How the Internet Works: IP Addresses, DNS, and Vint Cerf's Protocol

Firewalls monitor and control network traffic based on security rules, acting as barriers between trusted internal networks and untrusted external networks. HTTPS (HyperText Transfer Protocol Secure) encrypts data transmitted between browsers and websites, ensuring confidential online transactions. Cybercrime encompasses illegal activities like unauthorized system access, data theft, and password cracking. Types include tampering with systems, publishing confidential information, and distributing harmful content. Understanding these concepts helps users protect their digital assets and online activities.

Network security relies on encryption (converting plaintext to ciphertext using keys), authentication (verifying identity through digital certificates issued by Certificate Authorities), and digital signatures (using hash functions and private key encryption to ensure data integrity and non-repudiation). HTTPS combines HTTP with SSL/TLS protocols, which use a three-way handshake to negotiate encryption algorithms, exchange keys, and verify server certificates, enabling secure web communication.

This section covers HTTP vs HTTPS protocols: HTTP is not secure, while HTTPS uses encryption to scramble data before sending, essential for banking and shopping websites. HTTPS uses SSL certificates to ensure data is encrypted and websites are genuine. Firewalls are security tools that protect computers and networks from unauthorized access and harmful data. They act like security guards monitoring all incoming and outgoing data. Types include network firewalls (protect entire networks between multiple networks) and host-based firewalls (protect single computers). Firewalls follow rules to allow safe data while blocking threats like viruses and hackers.

This section explains network security concepts including firewalls that prevent unauthorized access, HTTP/HTTPS protocols for web browsing, SSL encryption for secure communications, and Windows file systems (NTFS and FAT). It also covers the purpose of firewalls in blocking malicious programs and viruses.

A firewall is a security system that prevents unauthorized access to a computer network, acting like a barrier that controls what data can enter and leave the network. Firewalls can be hardware devices, software programs, or a combination of both. They block unauthorized access while allowing legitimate traffic, protecting sensitive data and systems from external threats. Website cookies are small text files that websites store on users' computers, storing information about user preferences, login details, and browsing history. First-party cookies are created by the website the user is visiting for legitimate purposes, while third-party cookies are created by other websites and can track user activity across different websites. Secure websites are identified by 'https://' in their URL and display a lock icon, indicating encrypted data transmission that protects sensitive information from interception. Encryption is the process of converting readable data (plaintext) into coded data (ciphertext) to protect it from unauthorized access. Decryption is the reverse process of converting coded data back to readable form. Only authorized parties with the correct decryption key can read the original data. In secure communication, data is encrypted before transmission and decrypted by the recipient, ensuring that even if data is intercepted during transmission, unauthorized parties cannot read it.

BGP (Border Gateway Protocol) is the standard routing protocol used by Internet Service Providers (ISPs) to exchange routing information and determine the best paths for data transmission across interconnected networks, enabling efficient and reliable internet communication between different network domains.

BGP (Border Gateway Protocol) is used for routing between different networks on the Internet, particularly between different ISPs (Internet Service Providers). Unlike RIP and OSPF which are used within organizations, BGP handles routing between autonomous systems. BGP uses path vectors and policy-based routing, allowing ISPs to control how traffic flows between their networks. This protocol is essential for the global Internet routing infrastructure.

This section covers BGP (Border Gateway Protocol) and VRF (Virtual Routing and Forwarding) technologies essential for ISP operations. BGP, defined in RFC 1771, serves as the primary protocol for inter-domain routing, sustaining VRF instances and enabling communication between different network domains. VRF technology allows creating multiple virtual routers within a single physical device, enabling network administrators to isolate customer traffic and provide each customer with independent routing tables. This isolation prevents customers from seeing each other's routing information and reduces the routing table size each customer must process, improving both security and performance.

Routing protocols are categorized into Interior Gateway Protocols (IGP) and Exterior Gateway Protocols (EGP). IGP protocols (RIP, EIGRP, OSPF, IS-IS) are used for internal routing within a single Autonomous System (AS), even across geographically distant branches. BGP (Border Gateway Protocol) is the only EGP in the world, essential for internet routing. Each AS is assigned a unique AS number. Companies connect to ISPs through three types of connectivity: Single Home (one connection to one ISP), Dual Home (multiple connections to the same ISP), and Multi-Home (connections to multiple different ISPs). BGP provides two major benefits: traffic control and public IP advertisement, enabling companies like Facebook and Google to make their services accessible globally.

BGP (Border Gateway Protocol) is the exterior gateway protocol used between autonomous systems. Unlike interior protocols (RIP, OSPF) used within ASes, BGP enables ISPs to exchange network reachability information. ISP1 tells ISP2 about networks A-T, ISP2 tells ISP1 about networks U-Z. When a host on ISP3's network needs to reach subnet A, the border router knows (via BGP) that subnet A is on ISP2's network, so it routes through ISP2 to ISP1. This enables global internet routing.

IP addresses are unique identifiers for devices on the internet, with IPv4 using 32-bit addresses (4 octets separated by dots) and IPv6 using 128-bit addresses (8 hextets separated by colons); IPv6 employs zero compression for shorthand notation; subnetting divides networks by partitioning the host ID into subnet ID and host ID to reduce traffic complexity; dynamic IP addresses change upon reconnection while static IPs remain constant; public IPs are globally routable and assigned by ISPs, whereas private IPs (ranging from 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16) are used internally and require NAT (Network Address Translation) to access the internet, allowing multiple devices to share a single public IP address.

Network Address Translation (NAT) enables multiple devices in a local network to share a single public IP address by translating private IP addresses (like 10.0.0.0/8, 172.16.0.0/12, or 192.168.0.0/16) to a public IP address at the router, while IPv6 addresses the IPv4 address exhaustion problem through a 128-bit address space and simplified header design; the transition between IPv4 and IPv6 networks is achieved through tunneling, where IPv6 datagrams are encapsulated within IPv4 datagrams to traverse IPv4-only networks.

IPv4 uses 32-bit addresses divided into four decimal octets, while IPv6 uses 128-bit addresses in hexadecimal format with eight groups separated by colons; subnetting involves dedicating bits from the host portion to the network portion to create smaller networks, while supernetting combines multiple consecutive IP addresses to accommodate large numbers of hosts, both techniques being essential for efficient network management in modern networking environments.

NAT64 is a translation technique that enables communication between IPv6-only and IPv4-only networks by using a NAT64 prefix (such as 64:ff9b::/96), where a DNS64 server synthesizes IPv6 addresses from IPv4 addresses and a NAT64 router performs the actual header translation between IPv6 and IPv4 packets, allowing hosts on IPv6-only networks to access IPv4-only services.

IPv4 provides approximately 4.3 billion unique addresses (2^32), but this is insufficient for modern needs where each person may have multiple devices. The classful addressing system caused significant waste—for example, a company needing only 300 devices would have to use a Class B network providing 65,534 addresses. Three solutions emerged: IPv6 (providing vastly more addresses using hexadecimal notation), NAT (Network Address Translation) allowing multiple private devices to share one public IP, and private IP address ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) that cannot be routed on the public internet. While IPv6 adoption is ongoing, most networks still rely on IPv4 with NAT for internet connectivity. NAT works by having a router translate private IP addresses to a single public IP when communicating with the internet, allowing multiple devices to share one public IP address while maintaining internal network communication.