4A0-100 Nokia IP Networksand Services Fundamentals Question and Answers

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.

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

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.

In the diagram:

R2 and R4 areboth within AS 65540, which indicates that they are in thesame Autonomous System.

eBGP (External Border Gateway Protocol)is designed for routingbetween different ASes(inter-AS routing).

Since R2 and R4 are in thesame AS, you would use:

OSPForIS-IS(both interior gateway protocols – IGPs)✔

Static routingis also valid between any two routers if manually configured✔

eBGP❌is invalid between routersin the same AS.

âž¡The correct protocol in that case would beiBGP (internal BGP)if BGP were to be used within the AS.

Therefore, the correct answer is: D. eBGP

In MPLS architecture, theIngress LER (Label Edge Router)is responsible for:

Pushing labelsonto unlabeled packets and injecting them into the MPLS domain.

Acting as thestarting point of the Label Switched Path (LSP).

From the diagram:

R1is thestarting point (Ingress LER)for both LSP A and LSP B.

R4is theEgress LER, which wouldpopthe labels at the end of the LSP.

So,R1 is responsible for label push (imposing)at the start of both LSPs.

Option A is correct– R1 pushes labels for both LSP A and LSP B.

Option Bis incorrect – R4 is an egress router, not ingress.

Option C/Dare incorrect – the LSPs both start at R1.

ICMP (Internet Control Message Protocol)is used for network diagnostics and error messaging. Key uses include:

Ping (Echo Request/Reply)– tests end-to-end connectivity✔

Traceroute– uses ICMP time exceeded messages to identify hops✔

Error reporting– returns various error types with differentcodes✔

However,ICMP does not re-route traffic. If a destination is unreachable, ICMP reports the error back to the sender; it doesn’t instruct routers to re-route.

Option D is FALSE– ICMPdoes not perform routing.

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.

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.

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.