Free 4A0-104 Practice Test

In Nokia SR OS terminology a service can be local—both Service Access Points (SAPs) reside on the same node and traffic never leaves the chassis—or distributed, where at least one endpoint is reached through an MPLS pseudowire or service tunnel across the network.

N/A – single true/false statement.

1. Nokia “SR OS Service Architecture Guide”, Release 22.5.R1, Sec. 2.3 “Local vs. Distributed Services”, pp. 37-38.

2. Stanford CS244 “Advanced Networking”, 2021 lecture notes, p. 18: discusses local switching of SAPs vs. distributed VPNs in carrier Ethernet.

3. Nokia NRS II course “Services Architecture”, Module 2, slide 22: defines local-service and distributed-service distinction.

On Nokia SR OS PE routers, when an Ethernet frame is accepted on a SAP that belongs to a Layer-2 VPN (VPWS, VPLS, etc.), the ingress line-card removes and verifies the Ethernet Frame Check Sequence (FCS). The frame is transported across the MPLS/GRE core without the original FCS, and a new FCS is recalculated and appended on egress before the packet is delivered to the customer interface.

The only alternative to the given statement is that the FCS is transported end-to-end unchanged; Nokia documentation explicitly states that this is not the case, so choosing “False” would contradict the vendor’s specified behaviour.

1. Nokia (Alcatel-Lucent) 7750 SR OS Services Guide, R20.7, “Ethernet Frame Handling”, p. 372, para 2: “The ingress line card strips and verifies the FCS. On egress, a new FCS is generated and appended.”

2. Nokia 7750 SR OS Layer 2 Services Guide, R20.7, Sec. 4.1.1.2 “Frame Processing”.

In Nokia's Service Router Operating System (SR OS), both transport tunnels (like MPLS LSPs) and service tunnels (Service Distribution Paths or SDPs) are unidirectional. To establish a bidirectional communication path for a service between two routers, two separate unidirectional tunnels must be configured—one for each direction. For example, an SDP must be configured from PE1 to PE2, and a second SDP must be configured from PE2 to PE1. Configuration is required on both endpoint routers.

A. (The statement is True) This is incorrect because tunnels in SR OS are fundamentally unidirectional constructs, requiring explicit configuration for each direction of traffic flow.

1. Nokia 7750 SR OS, Services Architecture Guide, Release 21.10.R1, Chapter: Service Distribution Paths (SDPs). The guide states, "An SDP is a unidirectional service tunnel between two 7750 SR routers."

2. Nokia 7750 SR OS, MPLS Guide, Release 21.10.R1, Chapter: Label Distribution Protocol (LDP). The guide describes LSPs as unidirectional paths from an ingress LER to an egress LER.

The association of a service to a customer is a fundamental property established when the service is created. The customer ID cannot be modified after the service context has been created. To change the customer association for a service, the existing service must be deleted and then recreated with the new, correct customer ID.

The statement "True" is incorrect because the customer command within a service context is a create-time parameter and is not modifiable on an active or existing service. This is a design principle in SR OS to ensure service integrity and consistent accounting.

Nokia 7450 ESS, 7750 SR, 7950 XRS, and VSR Services Overview Guide, Release 22.10.R1, Part Number: 3HE 18378 AAAD TQZZA, Section: "Customers". This section describes the creation of customers and their association with services, implying the static nature of the binding post-creation. The command structure config>service>vpls customer create shows customer ID is part of the creation process.

Nokia 4A0-104 Course Material, Module 2: Services, Topic: Service Provisioning Workflow. The workflow explicitly shows that customer creation precedes service creation and that the service is created under a specific customer ID.

On a dot1q-encapsulated access port, any frame that arrives with VLAN tag 0 (priority-tagged) or arrives untagged is associated with the predefined null SAP. The null SAP discards the traffic unless it is explicitly bound to a service.

B. (False) Frames with VLAN 0/untagged are not matched to regular SAPs; they map to the null SAP as documented.

1. Nokia 7750 SR OS Service Configuration Guide, 23.10.R1, “SAP Encapsulation – dot1q”, p. 421, para 3.

2. IEEE 802.1Q-2018, sec. 12.13.2 – definition of priority-tagged (VLAN 0) frames and provider handling.

Within Nokia service routers, “customer” identifies the administrative owner of a set of services, while “service” defines the actual connectivity construct (IES, VPLS, VPWS, etc.). The two terms are distinct and not interchangeable.

A – Treating the two terms as synonymous would ignore the administrative separation between customer context and service instance.

1. Nokia 7750 SR OS Services Guide, 22.10.R1, §4.1 “Customer and Service Contexts”, pp. 87-88.

2. Nokia 4A0-104 Student Courseware, Module 2, Slide 9, “Customer vs Service Naming”.

In the Nokia SR OS, a transport tunnel is implemented using a Service Distribution Path (SDP). When configuring an SDP, the operator must specify the encapsulation type to be used for tunneling service traffic across the provider core network. The SR OS supports multiple encapsulation types for SDPs, with the two primary options being MPLS and Generic Routing Encapsulation (GRE). This allows flexibility in how Layer 2 and Layer 3 VPN services are transported over the IP/MPLS backbone.

B. (The statement is False) This is incorrect because both MPLS and GRE are explicitly supported and commonly used encapsulation types for SDPs in Nokia's service architecture.

1. Nokia 7750 SR OS, Services Architecture Guide, Release 21.10.R1, Chapter: Service Distribution Paths (SDPs), Section: SDP Encapsulation Types. This section explicitly lists "GRE" and "MPLS" as supported encapsulation types.

2. Nokia 4A0-104 Course Material, Nokia Multiprotocol Label Switching, Module 6: Virtual Private Network Services. The module details the configuration of SDPs and shows the options for encap-type including gre and mpls.

In Nokia's Service Router Operating System (SR OS), when configuring a VPLS service, a mesh Service Distribution Path (SDP) is used to create a full mesh of pseudowires between all Provider Edge (PE) routers in the service. Each pseudowire requires a unique Virtual Circuit Identifier (VC-ID) for signaling with its peer. To simplify configuration, if the network administrator does not explicitly define a vc-id for the mesh-sdp, the system automatically and by default uses the VPLS service-id as the vc-id.

This is a True/False question. The statement is factually correct based on the default behavior of the SR OS, so "False" would be incorrect.

1. Nokia 7750 SR OS Services Configuration Guide, Release 21.10.R1, VPLS Command Reference. In the section describing the mesh-sdp command, the parameter vc-id is detailed. The documentation states: "If the vc-id is not specified, the service-id of the VPLS is used as the vc-id."

2. Nokia Virtual Private LAN Service (VPLS) Fundamentals, Student Guide, WB1033-1-001. Module 3: VPLS Configuration. This courseware explains that the vc-id must match between PEs for the pseudowire to be established and notes that its default value is inherited from the service ID.

The statement is true. The fundamental purpose of dot1q encapsulation on a Service Access Point (SAP) is to use the IEEE 802.1Q VLAN tag as the service delimiter. When a tagged Ethernet frame arrives at a physical port, the router inspects the VLAN ID in the frame's header. If this VLAN ID matches the value configured for a specific SAP on that port (e.g., sap 1/1/1:100), the frame is accepted and processed by the service associated with that SAP. Frames with VLAN tags that do not match any configured SAP on the port are discarded.

This is a true/false question. The statement accurately describes the behavior of a dot1q SAP, so "False" would be incorrect. This mechanism is essential for multiplexing multiple Layer 2 services on a single physical interface.

1. Nokia 7750 SR OS Services Guide, Release 21.10.R1, "Service Access Points (SAPs)" section. The documentation states: "For dot1q and qinq encapsulations, the VLAN tags are used to identify the SAP. When a packet is received on a port, the VLAN tag determines which SAP the packet belongs to." This directly confirms the statement.

The statement is false. An Epipe is a Nokia implementation of an Ethernet Virtual Private Wire Service (VPWS). While Ethernet ports are a common access type for Epipes, they are not the only type. SAPs for Epipe services can also be configured on other interface types that can carry Ethernet frames, such as Packet over SONET/SDH (POS) ports or within channels on SONET/SDH and TDM interfaces. The service is designed to be flexible regarding the physical access medium, as long as Ethernet frames can be transported over it.

This is a True/False question. The statement is false because Nokia's Epipe service implementation is not restricted solely to physical Ethernet ports.

1. Nokia 7750 SR OS Services Architecture Guide, Release 21.10.R1, "Epipe Service Overview" section. The documentation states, "An Epipe service is a Layer 2 point-to-point service. The 7750 SR supports Epipe services over Ethernet, SONET/SDH, and TDM access circuits."

2. Nokia 7750 SR OS Layer 2 Services and EVPN Guide, Release 21.10.R1, "Epipe SAPs" section. This guide provides configuration examples and details for creating Epipe SAPs on various port types, including port-id for Ethernet and sonet-sdh or tdm channel-groups, explicitly refuting the claim that only Ethernet ports are supported.