Common Network Ports

• Port 20 and 21 are used for FTP (File Transfer Protocol); port 20 is for data transfer, and port 21 is for control/commands.
• Port 22 is for SSH (Secure Shell), which provides encrypted remote login and command execution.
• Port 23 is for Telnet, an unencrypted remote login protocol (insecure, legacy).
• Port 25 is for SMTP (Simple Mail Transfer Protocol), used to send email.
• Port 53 is for DNS (Domain Name System), which resolves hostnames to IP addresses, using UDP/TCP.
• Ports 67 and 68 are used for DHCP, which automatically assigns IP addresses, using UDP.
• Port 69 is for TFTP, a Trivial File Transfer Protocol with no authentication, using UDP.
• Port 80 is for HTTP, which is unencrypted web traffic.
• Port 110 is for POP3, which retrieves email from a server.
• Port 123 is for NTP, the Network Time Protocol, using UDP.
• Port 143 is for IMAP, which retrieves and manages email on the server.
• Ports 161 and 162 are used for SNMP, which manages and monitors network devices, using UDP.
• Port 389 is for LDAP, a Lightweight Directory Access Protocol (plain text).
• Port 443 is for HTTPS, which provides secure, encrypted web traffic.
• Port 445 is for SMB, used for Windows file and printer sharing.
• Port 636 is for LDAPS, a secure version of LDAP.
• Port 993 is for IMAPS, a secure version of IMAP.
• Port 995 is for POP3S, a secure version of POP3.
• Port 1723 is for PPTP, a VPN tunneling protocol (legacy and insecure).
• Ports 1812 and 1813 are for RADIUS, a Remote Authentication Dial-In User Service; 1812 for Authentication, 1813 for Accounting.
• Port 3389 is for RDP, the Remote Desktop Protocol, used for Windows remote access.

RAID Levels

• RAID 0 (Striping): Requires a minimum of 2 drives, offers no redundancy, and provides high performance, suitable for situations where fault tolerance is not critical (e.g., gaming, temp files).
• RAID 1 (Mirroring): Requires 2 drives, provides redundancy, and offers medium performance, ideal for critical systems with small data sets needing maximum uptime.
• RAID 5 (Striping with Parity): Requires 3 drives, provides redundancy, and offers good performance, balancing speed and fault tolerance, suitable for web servers and databases.
• RAID 6 (Striping with Dual Parity): Requires 4 drives and can withstand the loss of 2 drives, offering lower performance than RAID 5 but providing high availability for systems.
• RAID 10 (Mirrored Sets): Requires 4 drives, provides redundancy, and offers high performance, suited for applications needing both performance and redundancy, such as databases and virtual servers.

TCP/IP and OSI Model

• Application Layer: In TCP/IP, maps to OSI Layers 7 (Application), 6 (Presentation), and 5 (Session) and key protocols include HTTP, FTP, SMTP, DNS, TLS, SSH.
• Transport Layer: Maps to OSI Layer 4 (Transport) and key protocols are TCP and UDP.
• Internet Layer: Maps to OSI Layer 3 (Network) and key protocols are IP, ICMP, ARP, and IPsec.
• Network Access Layer: Maps to OSI Layers 2 (Data Link) & 1 (Physical) and key protocols are Ethernet, MAC addresses, Wi-Fi, and Frame Relay.

OSI Model Layers

• Layer 7 (Application): Provides a user interface and network services to applications. Examples include HTTP, FTP, SMTP, DNS, and Telnet.
• Layer 6 (Presentation): Handles data translation, encryption/decryption, and compression, with examples like SSL/TLS, JPEG, and ASCII.
• Layer 5 (Session): Establishes, manages, and ends sessions, with examples like NetBIOS and RPC.
• Layer 4 (Transport): Provides end-to-end communication and flow control, using protocols like TCP and UDP.
• Layer 3 (Network): Handles routing and logical addressing, using protocols like IP, ICMP, and IPsec.
• Layer 2 (Data Link): Manages MAC addressing and error detection, using technologies like Ethernet, ARP, PPP, and Switches.
• Layer 1 (Physical): Transmits raw bits via cables and signals, utilizing Cables, NICs, Hubs, and RF.

Public Key Infrastructure (PKI)

• PKI is a framework for managing digital certificates and public-key encryption.
• PKI uses asymmetric encryption, which relies on a public and private key pair.
• A digital certificate is an electronic document that proves ownership of a public key, issued and signed by a Certificate Authority (CA).
• A Certificate Authority (CA) issues, validates, and revokes digital certificates.
• A Registration Authority (RA) verifies user identity before certificates are issued by the CA.
• A CSR (Certificate Signing Request) is a request generated by an entity to apply for a digital certificate from a CA.
• The public key in PKI encrypts data or verifies digital signatures.
• The private key in PKI decrypts data or creates digital signatures.
• A CRL (Certificate Revocation List) is a list published by the CA containing revoked certificates that should no longer be trusted.
• OCSP (Online Certificate Status Protocol) is a real-time protocol for checking the revocation status of a digital certificate.
• Key escrow involves a trusted third party securely storing private encryption keys for recovery or legal access.
• A Root CA is the top-level authority and is self-signed.
• An Intermediate CA is subordinate and signs end-entity certificates.
• Digital signatures are used for integrity, authentication, and non-repudiation.
• A Wildcard Certificate applies to all subdomains of a domain (e.g., *.example.com).
• A SAN (Subject Alternative Name) Certificate is used for multiple domains or services on one certificate.
• The hierarchical trust model is based on a central authority, where the Root CA signs Intermediate CAs.
• The web of trust model is decentralized and peer-based, used in PGP, and relies on individuals signing each other's keys.
• PKI is an asymmetric system that uses a public and private key pair.
• Digital certificates are typically encoded in X.509 format.

AES Versions

• AES-128: Uses a 128-bit key size and a 128-bit block size.
• AES-192: Uses a 192-bit key size and a 128-bit block size.
• AES-256: Uses a 256-bit key size and a 128-bit block size.