4A0-100 Exam Questions & Answers

Link-State routing protocols (e.g., OSPF, IS-IS) operate by:

Each router flooding link-state advertisements (LSAs) throughout the network.

Every router constructs a complete map of the network topology.

Then each router runs the SPF algorithm to compute optimal paths.

Option C is correct -- routers know the entire network topology.

Option A is Distance Vector behavior (e.g., RIP).

Option B is not efficient or accurate for Link-State.

Option D -- hop-count is used in Distance Vector (e.g., RIP).

Nokia SRA Study Guide -- Chapter: ''OSPF and IS-IS Concepts''

RFC 2328 -- OSPF Link-State Overview

Comprehensive and Detailed Explanation From Exact Extract:

In the Nokia SR OS CLI, specifically in both classic CLI and MD-CLI, the '?' key is used to display a list of all possible command options at a given point in the CLI, along with a brief description of each option.

This functionality helps the user in command discovery and reduces the chances of syntactical errors by showing only valid options.

The 'Tab' key, while helpful, is primarily used for auto-completion and not for displaying detailed descriptions.

'Space bar' is used for command continuation, and 'Return' executes the command or moves to the next line.

Correct usage example in classic CLI:

*A:SR1>config>router>interface# ?

- Shows all the valid commands and parameters under interface

Nokia SRA Study Guide -- Chapter: 'CLI Fundamentals'

Nokia SR OS Fundamentals Guide -- Section: 'Using the CLI Help System'

A static route is a manually configured route added by a network administrator. It does not rely on dynamic routing protocols or metrics.

It does not exchange routes with other routers (A -- false).

It can be used both within or across ASes (B -- false).

It does not use metrics like hop count (C -- false).

Option D is correct -- the operator explicitly defines the next-hop IP or egress interface manually.

Static routes are often used for:

Default routing

Backup routing

Simple or small networks

Nokia IP Fundamentals -- Chapter: ''Static vs Dynamic Routing''

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.

Nokia IP Networks and Services Guide -- ISP Tiering

Global Internet Infrastructure Overview

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.

Nokia IP Fundamentals Guide -- Subnetting Techniques

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