Flowchart Symbols

Common Flowchart Symbols

• Flowchart shapes and symbols are frequently used in flowchart diagrams.
• The process symbol, also known as an "Action Symbol," represents a process, action, or function and is the most widely used symbol in flowcharting.
• A start/end symbol, also known as the "Terminator Symbol," represents the start, end, and potential outcomes of a path, typically containing "Start" or "End".
• The document symbol represents the input or output of a document, such as receiving a report, email, or order or generating a presentation, memo, or letter as output.
• The decision symbol indicates a question to be answered (usually yes/no or true/false), causing the flowchart path to split into different branches depending on the answer.
• The connector symbol connects separate elements across one page in complex charts.
• An off-page connector or link symbol connects separate elements across multiple pages, often with the page number placed within for reference.
• The input/output symbol, also known as the "Data Symbol," represents data available for input or output, including resources used or generated although the paper tape symbol also represents input/output, it is outdated.
• The comment or note symbol adds explanations or comments within the specified range, connected by a dashed line to the relevant section of the flowchart.
• Additional flowchart symbols are used for mapping out process flow diagrams for apps, user flows, and data processing.
• The database symbol represents data housed on a storage service that allows searching and filtering.
• The paper tape symbol is an outdated symbol rarely used in modern practices but can map processes or input methods on older computers and CNC machines.
• The summing junction symbol sums the input of several converging paths.
• The predefined process symbol indicates a complex process or operation that is well-known or defined elsewhere.
• The internal storage symbol maps out software designs and indicates data stored within internal memory.
• The manual input symbol represents the manual input of data, usually via a keyboard or device, such as the step in a login process where a user is prompted to enter data manually.
• The manual operation symbol indicates a step that must be done manually, not automatically.
• The merge symbol combines multiple paths into one.
• The multiple documents symbol represents multiple documents or reports.
• The preparation symbol differentiates between steps that prepare for work and steps that actually do work, helping to introduce the setup to another step within the same process.
• The stored data symbol, also known as the "Data Storage" symbol, represents where data gets stored within a process.
• The delay symbol indicates a segment of delay in a process, useful for showing the exact length of delay within the shape.
• The OR symbol indicates that the process flow continues down two or more paths.
• The display symbol is useful for showing where information will be displayed within a process flow.
• The hard disk symbol indicates data stored within a hard drive, also known as direct access storage.

Logical Schematics (Logic Gates)

• Logic gates are electronic circuits using components like diodes, transistors, and resistors.
• They perform logical operations based on inputs, giving a high (1) or low (0) logical output.
• The operation of logic gates is based on Boolean algebra or mathematics.
• Logic gates are used in telephones, laptops, tablets, and memory devices.

AND Gate

• An AND gate performs logical multiplication of binary input.
• The output is HIGH (1) if both inputs are HIGH (1); otherwise, the output is LOW (0) if any input is LOW (0).
• An AND gate can accept two or more input values at a time.
• If all inputs are logic 1, the output is logic 1.

OR Gate

• An OR gate is a widely used digital logic circuit.
• The output is HIGH (1) if any input is HIGH (1); otherwise, the output is LOW (0).
• The value of X is high (true) when one of the inputs is set to high (true).
• An OR gate can have two or more input lines.
• If all OR gate inputs are low (logic 0), the output is low (logic 0).

NOT Gate

• A NOT gate, also known as an inverter or inverting buffer, has only one input and one output.
• If the input signal is “low,” the output signal is "high," and vice versa.
• The output is the complement or inverse of the input.
• A NOT gate takes only one output.

NOR Gate

• A NOR gate is a type of universal logic gate.
• It takes two or more inputs and gives only one output.
• The output is HIGH (1) only when all inputs are LOW (0).
• A NOR gate returns the complement result of the OR gate and is a combination of OR and NOT gates.
• A NOR gate can have two or more inputs and gives an output.
• A NOR gate gives a high or logic 1 output only when all its inputs are low or logic 0.

NAND Gate

• The NAND gate is another type of universal logic gate.
• The NAND gate, or “Not AND," is a combination of AND and NOT gates connected in series.
• It takes two or more inputs and gives only one output.
• The output is HIGH (1) when either of its inputs is HIGH (1) or both inputs are LOW (0), performing the inverted operation of the AND gate.
• A NAND gate can take two or more inputs at a time and produces one output based on the combination of inputs applied.
• A NAND gate produces a low or logic 0 output only when all its inputs are high or logic 1.

XOR Gate

• An XOR gate, or Exclusive OR gate, is used to perform modulo sums in digital circuits.
• It is used extensively in arithmetic logic circuits, logic comparators, and error detection circuits.
• The XOR gate can take only two inputs at a time and give an output.
• The output is HIGH (1) only when its two inputs are dissimilar; if one is LOW (0), the other will be HIGH (1).
• It can accept only two inputs at a time. There is nothing like a three or more input XOR gate.
• The output is logic 1 or high when its inputs are dissimilar.

Applications of Logic Gates

• Logic gates are the fundamental building blocks of all digital circuits and devices like computers.
• Key digital devices using logic gates: computers, microprocessors, microcontrollers, digital and smart watches, and smartphones.

Advantages of Logic Gates

• Logic gates carry out basic logical functions like AND, OR, NOT, XOR, NAND, and NOR; all digital operations and data processing rely on these functions.
• Speed: Their extremely high speed rates make them an essential feature in today's information processing systems that aim for quickness in data analysis.
• Being elements whose behaviors are accurately defined means there is no uncertainty about how they behave when used as part of a system.
• Digital systems complexity increases by interconnecting and replicating these components without significant variations in size or complexity.
• Low Cost: Logic Gate costs are relatively low from production viewpoint thus making it popular among those who want to construct digital circuits inexpensively.
• Power consumption is minimal; hence less energy is needed for operating, making them suitable for use with gadgets without batteries or devices running low power consumption applications at all times.

Disadvantages of Logic Gates

• Complexity: The advancement and complexity of digital systems results in an increasing number of logic gates and their interconnections, which causes designs that are very difficult to handle and troubleshoot.
• Propagation Delay: Small delay in the propagating signal is introduced with every logic gate. When several such gates are chained together, these delays can add up and have adverse effects on the overall speed and performance of the circuit.
• Noise Sensitivity: Even noise, interference, and interfering fields can make logic gates sensitive to errors in the output signal. Proper shielding and conditioning of signals at times are needed to reduce these effects.
• Power Dissipation: While logic gates are essentially low power, their dissipation can grow with the complexity of the circuit. Heavy energy loss can generate thermal energy, which necessitates supplementary cooling systems.

Internet Protocol Classes & Versions

• Host Name - your device's name set by the Operating System
• MAC (Media Access Control) Address - your device's physical identifier based on its hardware
• IP (Internet Protocol) Address - your device's / website's logical identifier as seen in your network
• DNS (Domain Name System) - converts IP Addresses to words that can be read by humans

IP Classes

• There are five IP Classes used to categorize IPV4 addresses.
• These classes has their own designated uses and can be identified y the first number of the IP Address.
• Class A: 1 to 127, Many hosts per network
• Class B: 128 to 191, More hosts per network than Class A
• Class C: 192 to 223, Many networks with fewer hosts per network
• Class D: 224 to 239, Multicasting
• Class E: 240 to 255, Experimental
• Net ID - the part of an IP address given by your Network Provider
• Host ID - the part of the IP address set by your router
• Multicast Address is an IP that has the largest scope
• Reserved Address – IPs that have been reserved for experimental purposes

IPv4

• Internet Protocol version 4 is the original addressing system of the Internet, introduced in 1983.
• It uses a 32-bit address scheme, which theoretically allows for over 4 billion unique addresses (2^32).
• IPv4 addresses are typically displayed in decimal format, divided into four octets separated by dots (e.g., 192.168.1.1).
• IPv4 Address Format is a 32-bit address that comprises binary digits separated by a dot (.).

Characteristics of IPv4

• 32-bit address length allows for approximately 4.3 billion unique addresses.
• Dot-decimal notation: IP addresses are written in a format of four decimal numbers separated by dots, such as 192.168.1.1.
• Packet structure: Includes a header and payload; the header contains information essential for routing and delivery.
• Checksum fields: Uses checksums in the header for error-checking the header integrity.
• Fragmentation: Allows packets to be fragmented at routers along the route if the packet size exceeds the maximum transmission unit (MTU).
• Address Resolution Protocol (ARP): Used for mapping IP network addresses to the hardware addresses used by a data link protocol.
• Manual and DHCP configuration: Supports both manual configuration of IP addresses and dynamic configuration through DHCP (Dynamic Host Configuration Protocol).
• Limited address space: The main limitation which has led to the development of IPv6 to cater to more devices.
• Network Address Translation (NAT): Used to allow multiple devices on a private network to share a single public IP address.
• Security: Lacks inherent security features, requiring additional protocols such as IPSec for secure communications.

Drawbacks of IPv4

• Limited Address Space: IPv4 has a limited number of addresses, which is not enough for the growing number of devices connecting to the internet.
• Complex Configuration : IPv4 often requires manual configuration or DHCP to assign addresses, which can be time-consuming and prone to errors.
• Less Efficient Routing : The IPv4 header is more complex, which can slow down data processing and routing.
• Security Issues: IPv4 does not have built-in security features, making it more vulnerable to attacks unless extra security measures are added.
• Limited Support for Quality of Service (QoS) : IPv4 has limited capabilities for prioritizing certain types of data, which can affect the performance of real-time applications like video streaming and VoIP.
• Fragmentation: IPv4 allows routers to fragment packets, which can lead to inefficiencies and increased chances of data being lost or corrupted.
• Broadcasting Overhead : IPv4 uses broadcasting to communicate with multiple devices on a network, which can create unnecessary network traffic and reduce performance.

IPv6

• The most common version of the Internet Protocol currently is IPv6.
• IPv6 was designed by the Internet Engineering Task Force (IETF) in December 1998 with the purpose of superseding IPv4 due to the global exponentially growing internet of users.
• IPv6 stands for Internet Protocol version 6. IPv6 is the new version of Internet Protocol, which is way better than IPv4 in terms of complexity and efficiency.
• IPv6 is written as a group of 8 hexadecimal numbers separated by colon (:). It can be written as 128 bits of 0s and 1s.
• IPv6 Address Format is a 128-bit IP Address, which is written in a group of 8 hexadecimal numbers separated by colon (:).

Switching from IPv4 to IPv6

• Dual Stacking : Devices can use both IPv4 and IPv6 at the same time allowing communications using either version.
• Tunneling: Enables IPv6 users to send data through an IPv4 network to reach other IPv6 users, creating a "tunnel" for IPv6 traffic through the older IPv4 system.
• Network Address Translation (NAT) : Helps devices using different versions of IP addresses (IPv4 and IPv6) to communicate by translating the addresses so they understand each other.

Characteristics of IPv6

• IPv6 uses 128-bit addresses, offering a much larger address space than IPv4's 32-bit system.
• IPv6 addresses use a combination of numbers and letters separated by colons, allowing for more unique addresses.
• The IPv6 header has fewer fields, making it more efficient for routers to process.
• IPv6 supports Unicast, Multicast, and Anycast, but no Broadcast, reducing network traffic.
• IPv6 allows flexible subnetting (VLSM) to divide networks based on specific needs.
• IPv6 uses Neighbor Discovery for MAC address resolution instead of ARP.
• IPv6 uses advanced routing protocols like OSPFv3 and RIPng for better address handling.
• IPv6 devices can self-assign IP addresses using SLAAC, or use DHCPv6 for more control.
• IPv6 handles fragmentation at the sender side, not by routers, improving speed.

Difference between IPv4 and IPv6

• IPv4 has a 32-bit address length; IPv6 has a 128-bit address length.
• IPv4 supports manual and DHCP address configuration; IPv6 supports auto and renumbering address configuration.
• In IPv4 end-to-end, connection integrity is unachievable; in IPv6 end-to-end, connection integrity is achievable.
• IPv4 can generate 4.29x10^9 address space; IPv6 can produce 3.4x10^38 address space.
• The Security feature in IPv4 is dependent on the application; IPSEC is an inbuilt security feature in IPv6.
• The address representation of IPv4 is in decimal; the address representation of IPv6 is in hexadecimal.
• Fragmentation is performed by the sender and forwarding routers in IPv4; fragmentation is performed only by the sender in IPv6.
• IPv4 packet flow identification is not available; IPv6 packet flow identification is available and uses the flow label field in the header.
• IPv4 checksum field is available; IPv6 checksum field is not available.
• IPv4 has a broadcast Message Transmission Scheme; IPv6 has multicast and anycast message transmission schemes available.
• IPv4 Encryption and Authentication facility is not provided; IPv6 Encryption and Authentication are provided.
• IPv4 has a header of 20-60 bytes; IPv6 has a fixed header of 40 bytes.
• IPv4 can be converted to IPv6; not all IPv6 can be converted to IPv4.
• IPv4 consists of 4 fields separated by dots; IPv6 consists of 8 fields, separated by colons.
• IPv4's IP addresses are divided into five different classes (A, B, C, D, E); IPv6 does not have any classes.
• IPv4 supports VLSM; IPv6 does not support VLSM.
• Example of IPv4: 66.94.29.13; Example of IPv6: 2001:0000:3238:DFE1:0063:0000:0000:FEFB

Benefits of IPv6 over IPv4

• Larger Address Space: IPv6 has a greater address space than IPv4. IPv6 has 128 bit IP Address rather and IPv4 has a 32-bit Address.
• Improved Security: IPv6 has improved security with built-in features like Data Authentication and Data Encryption, for a more secure Internet connection.
• Simplified Header Format: Compared to IPv4, IPv6 has a simpler and more effective header structure, making it more cost-effective and increasing internet speed.
• Prioritize: IPv6 contains stronger and more reliable support for QoS features, helping to increase traffic over websites and improve audio and video quality.
• Improved Support for Mobile Devices: IPv6 has increased and better support for Mobile Devices and helps make quick connections and is a safer way than IPv4.

Why IPv4 is Still in Use

• Infrastructure Compatibility: Many systems and devices are built for IPv4 and require significant updates to support IPv6, including routers, switches, and computers.
• Cost of Transition: Switching to IPv6 can be expensive and complex, involving hardware updates, software upgrades, and training for personnel.
• Lack of Immediate Need: Techniques like NAT (Network Address Translation) help extend the life of IPv4 by allowing multiple devices to share a single public IP address, reducing the urgency to switch to IPv6.
• Coexistence Strategies: Technologies that allow IPv4 and IPv6 to run simultaneously make it easier for organizations to adopt IPv6 gradually while maintaining their existing IPv4 systems.
• Slow Global Adoption: The adoption of IPv6 varies significantly around the world, which necessitates the continued support of IPv4 for global connectivity.
• Lack of Visible Benefits: Many users and organizations don't see immediate improvements with IPv6 if they don't face an IP address shortage, reducing the incentive to upgrade.

Introduction of Firewalls in Computer Networks

• A firewall is a network security device (hardware or software-based) that monitors all incoming and outgoing traffic, and, based on defined security rules, it accepts, rejects, or drops traffic to protect from unwanted visitors and potential threats.
• Accept: allow the traffic
• Reject: block the traffic but reply with an “unreachable error"
• Drop: block the traffic with no reply
• A firewall filters incoming and outgoing network traffic with security policies and separates a private internal network from the open Internet.

Need for Firewalls

• Before Firewalls, network security was performed by Access Control Lists (ACLs) that determine whether network access should be granted or denied to specific IP address.
• ACLs cannot determine the nature of the packet it is blocking without the capacity to keep threats out of the network and are not sufficient for securing internal networks from unauthorized traffic.

History of Firewalls

• Late 1980s: Jeff Mogul, Brian Reid, and Paul Vixie at Digital Equipment Corp (DEC) developed packet-filtering technology by checking external connections before they reached internal networks.
• Late 1980s – Early 1990s: AT&T Bell Labs researchers developed the circuit-level gateway, a firewall that vetted ongoing connections without reauthorizing each data packet.
• 1991-1992: Marcus Ranum introduced security proxies at DEC, leading to the creation of the Secure External Access Link (SEAL), the first commercially available application-layer firewall.
• 1993-1994: At Check Point, Gil Shwed pioneered stateful inspection technology, and Nir Zuk developed a graphical interface for Firewall-1.

Working of Firewalls

• A firewall matches network traffic against a defined rule set and applies the associated action. For example, rules are set so an employee cannot access data and rules are set so the system admin can access data.
• Rules can be defined on the firewall based on the necessity and security policies of the organization.
• Network traffic can be either outgoing or incoming and the firewall maintains a distinct set of rules for both cases.
• Most traffic on the firewall uses Transport Layer protocols (TCP, UDP, or ICMP), which have a source and destination address as well as port numbers or type codes to identify the purpose of the packet.
• Default policy: Default policy only consists of action (accept, reject or drop) and should be set to drop (or reject) as a good practice.

Types of Firewalls

• Firewalls can be categorized based on their generation.
• Packet Filtering Firewall: Controls network access by monitoring packets and allowing them to pass or stop based on source and destination IP address, protocols, and ports analyzing traffic at the transport protocol layer (but mainly uses first 3 layers) and maintaining a filtering table.
• Stateful Inspection Firewall: Are able to determine the connection state of packet, unlike Packet filtering firewall, which makes it more efficient and keeps track of the state of networks connection travelling across it, such as TCP streams.
• Application Layer Firewall: Can inspect and filter the packets on any OSI layer, up to the application layer, has the ability to block specific content, also recognize when certain application and protocols (like HTTP, FTP) are being misused, prevents direct connection between either side of the firewall, each packet has to pass through the proxy..
• Next Generation Firewalls (NGFW): Consists of Deep Packet Inspection, Application Inspection, SSL/SSH inspection and many functionalities to protect the network from these modern threats.
• Circuit Level Gateway Firewall: Works as the Sessions layer of the OSI Model', allows for the simultaneous setup of two Transmission Control Protocol (TCP) connections, can effortlessly allow data packets to flow without using quite a lot of computing power' and is ineffective because they do not inspect data packets
• Software Firewall: Any firewall that is set up locally or on a cloud server, are time-consuming and limits the number of networks that can be linked to a single device.
• Hardware Firewall: Also go by the name “firewalls based on physical appliances,” it guarantees that the malicious data is halted before it reaches the network endpoint that is in danger.
• Cloud Firewall: These are software-based, cloud-deployed network devices that protect a private network from unwanted access and filters data at the cloud level.

Importance of Firewalls

• Without protection, networks are vulnerable to harmful traffic trying to access your systems.
• Connecting personal computers to other IT systems or the internet opens up many benefits but also exposes your network and devices to risks.
• Using a firewall is essential for proactive protection against these risks and helps users shield their networks from the worst dangers.

What Firewalls Protect Against

• Infiltration by Malicious Actors: Firewalls can block suspicious connections, preventing eavesdropping and advanced persistent threats (APTs).
• Parental Controls: Parents can use firewalls to block their children from accessing explicit web content.
• Workplace Web Browsing Restrictions: Employers can restrict employees from using the company network to access certain services and websites, like social media.
• Nationally Controlled Intranet: Governments can block access to certain web content and services that conflict with national policies or values.
• Firewalls offer customizable protection for various scenarios, enhancing overall network security.

Advantages of Using Firewalls

• Protection From Unauthorized Access: Firewalls can restrict incoming traffic from particular IP addresses or networks, preventing hackers or other malicious actors from accessing a network or system and providing protection from unwanted access.
• Prevention of Malware and Other Threats: Assists in the defense against malware.
• Control of Network Access: Limiting access to specified individuals or groups for particular servers or applications, firewalls can be used to restrict access to particular network resources or services.
• Monitoring of Network Activity: Record and keep track of all network activity.
• Regulation Compliance: Many industries are bound by rules that demand the usage of firewalls or other security measures.
• Network Segmentation: Reduces the attack surface and raises the level of security.

Disadvantages of Using Firewalls

• Complexity: Complex for bigger networks with many users and devices.
• Limited Visibility: Because they can only observe and manage traffic at the network level firewalls cannot observe security risks that operate at other levels.
• False Sense of Security: Some businesses may place an excessive amount of reliance on their firewall and disregard other crucial security measures.
• Limited Adaptability: Firewalls might not be able to respond to fresh security threats because often they are rule-based.
• Performance Impact: Heavily impacted with a lot of traffic.
• Limited Scalability: They can only secure one network and can be expensive.
• Limited VPN support: Complex VPN features might not be allowed.
• Cost: Purchasing many devices or add-on features can be expensive.