Free Nokia 4A0-100 Practice Exam with Questions & Answers

Tier 1 ISPs: Haveglobal reachabilityand exchange traffic via peering. Theydo not payfor transit.

Tier 2 ISPs: Purchasetransit services from Tier 1and provide transit to Tier 3 or other Tier 2 ISPs.

Tier 3 ISPs: Providelast-mileconnectivity to end users and donot provide transit services.

Option A is correct– Tier 1 and Tier 2provide transit services.

Astatic routeis a manually configured route added by a network administrator. It does not rely on dynamic routing protocols or metrics.

Itdoes not exchangeroutes with other routers (A – false).

It can be used bothwithin or across ASes(B – false).

Itdoes not use metricslike 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

VLAN Stacking, also known asQ-in-Q tunneling, is a technology that allowsmultiple customers to use overlapping VLAN IDswhile being transported over ashared service provider network.

Key Concepts:

Customer VLAN (C-VLAN):The VLAN used by the customer in their own network.

Service VLAN (S-VLAN):The VLAN used by the service provider to encapsulate the customer VLAN.

When VLAN stacking is applied:

A customer's Ethernet frame already tagged with aC-VLANisencapsulated with an additional outer S-VLAN tag.

This way,multiple customers can use the same C-VLAN ID, but remain isolated by theunique S-VLANassigned to them by the service provider.

Why Other Options Are Incorrect:

A. VLAN Trunking:Used to carry multiple VLANs over a single physical link but doesn’t allow reuse of VLAN IDs across customers.

C. VLAN Tagging:Refers to the general process of adding a VLAN tag; it doesn't provide the isolation needed across shared infrastructure.

D. VLAN Routing:Refers to Layer 3 routing between VLANs, not to ID reuse or transport over a shared provider backbone.

TheDHCP client/server exchangefollows a specific four-step sequence known asDORA:

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 ensuresdynamic IP configurationand is used in enterprise and home networks.

TheIngress Label Edge Router (LER)is the first router that:

Receives an unlabeled IP packet.

Applies an MPLS labelbased on its forwarding decision.

Forwards it into theMPLS 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.

BGP (Border Gateway Protocol)uses amulti-step decision processto select the best route among multiple paths. It doesnot 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 evaluatesmultiple attributesfor route selection.

In Nokia SR OS, theMD-CLIprovides multiple configuration edit modes to allow different types of user interaction with the configuration system:

Private modeallows multiple users to create individual configuration candidates, which are then merged with the global candidate during commit.

Global modeenables multiple users to edit the same candidate configuration at the same time, with a shared commit session.

Read-only modeallows the user to view the configuration without making changes.

Exclusive moderestricts access to the global candidate configuration such thatonly one user at a timecan enter and make changes. This prevents conflicts and is useful in environments where strict control over configuration changes is necessary.

Therefore, the correct answer isExclusive mode, as itexclusively locks access to the global candidatefor a single user.

VPWS (Virtual Private Wire Service)on Nokia 7750 SR:

Emulates aLayer 2 point-to-pointconnection.

Does not require MAC learning, unlike VPLS.

UsesMPLS encapsulation,not IP datagramsfor transport.

Option D is FALSE– VPWS usesMPLS labels, not IP encapsulation.

In Nokia SR OS:

Aphysical interfacerefers to a physical port on the router (e.g., port 1/1/1).

It can be configured withIP addresses, associated with services (e.g., IES, VPRN), and connects to other routers or customer devices.

Systemandloopbackinterfaces arelogical interfaces, not physical.

Option D is FALSE, because a physical interfacecannotbe of type "system" or "loopback" — those arevirtual/logicalinterfaces in the Nokia router architecture.

Spanning Tree Protocol (STP)is used specifically inEthernet Layer 2 networkstoprevent loopscaused byredundant paths.

STPdetects loops and blocks one or more redundant pathsto ensure there is aloop-free topologyin a bridged network.

STP dynamicallyrecalculates the topologyif a link fails, reactivating previously blocked paths.

Explanation of other options:

A. MPLS with LSPs:MPLS uses its own mechanisms for path management, such as RSVP or Segment Routing. STP is not applicable here.

C. OSPF with ECMP (Equal-Cost Multi-Path):OSPF is a Layer 3 protocol that inherently supports multiple paths without loops; STP is not involved.

D. eBGP (Exterior Border Gateway Protocol):Operates at Layer 3 for inter-AS communication; STP is not used in BGP routing.

Therefore,Option Bis correct, as STP is explicitly designed forLayer 2 Ethernet networkswithredundant paths.