4A0-100 Practice Questions

The system interface in Nokia SR OS is a loopback-style logical interface that represents the router

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 is type loopback ✔

It exists by default ✔

If router ID is unset, it uses the system IP address ✔

But the IP address on the system interface does not need to be /32 ❌

It can have other prefix lengths, especially in service provider scenarios.

Thus, Option B is FALSE.

Reference:

Nokia SRA Study Guide – Chapter: "System Interface and Loopbacks"

Nokia SR OS Fundamentals Guide – System IP Configuration Section

BGP (Border Gateway Protocol) uses a multi-step decision process to select the best route among

multiple paths. It does not 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 evaluates multiple attributes for route selection.

Reference:

Nokia IP Routing Fundamentals – BGP Route Selection

RFC 4271 – BGP Decision Process

The Nokia 7750 SR architecture separates its operations into control plane and data plane functions.

The Data Plane includes 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.

The Control Plane includes the CPM (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 thus not part of the data plane.

Reference:

Nokia SRA Study Guide, Chapter: "System Architecture – 7750 SR Components"

Nokia IP Networks and Services Fundamentals – Section: Control and Data Plane Functions in SR

Architecture

VLAN Stacking, also known as Q-in-Q tunneling, is a technology that allows multiple customers to

use overlapping VLAN IDs while being transported over a shared 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 a C-VLAN is encapsulated with an additional outer

S-VLAN tag.

This way, multiple customers can use the same C-VLAN ID, but remain isolated by the unique S-VLAN

assigned 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.

Reference:

Nokia Service Architecture and VPNs Study Guide – Section: “Q-in-Q VLAN Stacking”

IEEE 802.1ad Standard – Provider Bridges (Q-in-Q)

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 altered as 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.​

Reference: Nokia IP Networks and Services Study Guide – Chapter on VPN Services​

Route summarization (a.k.a. supernetting) is the process of combining multiple contiguous subnets

into a single summarized route, which:

Reduces routing table entries

Enhances scalability and efficiency

Minimizes instability by localizing route changes

Option A is false because it describes subnetting, not summarization. Summarization works in the

opposite direction – combining smaller routes into a larger one.

Reference:

Nokia IP Routing Guide – Chapter: “Route Summarization Techniques”

Cisco CCNA – IP Routing Concepts

A VPRN (Virtual Private Routed Network) provides a Layer 3 VPN service over a service provider’s

network.

Each customer site connects to a PE router.

Sites are connected via a routed network using separate routing instances.

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

Option C is correct – VPRN provides routed connectivity between sites.

Reference:

Nokia Service Routing Guide – Chapter: VPRN

Nokia SRA Guide – Service Types and Operation

The Internet Assigned Numbers Authority (IANA) is responsible for managing the global IP address

pool, along with:

Allocating blocks of IP addresses to Regional Internet Registries (RIRs) such as ARIN (North America),

RIPE NCC (Europe), APNIC (Asia-Pacific), etc.

Managing autonomous system numbers (ASNs).

Overseeing DNS root zones and protocol parameters.

IANA does not assign IPs directly to enterprises or individuals — those tasks are delegated to RIRs

and ISPs.

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

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

Option C is correct – IANA manages the global IP address allocation hierarchy.

Reference:

IANA official site: https://www.iana.org

Nokia IP Fundamentals – IP Address Management and Allocation Hierarchy

A /31 subnet in IPv4 provides exactly two IP addresses (e.g., 192.168.1.0/31 → usable: 192.168.1.0

and 192.168.1.1). Traditionally, these would represent a network address and a broadcast address,

but RFC 3021 redefines /31 subnets for point-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's ideal for point-to-point links, saving address space.

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

Reference:

Nokia IP Fundamentals Guide – Subnetting Techniques

RFC 3021 – "Using 31-Bit Prefixes on IPv4 Point-to-Point Links"

A MAC address (Media Access Control address) is a 48-bit identifier typically expressed in six groups

of two hexadecimal digits (e.g., 00-20-60-CE-2B-28). It consists of two key parts:

OUI (Organizationally Unique Identifier) – The first 24 bits (or first 3 octets, e.g., 00-20-60) are

assigned by the IEEE to hardware manufacturers. This identifies the vendor or manufacturer.

Device Identifier (NIC Specific) – The remaining 24 bits (e.g., CE-2B-28) are assigned uniquely by the

vendor to each device/interface.

So in the address 00-20-60-CE-2B-28:

00-20-60 is the OUI

CE-2B-28 is the device-specific portion

Thus, the correct answer is D. 00-20-60.

Reference:

IEEE MAC Address Standard (IEEE 802)

Nokia IP Networking Fundamentals Study Guide – Chapter: "Ethernet Addressing"