Notes, summaries, assignments, exams, and problems for Computers

1.  A network technician is configuring port Security on a LAN switch interface. The security policy requires host MAC Addresses to be learned dynamically, stored in the address table, and Saved to the switch running configuration. Which command does the technician Need to add to the following configuration to implement this Policy? Switch(config)# interface fa0/1 
   Switch(config-if)# switchport mode access 
   Switch(config-if)# switchport port-security

·Switch(config-if)# switchport port-security mac-address sticky

2. On which switch interface would an Administrator configure an IP address so that the switch can be managed Remotely?

·VLAN 1

3. Refer to the exhibit. Match the packets with Their destination IP address to the exiting interface on the router.

Understanding IGRP Protocol

What is IGRP?

IGRP is a Cisco-specific protocol developed in the mid-1980s.

IGRP Advantages Over RIP

IGRP calculates a composite metric from a set of route variables. It can be implemented on networks of up to 255 hops in diameter. Additional advantages include:

• Unequal-cost load sharing
• An update period three times longer than RIP's
• A more efficient update packet format

Unlike RIP, which uses UDP, the IGRP process is accessed directly from the IP layer as protocol 9.

IGRP Routing and Process Domains

Using domains allows isolating communications within one domain from others. IGRP uses two types: routing domains and process domains.

• Routing domains: Defined by Autonomous System (AS) boundaries and communicate via Exterior Gateway

OPENFLOW:

defines OpenFlow as the first standard communications interface defined between the control and forwarding layers of an SDN architecture. OpenFlow allows direct access to and manipulation of the forwarding plane of network devices such as switches and routers, both physical and virtual 

OPENFLOW CONFIG CONCEPTS

OF Capable Switch: Physical OF switch.  Can contain one or more OF logicalswitches.

OpenFlow Configuration Point: configurationservice

OF Controller: Controls logical switch via OFprotocol

Operational Context: OF logicalswitch

OF Queue: Queues of packets waiting forforwarding

OF Port: forwarding interface. May be physical orlogical.

OF Resource: ports, queues, certificates, flow tables and other  resources of OF capableswitches 

Discuss the advantages of address aggregation (summarization) with respect to routing table size, routing update exchange, and routing optimization?

Route aggregation and subnetting shrink the size of routing tables used by routers. Without CIDR, a router must maintain many individual entries for routes within the same network. CIDR guarantees more efficient routing and reduces the number of CPU cycles when updating a routing table. It also reduces router memory requirements.

What are the key characteristics or requirements that should be fulfilled by any routing protocol?

A routing protocol should guarantee loop-free paths, calculate multi-hop optimal paths, use simple or composite network metrics, be scalable, converge rapidly, use network resources... Continue reading "Advantages of Address Aggregation and Key Characteristics of Routing Protocols" »

Listas Ligadas em C++: Adicionar, Excluir, Buscar e Imprimir

Implementação básica de uma lista simplesmente ligada em C++, cobrindo as operações essenciais de manipulação de dados.

Configuração Inicial em C++

#include <iostream>
using namespace std;

Classe Node (Nó)

Define a estrutura fundamental de cada elemento da lista.

class Node {
    public:
        int value; // Pode ser implementado qualquer tipo de dados aqui.
        Node *next;
        
        Node () {
            next = NULL; // Construtor Padrão
        }
        
        Node (int _value) { // Construtor com Atribuição de Valor
            value = _value;
            next = NULL;
        }
};

Classe List (Lista Ligada)

Gerencia a coleção de nós e as operações... Continue reading "Implementação de Listas Ligadas em C++ (CRUD)" »

Computer System Essentials

Core Operating System Components

Kernel: The OS's Foundation

The operating system's core, a platform that allows other software to execute.

Shell: User Interaction Interface

The operating system's interface for users to interact with all computer elements.

Thread: A Running Program or Task

Any program or task that is currently running.

File System: Data Storage & Retrieval Protocol

A protocol that defines how files are stored and retrieved on disk drives, or by threads and programs.

Disk Formatting: Setting a File System

The process of setting a disk's file system.

Major Operating Systems and Their Focus

• Microsoft Windows: Focuses its operating system on security.
• Linux: Emphasizes customizability.
• Chrome OS: Centered on web

1. CalculatorInterface.java

The following code defines the Remote Interface for the calculator application.

import java.rmi.*;

public interface CalculatorInterface extends Remote {
    public int add(int num1, int num2) throws RemoteException;
    public int subtract(int num1, int num2) throws RemoteException;
    public int multiply(int num1, int num2) throws RemoteException;
    public int divide(int num1, int num2) throws RemoteException;
}

2. ServerCalculator.java

This class implements the CalculatorInterface and extends UnicastRemoteObject to handle remote calls.

import java.rmi.*;
import java.rmi.server.*;

public class ServerCalculator extends UnicastRemoteObject implements CalculatorInterface {
    public ServerCalculator() throws RemoteException

Set Cover to Efficient Recruiting

Input: Set U of elements, collection S₁, ..., S_m of subsets of U, integer k ≥ 0

Construct an instance of the Efficient Recruitment Problem:

• Sports are represented by U.
• Applicants are represented by {1, ..., m}.
• For every s ∈ U and 1 ≤ i ≤ m, M[s, i] = 'qualified' if s ∈ S_i and 'not qualified' otherwise.

Steps:

1. Call the oracle for Efficient Recruiting with input M and k.
2. Return the result (yes or no) of the previous call.

Vertex Cover and Hitting Set

Graph: G = (V, E)

• U = V(G)
• S_i = {u, v}, where (u, v) is an edge of G.

Vertex Cover ⇒ Hitting Set:

If C is a vertex cover for G of size k, then by definition, for every edge (u, v) in G, either u ∈ C or v ∈ C. Therefore, C is a solution for Hitting Set because... Continue reading "Efficient Recruiting and Algorithm Design: Set Cover, Hamiltonian Path, and Longest Increasing Subsequence" »

Dynamic Host Configuration Protocol (DHCP) Servers

What is a DHCP Server?

A DHCP Server is a network server that automatically provides and assigns IP addresses, default gateways, and other network parameters to client devices. It relies on the standard protocol known as Dynamic Host Configuration Protocol (DHCP) to respond to broadcast queries by clients.

Benefits of DHCP

A DHCP server automatically sends the required network parameters for clients to properly communicate on the network. Without it, the network administrator has to manually set up every client that joins the network, which can be cumbersome, especially in large networks. DHCP servers usually assign each client with a unique dynamic IP address, which changes when the client’s... Continue reading "Network Fundamentals: DHCP, Subnetting, and Transport Protocols" »

1. Independent Set to Vertex Cover Reduction

Input

A graph G and an integer k.

Reduction Steps

1. Call the black-box for Vertex Cover with the input graph G.
2. Provide n-k as the target size, where n is the number of nodes in G.
3. Return the result ('yes' or 'no') from the black-box call.

2. SAT to Independent Set Reduction

Input

A CNF formula F.

Reduction Steps

1. Construct a graph G where the nodes of G are the literals occurring in F (with possible repetitions).
2. Add the following edges to G:
   • An edge joining every pair of complementary literals.
   • An edge joining any two literals that occur in the same clause.
3. Call the black-box for Independent Set with input graph G and an integer k, where k is the number of clauses in F.
4. Return the result ('yes' or 'no') from the