4A0-100 Exam Dumps - Nokia SRC Certification Questions and Answers

A Virtual Private Network (VPN) is designed to provide secure and private communication over a shared or public infrastructure. Key characteristics of VPNs include:​

Traffic Isolation:Each customer's traffic is kept separate from others, ensuring privacy and security.​

Shared Infrastructure:Service providers can support multiple VPNs over the same physical infrastructure, optimizing resource utilization.​

Customization:VPNs can be tailored to meet the specific requirements of individual customers, including security policies, routing, and quality of service.​

However,customer data is not alteredas it traverses a VPN. Instead, VPNs employ encryption and tunneling protocols to protect data integrity and confidentiality during transmission. The primary goal is to ensure that data remains unchanged and secure from end to end.​

TheShortest Path Tree (SPT)is calculated byLink-State routing protocolslikeOSPFandIS-ISusing:

Acomplete map of the network topology.

Each router uses algorithms likeDijkstra’sto compute the shortest paths to all destinations.

Option C is correct– fullnetwork topologyis used.

Option Arefers to Distance Vector methods.

Option BandDare results of topology analysis but not the input used.

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.

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.

Abroadcast IP addressis used tosend a message to all deviceson a specific IP subnet. This address is thehighest address in the subnet(i.e., all host bits set to 1).

Example: In 192.168.1.0/24 → broadcast is 192.168.1.255.

It is used for purposes like ARP requests or DHCP discovery.

Option A is correct– refers to all hosts in a subnet.

Option Brefers tomulticast, not broadcast.

Option Cmight refer toanycast, which is different.

Option Ddescribes aunicastaddress.

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.

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.

AVirtual Local Area Network (VLAN)is a logical separation of devices atLayer 2, even ifthose devices are connected to the same physical switch. Each VLAN forms itsown broadcast domain, and traffic cannot cross from one VLAN to anotherwithout Layer 3 routing.

Option Ais incorrect – devices on the same switch but in different VLANs still cannot communicate directly.

Option Bis incorrect – VLANs explicitlycreate separate broadcast domains.

Option Dis technically incorrect – communication is possible with the right setup.

Option Cis correct – to enable communication between different VLANs, arouteror aLayer 3 switchwith inter-VLAN routing capability is required.

This process is calledinter-VLAN routing, and it's a fundamental task in enterprise networks using VLANs.

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.

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.