Free Nokia 4A0-100 Exam Dumps June 2026

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.

Nokia Service Architecture and VPNs Study Guide -- Section: ''Q-in-Q VLAN Stacking''

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

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

A hub is a physical layer (Layer 1) networking device used to connect multiple Ethernet devices in a network. Unlike switches or routers, hubs do not 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 hub does not examine Layer 2 (MAC addresses) or Layer 3 (IP addresses) and does not perform intelligent forwarding. It merely broadcasts all incoming traffic to every other connected device, often resulting in high collision domains and poor efficiency.

Option A describes a repeater, not a hub.

Option C describes a switch (Layer 2 device).

Option D describes a router (Layer 3 device).

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

Nokia IP Networking Fundamentals Study Guide -- Chapter: 'Network Devices and OSI Model'

CompTIA Network+ and Cisco CCNA foundational guides (for universally accepted hardware behavior)

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.

Nokia SRA Study Guide -- Chapter: ''Interfaces and Ports''

Nokia SR OS Interface Configuration Guide