Free and Premium Nokia 4A0-100 Dumps Questions Answers

A/26 subnetmeans26 bits for the networkand6 bits for host addressing(32 - 26 = 6):

2⁶ = 64 total addresses per subnet

64 - 2 =62 usable host addresses per subnet

/24 to /26 increases subnet bits by 2, so:

2² =4 subnetsfrom one /24

But the question asks aboutusing /26, which means:

From /24 → each /26 block gives64 IPs

So you get4 subnets total

But the options must be interpreted carefully!

→Let's calculate again properly:

/26 = 64 addresses per subnet (2⁶)

Usable hosts per subnet = 64 - 2 = 62

Number of subnets in /24 when divided by /26 = 2^(26 - 24) = 4 subnets

So correct result is:

4 subnets, 62 hosts per subnet→Correct Answer: C

However,Option D says 8 subnets, 30 hosts per subnet, which actually matches a/27 mask, not /26.

Final Correct Answer:C

VPLS (Virtual Private LAN Service)is aLayer 2 VPN servicethat emulates abridged Ethernet LANacross an MPLS/IP network.

Learns MAC addresses dynamically from:

SAPs (Service Access Points)

SDPs (Service Distribution Points)

Maintains aForwarding Database (FDB)per VPLS instance.

For unknown MAC destinations, a VPLSfloods the frameto all other sites – just like a regular Ethernet switch.

Option C is FALSE– VPLSdoes NOT discard unknown MACs; itfloodsthem.

Route summarization (a.k.a. supernetting)is the process ofcombining multiple contiguous subnetsinto asingle summarized route, which:

Reduces routing table entries

Enhances scalability and efficiency

Minimizes instability by localizing route changes

Option A is falsebecauseit describes subnetting, not summarization. Summarization works in theopposite direction– combining smaller routes into a larger one.

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.

Address summarization(also called route aggregation) is a technique used in IP routing to combine several contiguous network prefixes into asingle summarized route.

This reduces the number of routes that need to be advertised and stored in routing tables, improvingscalability and performance.

Option A is correct– summarization replaces many specific routes with a single aggregated route.

Option Brefers to best path selection (not summarization).

Option Cis incorrect; duplicate advertisements are still processed and filtered based on metrics.

Option Dis unrelated to summarization; directly connected routes are always advertised unless specifically filtered.

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.

AP router (Provider router)is locatedin the core of the service provider’s network. Its functions include:

ForwardingMPLS-labeled packetsbetweenPE routers.

Not interacting directly with customer routes or routing instances.

Having no knowledge ofVPN routing or customer-specific services.

Option C is correct– P routers sit in theMPLS core, isolated from customer edge.

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.

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.

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

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).

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