Nokia 4A0-100 Exam Dumps

In the diagram:

R2 and R4 are both within AS 65540, which indicates that they are in the same Autonomous System.

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

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

OSPF or IS-IS (both interior gateway protocols -- IGPs)

Static routing is also valid between any two routers if manually configured

eBGP is invalid between routers in the same AS.

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

Therefore, the correct answer is: D. eBGP

Nokia IP Routing Fundamentals -- BGP vs IGP

Nokia SRA Guide -- AS Concepts and Protocol Suitability

RFC 4271 -- BGP Specification

When a router forwards a packet, it performs the following operations:

Looks up the destination IP address in the routing table to determine the next hop or egress interface.

Uses the ARP table to resolve the MAC address of the next-hop IP.

Option A is incorrect -- source IP is not used for route lookup.

Option C is incorrect -- routers don't resolve the source MAC.

Option D is partially true, but routing begins with the routing table, making B the most accurate.

Nokia IP Fundamentals Study Guide -- Chapter: ''IP Packet Forwarding''

RFC 1812 -- Requirements for IP Routers

Nokia MPLS Fundamentals Guide -- Chapter: ''Label Operations (Push, Swap, Pop)''

Nokia SRA Study Guide -- Ingress/Egress LER roles in MPLS

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.

Nokia MPLS and Services Guide -- Core vs Edge Router Roles

Nokia SRA Study Guide -- 'PE and P Devices in MPLS'

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.

Nokia IP Networking Fundamentals Study Guide -- Chapter: 'Layer 2 Technologies'

IEEE 802.1D Standard -- Spanning Tree Protocol Overview