Nokia 4A0-100 Nokia IP Networksand Services Fundamentals Exam Practice Test

Thesystem interfacein Nokia SR OS is aloopback-style logical interfacethat represents therouter itself. It is used for:

Router ID assignment (if not manually set)

Source IP for control-plane protocols (OSPF, BGP)

Reachability testing

Important properties:

It istype loopback✔

Itexists by default✔

If router ID is unset, it uses thesystem IP address✔

Butthe IP address on the system interfacedoes not need to be /32❌

It can haveother prefix lengths, especially in service provider scenarios.

Thus, Option B is FALSE.

Link-State routing protocols(e.g.,OSPF,IS-IS) operate by:

Each routerflooding link-state advertisements (LSAs)throughout the network.

Every router constructs acomplete map of the network topology.

Then each router runs theSPF algorithmto compute optimal paths.

Option C is correct– routers know theentire network topology.

Option A isDistance Vector behavior(e.g., RIP).

Option B isnot efficient or accurate for Link-State.

Option D –hop-countis used inDistance Vector(e.g., RIP).

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.

TheInternet Assigned Numbers Authority (IANA)is responsible for managing theglobal IP address pool, along with:

Allocating blocks ofIP addresses to Regional Internet Registries (RIRs)such as ARIN (North America), RIPE NCC (Europe), APNIC (Asia-Pacific), etc.

Managingautonomous system numbers (ASNs).

OverseeingDNS root zonesand protocol parameters.

IANAdoes not assign IPs directly to enterprises or individuals— those tasks are delegated toRIRs and ISPs.

Option A & B:Enterprises and residential allocations are handled by ISPs or RIRs.

Option D:North American IPs are managed byARIN, not IANA.

Option C is correct– IANA manages theglobal IP address allocationhierarchy.

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.

A/31 subnetin IPv4 provides exactlytwo IP addresses(e.g., 192.168.1.0/31 → usable: 192.168.1.0 and 192.168.1.1). Traditionally, these would represent anetwork address and a broadcast address, butRFC 3021redefines /31 subnets forpoint-to-point links, such as router-to-router connections.

In a /31 subnet:

Broadcast address is not used.

Both IPs are treated as usable host addresses.

It'sideal for point-to-point links, saving address space.

This is widely supported andstandardized in Nokia IP and routing platforms.

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.

TheNokia 7750 SR architectureseparates its operations intocontrol planeanddata planefunctions.

TheData Planeincludes hardware components responsible for forwarding traffic at line rate. These components include:

MDA (Media Dependent Adapter)– interfaces with physical media.

IOM (Input/Output Module)– performs high-speed packet forwarding and processing.

XMA (eXpandable Media Adapter)– extends port capacity and media support.

TheControl Planeincludes theCPM (Control Processor Module), which is responsible for running routing protocols, managing configuration, system operations, and other control-related functions. The CPM does not participate in data forwarding and is thusnot part of the data plane.

A layered protocol stack is designed to simplify network communication by separating functionalities into distinct layers. Each layer has a defined role and communicates with the layers directly above and below it. The main benefits of this model include:

Simplified design and implementation: Developers can focus on one layer without needing to understand the entire system.

Flexibility: New protocols can be developed and inserted at specific layers without redesigning the whole stack.

Interoperability: Standard interfaces allow different systems and vendors to work together.

Isolation of functions: Errors and updates can be managed within one layer without impacting others.

However,reducing protocol overhead is not a primary goalof this model. In fact, the encapsulation and interaction between layers can sometimesintroduce extra overhead. This overhead is a trade-off accepted to gain the other benefits listed above.

Comprehensive and Detailed Explanation From Exact Extract:

In theNokia SR OS CLI, specifically in bothclassic CLIandMD-CLI, the"?" keyis used to display a list of all possible command options at a given point in the CLI, along with a brief description of each option.

This functionality helps the user in command discovery and reduces the chances of syntactical errors by showing only valid options.

The"Tab"key, while helpful, is primarily used forauto-completionand not for displaying detailed descriptions.

"Space bar"is used for command continuation, and"Return"executes the command or moves to the next line.

Correct usage example in classic CLI:

*A:SR1>config>router>interface# ?

- Shows all the valid commands and parameters under interface

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.

In a typical MPLS/VPN service architecture:

PE (Provider Edge) router: Directly connects to thecustomer edge (CE)device.

P (Provider) router: Only forwards MPLS-labeled packets, doesnot touch customer routes.

LSR (Label Switch Router): General term, can be either PE or P depending on placement.

Correct Answer: A – PE

Itinterfaces with CE devicesandruns customer routing protocols(e.g., OSPF, BGP).