Spanning Tree Protocol (STP) is used specifically in Ethernet Layer 2 networks to prevent loops

caused by redundant paths.

STP detects loops and blocks one or more redundant paths to ensure there is a loop-free topology in

a bridged network.

STP dynamically recalculates the topology if 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 B is correct, as STP is explicitly designed for Layer 2 Ethernet networks with

redundant paths.

Reference:

Nokia IP Networking Fundamentals Study Guide – Chapter: "Layer 2 Technologies"

IEEE 802.1D Standard – Spanning Tree Protocol Overview

A broadcast IP address is used to send a message to all devices on a specific IP subnet. This address is

the highest 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 B refers to multicast, not broadcast.

Option C might refer to anycast, which is different.

Option D describes a unicast address.

Reference:

Nokia IP Fundamentals Study Guide – Chapter: "IP Addressing and Broadcast Communication"

RFC 919 – Broadcasting Internet Datagrams

OSPF (Open Shortest Path First) is a Link-State protocol that uses:

Cost (based on bandwidth) as its metric.

Dijkstra’s algorithm to compute shortest path trees.

Supports hierarchical routing with areas (e.g., Area 0 as backbone).

Routers exchange LSAs, not full routing tables.

Option D is FALSE – OSPF does not use hop-count. That’s a RIP (Distance Vector) feature.

Reference:

Nokia IP Routing Guide – Section: “OSPF Operation and Area Design”

RFC 2328 – OSPFv2 Protocol Specification

In a typical MPLS/VPN service architecture:

PE (Provider Edge) router: Directly connects to the customer edge (CE) device.

P (Provider) router: Only forwards MPLS-labeled packets, does not touch customer routes.

LSR (Label Switch Router): General term, can be either PE or P depending on placement.

Correct Answer: A – PE

Explanation:

It interfaces with CE devices and runs customer routing protocols (e.g., OSPF, BGP).

Reference:

Nokia MPLS and VPN Guide – PE vs P Role

Nokia SRA Study Guide – PE-CE and Core Router Design

A P router (Provider router) is located in the core of the service provider’s network. Its functions

include:

Forwarding MPLS-labeled packets between PE routers.

Not interacting directly with customer routes or routing instances.

Having no knowledge of VPN routing or customer-specific services.

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

Reference:

Nokia MPLS and Services Guide – Core vs Edge Router Roles

Nokia SRA Study Guide – "PE and P Devices in MPLS"

Tier 1 ISPs: Have global reachability and exchange traffic via peering. They do not pay for transit.

Tier 2 ISPs: Purchase transit services from Tier 1 and provide transit to Tier 3 or other Tier 2 ISPs.

Tier 3 ISPs: Provide last-mile connectivity to end users and do not provide transit services.

Option A is correct – Tier 1 and Tier 2 provide transit services.

Reference:

Nokia IP Networks and Services Guide – ISP Tiering

Global Internet Infrastructure Overview

Reference:

Nokia IP Fundamentals Guide – Chapter: “Subnetting and Address Calculations”

Subnet Math – RFC 950 principles

:

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

In Nokia SR OS:

A physical interface refers to a physical port on the router (e.g., port 1/1/1).

It can be configured with IP addresses, associated with services (e.g., IES, VPRN), and connects to

other routers or customer devices.

System and loopback interfaces are logical interfaces, not physical.

Option D is FALSE, because a physical interface cannot be of type "system" or "loopback" — those are

virtual/logical interfaces in the Nokia router architecture.

Reference:

Nokia SRA Study Guide – Chapter: “Interfaces and Ports”

Nokia SR OS Interface Configuration Guide