentals and architecture

What is the essential role of the VPLS instance identifier (such as a VPLS ID or service ID) exchanged between PEs?

  1. It defines the spanning tree priority used by the provider core
  2. It determines the MPLS label value assigned to the transport tunnel
  3. It sets the VLAN tag value used on the attachment circuits
  4. It allows each PE to decide which remote PEs and pseudowires belong to the same Layer 2 service Correct answer.

Explanation

PEs must agree on which pseudowires belong to which customer service, and a service identifier carried in the signaling (for example in BGP or LDP-based autodiscovery) provides that binding. Without a common identifier, a PE could not tell whether a given remote pseudowire should be attached to a particular virtual bridge instance. The identifier is a membership key, not a tag value or label value.

Question 29VPLS fundamentals and architecture

Why does a VPLS need a loop-prevention mechanism such as split horizon when a PE has more than one pseudowire in the same service?

  1. Because MAC learning is disabled on all attachment circuits in a VPLS
  2. Because a frame flooded into the mesh could otherwise be relayed from one pseudowire back out to another and circulate indefinitely Correct answer.
  3. Because attachment circuits always carry the same VLAN ID at every site
  4. Because MPLS labels can be reused by different PEs in the same service

Explanation

In a full mesh of pseudowires, a broadcast or unknown unicast frame arriving from one pseudowire must not be forwarded out to the other pseudowires of the same instance, or it would loop between PEs. Split horizon enforces this rule by treating the pseudowire mesh as a set of spokes from the PE's perspective. The mechanism is about forwarding topology, not about label reuse or VLAN values.

Question 30VPLS fundamentals and architecture

An operator deploys a VPLS with four PEs in a full mesh. A new site must be added, bringing the mesh to five PEs. How does the number of pseudowires in the full mesh change?

  1. It stays at 6 because the new PE only connects to one existing PE
  2. It grows from 4 to 5 pseudowires
  3. It grows from 12 to 20 pseudowires
  4. It grows from 6 to 10 pseudowires Correct answer.

Explanation

A full mesh among n PEs requires n(n-1)/2 pseudowires, so four PEs need 6 and five PEs need 10. Each added PE must establish a pseudowire to every existing PE, which is why full-mesh VPLS scales quadratically with the number of sites. Hierarchical VPLS designs exist to contain this growth.

Question 31VPLS fundamentals and architecture

A service provider wants to offer a VPLS where customer sites in different metropolitan regions attach to regional PEs, and those regional PEs connect through a small number of core PEs. Which design addresses the pseudowire scaling problem while preserving multipoint service?

  1. Removing all pseudowires and relying on the attachment circuits to bridge between regions
  2. Configuring the regional PEs as pure P routers that forward only labeled traffic
  3. Replacing the VPLS with a set of point-to-point pseudowires between every pair of regional PEs
  4. Hierarchical VPLS, with spoke PEs homing to hub or core PEs that relay traffic between regions Correct answer.

Explanation

Hierarchical VPLS introduces hub PEs that aggregate spoke PEs; spokes establish pseudowires to their hub rather than to every other spoke, which reduces the pseudowire count while keeping multipoint connectivity. The hub relays flooded traffic between spokes under split-horizon rules. Point-to-point pseudowire meshes and pure P-router roles do not deliver this scaling benefit.

Question 32VPLS fundamentals and architecture

Two customer sites connected to the same VPLS use untagged Ethernet frames on their attachment circuits, while the provider core carries the service with MPLS encapsulation. What must the PE do to the customer frame before sending it over a pseudowire?

  1. Push the service and transport labels and forward the frame over the pseudowire Correct answer.
  2. Leave the frame unchanged and rely on the core to add labels at each hop
  3. Convert the Ethernet frame into an IP packet and route it across the core
  4. Rewrite the customer destination MAC address to the remote PE's address

Explanation

The ingress PE encapsulates the customer Ethernet frame with the label stack needed for the pseudowire and the transport tunnel, then forwards it as an MPLS packet. The customer frame itself, including its MAC header, is preserved inside the encapsulation. The remote PE removes the labels and delivers the original frame on the correct attachment circuit.

Question 33VPLS fundamentals and architecture

A PE in a VPLS receives a frame from an attachment circuit whose destination MAC address is a multicast address used by the customer's routing protocol. How should the PE treat this frame?

  1. Send it to the core P routers for replication to the other PEs
  2. Forward it only toward the pseudowire that previously carried traffic from that MAC address
  3. Discard it because multicast addresses are not permitted in a VPLS
  4. Flood it to all other attachment circuits and pseudowires in the instance, subject to split horizon Correct answer.

Explanation

Multicast destination addresses are never learned as source addresses, so the PE cannot have a unicast entry for them. The frame is treated as flooded traffic and replicated to every other member of the instance, with split horizon preventing it from being sent back out the pseudowire it arrived on. Replication is performed by the PEs, not by core P routers.

Question 34VPLS fundamentals and architecture

An operator is concerned about the amount of unknown unicast flooding in a large VPLS. Which approach reduces flooding while keeping the same Layer 2 multipoint service model?

  1. Disabling MAC learning on all attachment circuits
  2. Enabling a mechanism that pre-populates or synchronizes MAC reachability so more destinations are known before traffic arrives Correct answer.
  3. Replacing the VPLS with a Layer 3 VPN so that no flooding occurs
  4. Removing the full mesh and connecting every PE in a ring

Explanation

Flooding occurs only for destinations that are not yet in the MAC table, so techniques that populate or distribute MAC reachability in advance reduce unknown unicast. Examples include control-plane MAC advertisement or tighter aging and learning tuning that keeps entries fresh. Changing the service to Layer 3 or disrupting the topology changes the service model rather than optimizing flooding within VPLS.

Question 35VPLS fundamentals and architecture

A customer connects a site to a VPLS through an attachment circuit that carries several VLANs, and the provider maps each VLAN to a distinct VPLS instance. What is this deployment commonly called?

  1. A hierarchical VPLS with a spoke PE per VLAN
  2. A point-to-point pseudowire with no service multiplexing
  3. VLAN-based service multiplexing, where each VLAN selects a different VPLS Correct answer.
  4. A single flat VPLS with one shared MAC table for all VLANs

Explanation

When a single attachment circuit carries multiple VLANs and each VLAN is mapped to a separate VPLS instance, the provider is multiplexing services on that port. Each instance keeps its own MAC table and pseudowire set, preserving customer separation. This differs from a flat VPLS, where all traffic shares one bridge instance.

Question 36VPLS fundamentals and architecture

Why can a VPLS forward customer frames carrying non-IP protocols, such as LLDP or proprietary Layer 2 frames, between sites without additional provider configuration?

  1. Because the service forwards Ethernet frames based on MAC addresses and does not require the payload to be IP Correct answer.
  2. Because LLDP frames are always intercepted by the provider edge and regenerated at the remote site
  3. Because non-IP frames are flooded only to attachment circuits and never to pseudowires
  4. Because the PE inspects the EtherType and converts unknown protocols to IP

Explanation

VPLS is a Layer 2 service: forwarding decisions are made on Ethernet MAC addresses, so the EtherType and upper-layer protocol are irrelevant to delivery. Any frame the customer sends, IP or not, is carried across the pseudowire mesh as long as the MAC forwarding state permits it. This protocol transparency is a defining property of the service.

Question 37VPLS fundamentals and architecture

In a VPLS, a PE learns a customer MAC address from a pseudowire and later learns the same MAC address from a local attachment circuit. What is the standard immediate result for that MAC entry?

  1. The entry is updated to point to the attachment circuit, and traffic for that MAC is sent locally Correct answer.
  2. The PE raises an alarm and drops all traffic for that MAC address
  3. The entry is duplicated so that traffic is load-shared between the two paths
  4. The entry is deleted and the MAC is blocked until an administrator clears it

Explanation

MAC learning follows the most recent observation: when the same address appears on a different port, the PE moves the entry to the new port. In this case the address has moved to the local access side, so subsequent traffic is delivered locally rather than over the pseudowire. This behavior supports site moves and redundancy without manual intervention.

Question 38VPLS fundamentals and architecture

A provider is comparing VPLS with a Layer 3 VPN for a customer that needs to run its own routing protocol between sites and keep the provider unaware of customer IP addressing. Which characteristic of VPLS supports this requirement?

  1. The service requires the customer to use provider-assigned IP addresses at every site
  2. The provider core must run the customer's routing protocol to forward frames
  3. The provider edge forwards on customer MAC addresses, so customer IP addressing stays invisible to the provider Correct answer.
  4. The provider edge maintains a per-service IP routing table for each customer

Explanation

Because VPLS forwards Ethernet frames based on MAC addresses, the provider does not need to know or carry customer IP routes. The customer's routing protocol runs between customer devices as if they shared a LAN, and the provider remains a Layer 2 transport. A Layer 3 VPN, by contrast, requires the provider to participate in customer routing.

Question 39VPLS fundamentals and architecture

A PE in a VPLS has a MAC limit configured for the service, and the table is full. A new frame arrives with a source MAC address not currently in the table. What is the typical immediate behavior?

  1. The new source is not learned, and frames from it may be flooded or dropped depending on the implementation Correct answer.
  2. The new source is learned and the oldest entry is evicted to make room
  3. The entire MAC table is flushed and relearning starts from scratch
  4. The service is shut down until the table falls below the limit

Explanation

When the configured MAC limit is reached, the PE stops adding new entries, so the new source address is not learned. Its traffic is then handled as unknown, typically flooded within the instance or dropped if the platform enforces a stricter policy. Existing entries are retained so that established flows keep working.

Question 40VPLS fundamentals and architecture

An operator runs a VPLS across an MPLS core and wants to verify how a customer frame is carried end to end. Which description correctly reflects the encapsulation a PE applies on the ingress side?

  1. A VLAN tag stack that the core P routers use to identify the VPLS instance
  2. A single label that identifies both the transport tunnel and the customer VPLS instance
  3. An IP header with a GRE tunnel carrying the customer Ethernet frame and no MPLS labels
  4. An outer transport label, an inner service or pseudowire label, and the customer Ethernet frame Correct answer.

Explanation

The ingress PE pushes a label stack consisting of an outer transport label used to reach the egress PE and an inner service label that identifies the pseudowire or VPLS instance. The customer Ethernet frame is carried inside this encapsulation. The egress PE pops the labels and forwards the original frame to the attachment circuit.

Question 41VPLS service configuration and provisioning

In a Nokia VPLS service, which identifier uniquely names the VPLS instance within the service delivery model and is used to bind SAPs and SDPs together?

  1. SDP far-end address
  2. Service ID (service-id) Correct answer.
  3. VPLS site name
  4. SAP port ID

Explanation

The service-id is the numeric identifier that defines the VPLS instance in the service model; SAPs and mesh or spoke SDPs are bound to that service-id. Port IDs and far-end addresses identify endpoints but do not name the VPLS instance itself.

Question 42VPLS service configuration and provisioning

Which Nokia service type must be selected when provisioning a VPLS so that MAC learning and flooding behave as a multipoint bridged service?

  1. Vprn
  2. Ies
  3. Epipe
  4. VPLS Correct answer.

Explanation

A VPLS service type provides multipoint Ethernet bridging with MAC learning and flooding across SAPs and SDPs. Epipe is point-to-point, Vprn is IP/MPLS routing, and Ies is internet-enhanced service, none of which provide the VPLS bridging behavior.

Question 43VPLS service configuration and provisioning

When configuring a mesh SDP for a VPLS, which parameter must match on both PE routers for the pseudowire to establish?

  1. The SAP encapsulation type
  2. The ingress QoS policy name
  3. The customer VLAN tag
  4. The VC ID (virtual circuit identifier) Correct answer.

Explanation

The VC ID must match on both ends of an SDP binding so the pseudowire endpoints are paired correctly. SAP encapsulation, QoS policy names, and VLAN tags are locally significant and do not need to match across the tunnel.

Question 44VPLS service configuration and provisioning

A VPLS uses a full mesh of SDPs between three PEs. What is the primary purpose of the mesh SDP bindings in this design?

  1. To carry management traffic between PEs
  2. To provide a point-to-point backup path per SAP
  3. To synchronize routing tables between PEs
  4. To enable multipoint forwarding between all PE sites Correct answer.

Explanation

Mesh SDPs create a full-mesh of pseudowires so that every PE can forward bridged traffic directly to every other PE, giving multipoint connectivity. They do not carry management traffic, act as per-SAP backups, or synchronize routing tables.

Question 45VPLS service configuration and provisioning

Which statement describes the role of a spoke SDP in a hierarchical VPLS design?

  1. It carries only multicast traffic between PEs
  2. It connects a PE to a single remote PE, typically toward a hub Correct answer.
  3. It is used exclusively for management access
  4. It provides local SAP-to-SAP switching only

Explanation

A spoke SDP is a single pseudowire binding toward one remote PE, commonly used in hub-and-spoke or hierarchical VPLS to concentrate traffic at a hub. It does not provide local-only switching, multicast-only transport, or management-only access.

Question 46VPLS service configuration and provisioning

When a SAP is created on a port for a VPLS, which encapsulation value is typically used for a customer-tagged Ethernet access?

  1. null
  2. frame-relay
  3. qinq
  4. dot1q Correct answer.

Explanation

Dot1q encapsulation is used when a single customer VLAN tag identifies the SAP on the access port. Null is for untagged traffic, qinq is for stacked tags, and frame-relay is not an Ethernet encapsulation.

Question 47VPLS service configuration and provisioning

What does a null-encapsulated SAP on a VPLS access port expect to receive?

  1. Untagged traffic Correct answer.
  2. Traffic with two stacked VLAN tags
  3. Traffic with a single VLAN tag
  4. MPLS-labeled traffic

Explanation

Null encapsulation means the SAP accepts untagged frames on the access port. Single-tag traffic uses dot1q, stacked tags use qinq, and MPLS labels belong to the transport, not the access SAP.

Question 48VPLS service configuration and provisioning

Which MAC learning behavior is enabled by default on a VPLS service in Nokia SR OS?

  1. MAC learning occurs only on spoke SDPs
  2. MAC learning is disabled until manually enabled
  3. MAC learning occurs only on null SAPs
  4. MAC learning is enabled on SAPs and SDPs Correct answer.

Explanation

By default a VPLS learns source MAC addresses on its SAPs and SDP bindings to build the forwarding database. It is not disabled by default, nor restricted to spoke SDPs or null SAPs.

Question 49VPLS service configuration and provisioning

A VPLS must not flood unknown unicast frames to a particular SAP used for a single server. Which feature should be configured on that SAP?

  1. Split horizon
  2. MAC pinning
  3. Ingress filtering
  4. Restricted (no unknown flooding) Correct answer.

Explanation

Marking a SAP as restricted prevents unknown unicast, broadcast, and multicast flooding to it, which suits a single-server attachment. MAC pinning fixes a MAC to a SAP, split horizon prevents loops, and ingress filtering drops frames from unknown sources.

Question 50VPLS service configuration and provisioning

Which mechanism prevents a frame received on a SAP from being forwarded back out the same SAP in a VPLS?

  1. MAC aging
  2. Split horizon Correct answer.
  3. QoS marking
  4. IGMP snooping

Explanation

Split horizon prevents a frame from being reflected back out the binding on which it arrived, avoiding loops and duplicate delivery. MAC aging manages the forwarding table, IGMP snooping controls multicast, and QoS marking handles prioritization.