Question 1

Click on the exhibit below. https://kxbjsyuhceggsyvxdkof.supabase.co/storage/v1/object/public/file-images/NOKIA_4A0-105/page_14_img_1.jpg The MDU attached to this PE has been configured with active/standby SDP's configuration option has been configured for the PE to recognize that this SDP is in standby mode?

Accepted Answer

D

Explanation: For a PE router to recognize that a remote SDP is in standby mode, the remote router (the MDU) must advertise this status. The no suppress-standby-signaling command, which is the default configuration, enables this signaling. When configured on the MDU's VPLS service endpoint, it instructs the MDU to send a Targeted LDP (T-LDP) label withdrawal message containing a "standby" status code to the local PE. This signal allows the local PE to correctly identify the SDP's operational state as standby, ensuring it is not used for forwarding traffic until the active path fails.

Question 2

Click on the exhibit below. https://kxbjsyuhceggsyvxdkof.supabase.co/storage/v1/object/public/file-images/NOKIA_4A0-105/page_57_img_2.jpg CE-A sends frames with 2 tags. If the SAP on PE-A is "sap 1/1/1:1 .*" and the SAP on PE-B is "sap 1/1/1:100.200" how many tags will there be on the frame when it egresses from the SAP on PE-B?

Accepted Answer

C

Explanation: The frame processing follows these steps: 1. Ingress (PE-A): CE-A sends a frame with two VLAN tags. The ingress SAP is sap 1/1/1:1.. This is a QinQ SAP that matches an outer tag of 1 and any inner tag. The outer tag (S-tag) is the service delimiter and is stripped. The inner tag (C-tag) is preserved and forwarded into the VPLS instance. The frame now has one tag inside the service. 2. Egress (PE-B): The frame, with its single C-tag, arrives at PE-B. It is destined for the egress SAP 1/1/1:100.200. This SAP definition dictates the exact encapsulation for frames leaving the port. The router strips the C-tag that was carried across the service and pushes two new tags: an outer tag of 100 and an inner tag of 200. The resulting frame has two tags.

Question 3

Click on the exhibit below. https://kxbjsyuhceggsyvxdkof.supabase.co/storage/v1/object/public/file-images/NOKIA_4A0-105/page_11_img_1.jpg Based on the output below which of the following statements is true?

Accepted Answer

D

Explanation: The output shows that the Designated Bridge ID (32768.00:19:db:00:00:02) on the Root Port (sap-1/1/1:100) is identical to the overall Root Bridge Id. This signifies that the local bridge is receiving its best Bridge Protocol Data Units (BPDUs) directly from the Root Bridge itself. A non-root bridge that is directly connected to the Root Bridge has the shortest possible path, making it the closest bridge to the root in the Spanning Tree topology.

Question 4

Click on the exhibit below. https://kxbjsyuhceggsyvxdkof.supabase.co/storage/v1/object/public/file-images/NOKIA_4A0-105/page_19_img_1.jpg How many LSPs are required in total between Metro A and Metro B if 100 hierarchical VPLS services are deployed across the two metro networks?

Accepted Answer

D

Explanation: Hierarchical VPLS (H-VPLS) is designed for scalability by multiplexing multiple services over a single transport tunnel. In this scenario, all 100 VPLS services between Metro A and Metro B are transported over a single Service Distribution Path (SDP) established between the hub-PE routers of each respective metro network. In an MPLS core, an SDP uses Label Switched Paths (LSPs) for transport. Since LSPs are inherently unidirectional, two LSPs are required to establish a bidirectional communication path between the two hub-PEs. One LSP is needed for the Metro A to Metro B direction, and a second LSP is needed for the Metro B to Metro A direction. These two LSPs form the transport tunnel for the single SDP carrying all 100 services.

Question 5

What is the MTU impact on the SDP path-mtu if fast reroute facilities-mode is implemented on the LSP?

Accepted Answer

B

Explanation: When MPLS Fast Reroute (FRR) with facility backup is enabled on an LSP, the Point of Local Repair (PLR) pre-establishes a bypass tunnel to the Merge Point (MP). Upon a primary path failure, the PLR pushes one additional MPLS label onto the packet's label stack. This new label directs the packet through the bypass tunnel. This extra label adds 4 bytes of overhead to the packet size. To prevent fragmentation during a reroute event, the Service Distribution Path (SDP) using this LSP must account for this worst-case scenario. Therefore, the effective path MTU for the service is reduced by 4 bytes.

Question 6

What is the result of initiating an oam mac-ping to an unknown unicast MAC address in a VPLS instance?

Accepted Answer

B

Explanation: The oam mac-ping is a VPLS OAM tool used to verify MAC address reachability across the service. When initiated for a MAC address that is not present in the originating PE's Forwarding Database (FDB), the request is treated as an unknown unicast frame. Consequently, the PE floods the mac-ping request to all other PEs participating in the VPLS instance. Upon receiving the flooded request, each PE checks its own FDB. Only the PE that has learned the target MAC address on one of its local Service Access Points (SAPs) will generate and send a reply. Other PEs that receive the flooded request but do not have the MAC in their FDB will discard it.

Question 7

Which of the following is a true statement?

Accepted Answer

B

Explanation: In a dynamic network, a higher MAC address age-time causes learned entries to remain in the Forwarding Database (FDB) for a longer period. This slow removal of potentially stale entries, combined with the constant learning of new MACs, increases the total number of entries held in the FDB at any given time. To prevent the FDB from reaching its capacity—which would cause flooding for unlearned destinations—a larger fdb-table-size is required to accommodate the accumulation of both active and inactive entries. A lower age-time would have the opposite effect, clearing stale entries faster and thus reducing the required table size.

Question 8

If a management VPLS is administratively disabled what will be the status of the associated user VPLS SAPs?

Accepted Answer

B

Explanation: In a Hierarchical VPLS (H-VPLS) model, the management VPLS (M-VPLS) provides the core transport mesh for multiple user VPLS instances. The operational state of a user VPLS and its components, such as Service Access Points (SAPs), is directly dependent on the state of the M-VPLS to which it is bound. When a management VPLS is administratively disabled (shutdown), it becomes operationally down. This action severs the transport path for all associated user VPLS services. Consequently, the system brings down (disables/prunes) all SAPs on those user VPLS instances to prevent traffic from being accepted and subsequently dropped (black-holed), ensuring consistent state propagation to the customer edge.

Question 9

The operation of a VPLS can be best described by which of the following statements?

Accepted Answer

D

Explanation: Virtual Private LAN Service (VPLS) is designed to emulate an Ethernet LAN segment over a provider's IP/MPLS network. Its operation is analogous to a learning bridge or switch. 1. MAC-based Switching (C): At its core, VPLS makes forwarding decisions based on the destination MAC address in the customer's Ethernet frame. 2. Targeted Forwarding (A): Through MAC learning, each Provider Edge (PE) router builds a forwarding database (FDB). When a frame with a known destination MAC arrives, the PE forwards it directly over the specific Service Distribution Path (SDP) tunnel leading to the remote PE connected to that destination, rather than flooding it. 3. Flood Minimization (B): While flooding is necessary for broadcast, unknown unicast, and multicast (BUM) traffic, a key operational goal is to minimize it to conserve core network bandwidth. MAC learning directly supports this by enabling targeted forwarding for known unicast traffic. All three statements accurately describe fundamental aspects of VPLS operation.

Question 10

In IEEE 802.1ag, how are loops detected?

Accepted Answer

B

Explanation: In IEEE 802.1ag Connectivity Fault Management (CFM), a loop is detected when a Maintenance End Point (MEP) receives a CFM frame that it originally transmitted. The most common frame for this is the Continuity Check Message (CCM). Each MEP in a Maintenance Association periodically multicasts CCMs. If a loop exists within the service path, a MEP's own CCM will be forwarded back to itself. Upon receiving its own CCM, the MEP raises a loop fault alarm, indicating an unintended closed path in the network. This mechanism is specific to the configured Maintenance Domain and provides a deterministic method for fault detection.

Question 11

Click on the exhibit below. https://kxbjsyuhceggsyvxdkof.supabase.co/storage/v1/object/public/file-images/NOKIA_4A0-105/page_33_img_1.jpg Management VPLS 100 has been created for redundant spoke-SDP connections. User VPLSs 10 and 20 are using the same spoke-SDPs that are being managed by VPLS 100. Unexpected behavior has been reported. Based on the following output, what is the most likely reason for the unexpected behavior?

Accepted Answer

A

Explanation: The provided output is for the command show service id 100 base. The key field in this output is M-VPLS : False. This field explicitly indicates whether the VPLS is configured as a management VPLS. For user VPLSs to inherit the spoke-SDP state and benefit from redundant connections managed by another VPLS, that VPLS must be configured as a management VPLS (M-VPLS). Since the output shows this is False, VPLS 100 is a standard VPLS, and the intended management relationship with VPLS 10 and 20 cannot be established, leading to the reported unexpected behavior.

Question 12

Click on the exhibit below. https://kxbjsyuhceggsyvxdkof.supabase.co/storage/v1/object/public/file-images/NOKIA_4A0-105/page_34_img_1.jpg You have been requested to add load balancing across the redundant spoke-SDPs in the network shown. What further configuration is required? (Choose 2)

Accepted Answer

C, D

Explanation: Load-balancing can only occur when a VPLS has more than one active spoke-SDP toward the same far-end PE, and when the redundant-SDP group is told to distribute traffic instead of running in primary/stand-by mode. Step 1: create a second SDP between each PE pair (PE1-PE3 and PE2-PE4); the two SDPs become members of the same redundant-SDP group and give the hashing algorithm at least two egress choices. Step 2: under the associated management VPLS, enable load-balancing as well; otherwise the control traffic that synchronises MAC entries continues to use primary/backup semantics and prevents symmetric forwarding for data traffic.

Question 13

In Active/Standby pseudowires a failed pseudowire has recovered. Under what circumstances will the active pseudowire revert to the previously failed link?

Accepted Answer

C

Explanation: In Nokia's Service Router Operating System (SR OS), Active/Standby pseudowire redundancy uses a precedence value to determine the active path. The path with the lowest numerical precedence is preferred. The default behavior is revertive, meaning if the primary (more preferred) path fails and later recovers, traffic will automatically switch back to it. A path is designated as primary by assigning it the lowest possible precedence value, which is 0. The keyword primary is a direct alias for the precedence value 0. Therefore, the service will revert to the previously failed link if that link was configured as the primary path.

Question 14

If the command "disable-learning" has been added at the VPLS level, then MAC entries which have already been learned will not be aged.

Accepted Answer

False

Explanation: The disable-learning command, when configured at the VPLS service level on a Nokia Service Router, only prevents the learning of new source MAC addresses. It does not affect the aging process for MAC entries that are already present in the Forwarding Database (FDB). These existing, previously learned MAC entries will continue to be subject to the configured MAC aging timer and will be removed from the FDB if they are not refreshed by subsequent traffic before the timer expires.

Question 15

MC-LAG provides link and node protection from an MDU to 3 or more PE devices.

Accepted Answer

False

Explanation: The statement is incorrect. Multi-Chassis Link Aggregation (MC-LAG) is a resiliency feature designed to provide link and node-level protection by enabling a downstream device, such as an MDU, to connect to a pair (2) of upstream Provider Edge (PE) devices. These two PE nodes form a redundant group and appear as a single logical system to the MDU from a Link Aggregation Control Protocol (LACP) perspective. The fundamental architecture of MC-LAG is based on a two-chassis system and does not support extending a single MC-LAG group to three or more PE devices.

Free Nokia 4A0-105 Actual Exam Questions