4A0-100 Nokia IP Networksand Services Fundamentals Questions and 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.

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

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.

AVPRN (Virtual Private Routed Network)provides aLayer 3 VPN serviceover a service provider’s network.

Each customer site connects to aPE router.

Sites are connected via arouted networkusingseparate routing instances.

Customer routers seerouted connectivity, as if connected to their own private WAN.

Option C is correct– VPRN providesrouted connectivitybetween sites.

Ahubis aphysical layer (Layer 1)networking device used to connect multiple Ethernet devices in a network. Unlike switches or routers, hubs donot inspect or process frame headers. Instead, they perform a simple task:

Receive a signal (electrical or optical) on one port

Replicate that signal identically to all other ports

This means the hubdoes not examine Layer 2 (MAC addresses) or Layer 3 (IP addresses)and doesnot perform intelligent forwarding. It merelybroadcasts all incoming traffic to every other connected device, often resulting inhigh collision domainsand poor efficiency.

Option Adescribes arepeater, not a hub.

Option Cdescribes aswitch(Layer 2 device).

Option Ddescribes arouter(Layer 3 device).

Option Bis correct: A hub does not inspect headers and replicates traffic blindly.

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.

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.

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.

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.