GNS 3 and Oracle VirtualBox – Make Them Work Together. Use VM as Devices in GNS 3.

How do you create a LAN segment like this in GNS3?

  • It has two Ubuntu Virtual Machines
    • Connected to Oracle VirtualBox VMs
    • One Ubuntu/Linux acts as the DHCP Server
    • Another Ubuntu/Linux acts as the DHCP Client

Hints/Steps:

In Oracle VirtualBox, create two Ubuntu Machines (Virtual). These can be two new machines, or you can clone two VMs from one Parent Virtual Machine (in Oracle VirtualBox). Afterward, In GNS 3, from Edit->preferences -> VirtualBox configures two Virtual Machines pointing to Oracle VirtualBox VMs.

VMs in Oracle Virtual Box:

GNS 3: Edit-> Preferences

After you configure in Edit -> Preferences, you will see Ubuntu VMs in GNS3. Then you can use them in your GNS 3 projects as devices.

Java Design Patterns Simplified

From AI Tools/OpenAI/Internet

Here’s a short, copyright-free version suitable for Facebook or a blog post:


Java Design Patterns Simplified

Design patterns are proven solutions to common programming problems. They make code more reusable, flexible, and easier to maintain.

1️⃣ Creational Patterns – How objects are created.
Examples: Singleton, Factory, Builder, Prototype.

2️⃣ Structural Patterns – How objects are organized and related.
Examples: Adapter, Decorator, Facade, Proxy, Composite.

3️⃣ Behavioral Patterns – How objects interact and communicate.
Examples: Observer, Strategy, Command, State, Template Method.

💡 Tip: Using design patterns wisely can save time, reduce errors, and make your code cleaner and easier to understand.


Code Refactoring in Java EE

From AI Tools/OpenAI/Internet

Absolutely! Here’s a concise, copyright-free summary of Java EE code refactoring


Java EE Code Refactoring: Best Practices

Refactoring in Java EE helps improve code quality, maintainability, and performance without changing functionality. Here are some key practices:

1. General Refactoring

  • Remove duplicate code with helper methods or utility classes.
  • Break long methods into smaller, focused functions.
  • Use meaningful names for classes, methods, and variables.
  • Replace hard-coded values with constants or enums.
  • Encapsulate fields with getters/setters.

2. Refactoring Java EE Components

  • EJBs: Extract shared logic into stateless beans, use dependency injection instead of manual JNDI lookups.
  • JPA: Use DTOs instead of exposing entities, avoid N+1 queries, and consolidate repetitive validations with bean validation.
  • Servlets/JSPs: Keep Servlets thin; move business logic to service layers; use JSTL or custom tags for repetitive JSP code.
  • REST Services: Handle repeated request logic with filters/interceptors, use DTOs, and centralize exception handling.
  • CDI: Use @Inject to decouple components and define proper bean scopes.

3. Architecture & Design

  • Separate concerns with service, DAO, and controller layers.
  • Centralize exception handling and logging.
  • Move configuration values to properties files or environment variables.

4. Performance & Efficiency

  • Use connection pooling and caching.
  • Optimize lazy vs. eager loading in JPA.
  • Batch database operations when possible.

5. Testing & Maintainability

  • Write unit tests for services and DAOs.
  • Make code testable by avoiding static dependencies.
  • Use mocking frameworks for isolated component testing.

Summary:
Refactoring in Java EE focuses on separation of concerns, decoupling, eliminating duplication, optimizing persistence, centralizing logging and exceptions, and improving testability. Following these practices keeps enterprise applications clean, efficient, and easier to maintain.


BOOTP vs DHCP Protocol

From AI Tools/OpenAI/Internet

FeatureBOOTPDHCP
Full nameBootstrap ProtocolDynamic Host Configuration Protocol
Origin1980s, designed for diskless workstations1990s, developed as an extension of BOOTP
Address assignmentStatic (pre-configured per MAC address)Dynamic, automatic, and renewable
Lease conceptNo lease; addresses permanentUses timed leases with renewal mechanism
Configurable optionsLimited (IP, gateway, boot file)Extensive (IP, subnet mask, DNS, gateway, etc.)
Renewal supportNot supportedSupported through lease renewal
Common use todayRarely used, legacy environments onlyStandard in modern networks
TransportUDP ports 67 (server) and 68 (client)Same UDP ports as BOOTP

Implement DHCP Server in GNS 3: Experiment with DHCP Protocol with DHCP server and Clients

Experiment with the DHCP Protocol with a DHCP server and Clients

Tools Required:

  • GNS 3
  • VMWare Workstation Pro or Oracle VirtualBox
  • GNS VM
  • Wireshark

Steps in GNS 3:

  1. Create the LAN segment
  2. Configure a DHCP Server
  3. From PCs (clients) : request IP address from the DHCP server
  4. Check the DHCP requests/steps in the background
  5. Utilize Wireshark to check the packet/data/frame

LAN Segment to Implement

Steps to Create the LAN Segment

In GNS 3, create a projectBring the Devices 2 VPCs (PC1, PC2)One Switch One Router (c3725)It is not there by default in the device list
Use the connections option to connect them like the diagram above  

Turn on all routers and PCs

Commands in the Router:

First of all, go to command prompt or the console/web-console of the Router.

Or telnet such as

telnet 192.168.64.5 5000

Then issue these commands:

R1# enable                                            (Privileged EXEC mode)

R1# configure terminal

R1(Config)# interface fastethernet 0/0

R1(config-if)# ip add 192.168.1.1 255.255.255.0

R1(config-if)# no shutdown   (Activate)

R1(config-if)# exit

R1(config )#interface fastethernet 0/0

R1(config-if)# ip dhcp pool cyber   (create DHCP Pool)

R1(dhcp-config)# network 192.168.1.0 255.255.255.0

R1(dhcp-config)#default-router 192.168.1.1

R1(dhcp-config)# dns-server 8.8.8.8

R1(dhcp-config)# do wr   

R1(dhcp-config)# exit

Now, go to the console/web-console/telnet-from-cmd of the PCs such as PC1, or PC2.

telnet 192.168.64.5 5000

PC1>ip dhcp

DDORA: Discover Message (two times), Offer, Request, Acknowledge

Do the same for other PCs such as PC2

Then try the PING command from one PC to another

Download Network Application Software

Download GNS

https://www.gns3.com/software/download

GNS VM

https://www.gns3.com/software/download-vm

Ubuntu Desktop

https://ubuntu.com/download/desktop

Download WireShark

https://www.wireshark.org/download.html

DHCP Protocol: How it Works

Get Details from RFC: https://datatracker.ietf.org/doc/html/rfc2131

Ref: https://crnetpackets.com/2017/04/24/ipv4-basics-part-1-dhcp-dynamic-host-configuration-protocol/

On RRSP Over Contribution in Canada

On RRSP Over Contribution in Canada.

“Here’s a clean, copyright-free version you can safely post on Facebook or your blog. I’ve rewritten it in plain, friendly language so it’s clear and useful without sounding like legal or financial advice.

❓ How much can I contribute to my RRSP in Canada, and what happens if I go over?

In Canada, your RRSP contribution limit is based on:

  • 18% of your previous year’s earned income, up to the CRA’s annual maximum, plus
  • any unused contribution room carried forward from earlier years.

You can find your personal limit in your CRA My Account or on your Notice of Assessment.

❓ What if I over-contribute?

  • The CRA gives everyone a $2,000 lifetime cushion for over-contributions.
  • If you go over your limit by $2,000 or less, you won’t pay a penalty (though you can’t claim a tax deduction on that excess until new room opens).
  • If you go over by more than $2,000, you’ll face a 1% per month tax on the extra amount until it’s withdrawn or new room becomes available.

❓ What if I already went over once before, and later I’m within the limit again? Can I over-contribute again?

Yes — the $2,000 cushion is ongoing, not a “one-time pass.”

  • Example: You once went $1,500 over by mistake. Later, when you gained new contribution room, you were back under the limit.
  • In the future, you can again go up to $2,000 over, as long as you don’t exceed the cushion at any one point in time.

This means you could, for example, intentionally over-contribute $2,000 to invest in something like an ETF inside your RRSP. That’s allowed.

⚠️ Important notes

  • The $2,000 is not an “extra” deduction — it only becomes deductible once new RRSP room opens up.
  • Be careful not to go over the cushion, because CRA penalties are expensive and apply automatically.
  • Keep good records so you know exactly where you stand.

✅ In short: You can contribute up to your RRSP limit, and you have a permanent $2,000 safety buffer. Using that buffer again in the future is fine, but crossing above it triggers penalties.

“Perfect 👍 Here’s a short infographic-style summary version you can use for Facebook or your blog — very visual and easy to read.


📌 RRSP Contribution Rules in Canada

1️⃣ Your Limit

  • 18% of last year’s earned income
    • unused room carried forward
  • Check CRA My Account / Notice of Assessment

2️⃣ The $2,000 Cushion

  • You can go up to $2,000 over your limit without penalty
  • But you can’t deduct that excess until new room opens

3️⃣ If You Go Over the Cushion

  • More than $2,000 over → 1% tax per month on the extra
  • Penalties continue until you withdraw or gain new room

4️⃣ What If You Already Over-Contributed Before?

  • The cushion is permanent, not one-time
  • If you’re back within your limit later, you can use the cushion again
  • Example: You can intentionally over-contribute $2,000 to buy an ETF in your RRSP

Bottom line: Stay within your RRSP limit + $2,000 buffer. Going above that costs money.


Ref: AI Tools/AI Chat/OpenAI

CPI, Core CPI, and Inflation

Ref: AI/Chat/Internet

Sure — here’s a concise, copyright-free summary:


CPI (Consumer Price Index) measures how the average prices of a set basket of goods and services change over time. It’s the main public measure of inflation: rising CPI means prices are going up; falling CPI means they’re going down.

Core CPI is the same calculation but without food and energy prices, which can swing sharply due to temporary factors like weather or oil markets. This makes Core CPI a better gauge of long-term inflation trends.

In relation to inflation:

  • CPI shows the total price change felt by consumers.
  • Core CPI focuses on underlying, broad-based price changes.
  • If both rise, inflation is likely persistent; if CPI rises but Core CPI is stable, the price increase may be temporary.

If you want, I can also create a visual diagram showing CPI vs. Core CPI and how they connect to inflation trends.

Query Strings in C#

Here’s a complete, copyright-free guide to Query Strings in C# / ASP.NET, including definition, examples, use cases, limitations, performance, and security. You can freely copy-paste this on your blog or Facebook page.


🔗 Query String in C# ASP.NET – Complete Guide

📘 Definition

A query string is a part of the URL that carries data from one web page to another. It starts after a ? and consists of key-value pairs, separated by &.

In ASP.NET, query strings are commonly used to pass small amounts of data between pages.


🧾 Example of a Query String

https://example.com/profile.aspx?userId=123&lang=en
  • ?userId=123&lang=en is the query string.
  • userId and lang are keys, and 123, en are values.

🧪 How to Use Query Strings in ASP.NET

🔹 Send a Query String (Redirect with Data)

Response.Redirect("Profile.aspx?userId=123&lang=en");

🔹 Read a Query String

string userId = Request.QueryString["userId"];
string lang = Request.QueryString["lang"];

Always check for null:

if (Request.QueryString["userId"] != null)
{
    int userId = int.Parse(Request.QueryString["userId"]);
}

✅ Common Use Cases

Use CaseExample
Navigation between pagesPass user ID, category ID, or search terms
Bookmarkable URLsSave filter/search settings in URL
Third-party API or link sharingShare public resources with identifiers in the URL
TrackingAdd campaign IDs, referral sources in URLs

⚙️ Limitations of Query Strings

LimitationDescription
Length limitBrowsers limit URL length (commonly 2,000+ characters)
Visible to userAnyone can see the data in the URL bar
Not secureNever use query strings to send passwords or personal info
Easy to modifyUsers can change values manually, potentially breaking logic
Not suitable for large dataShould be used for small pieces of information only

🚀 Performance Impact

  • Minimal impact for small data.
  • Faster than storing in session or reading from a database for navigation logic.
  • Can increase server load if users manipulate URLs to test invalid values (requires validation).

🔐 Security Considerations

ConcernRecommendation
🔓 Data is exposedNever pass sensitive info like passwords, tokens, or IDs directly
🧪 Input tamperingAlways validate and sanitize query string values
🦠 XSS attack risksUse URL encoding and avoid rendering user input directly
🔒 Use HTTPSPrevents interception of query string in transit

✅ Example: Safe Value Handling

string name = Server.HtmlEncode(Request.QueryString["name"]);

📌 Summary Table

FeatureDescription
What is it?Part of URL carrying data in key=value format
Syntax?key1=value1&key2=value2
Stored Where?In browser URL (client side)
Size LimitAround 2000 characters (browser-dependent)
LifetimeUntil user navigates or refreshes
Secure?❌ No, unless encrypted or protected with HTTPS
Use CasesSearch filters, public IDs, navigation, analytics
Not Good ForSensitive, large, or private data

🧠 Pro Tips

  • Keep values short and URL-safe (use HttpUtility.UrlEncode() if needed).
  • Use session or POST data for more secure or larger data.
  • Combine with server-side validation to prevent misuse.

Would you like a code sample project, visual diagram, or a PDF cheat sheet on this topic? Let me know!