1. Network Operating Systems & Maintenance Models

• NOS Definition: A Network Operating System (NOS) supports workstations, personal computers, and terminals across a Local Area Network (LAN). Examples include Novell NetWare, Banyan VINES, Microsoft LAN Manager, Windows Server, RedHat Linux, and Ubuntu Server.

• Network Maintenance: Encompasses tasks required to keep a network operational, including troubleshooting, hardware/software installation, performance monitoring, growth planning, documentation, legal compliance, and security enforcement.

• Maintenance Models: Tasks are divided into structured tasks (a proactive, planned approach that resolves issues before they occur to reduce downtime and costs) and interrupt-driven tasks (a reactive "fireman" approach to unexpected failures).

• Five Elements of Network Management:

  1. Fault Management: Configures devices (routers, switches, firewalls) to capture logs and issue automated alerts (e.g., interface down or CPU > 80%).

  2. Configuration Management: Tracks and logs all changes made to network devices using change management procedures.

  3. Accounting Management: Tracks and bills for resource usage, such as wireless data or VoIP calls.

  4. Performance Management: Monitors LAN/WAN link health and sets Quality of Service (QoS) rules.

  5. Security Management: Implements security policies using firewalls, VPNs, Intrusion Prevention Systems (IPS), and AAA authentication servers.

2. Security Roles & OS Comparison (Windows NT vs. Linux)

• Network Security Specialist: Responsible for assessing IT risks, implementing safety/recovery plans, configuring security software, inspecting vulnerability points, monitoring network traffic, and responding to security breaches.

• Windows NT: A 32-bit NOS released in 1993 (available in Workstation and Server editions) that introduced the NTFS file system, supporting automatic disk error recovery, permission controls, and file encryption. It supports preemptive multitasking and remote logons, though unpatched versions are vulnerable to malware and instability.

• Linux vs. Windows: Linux is open-source, free, highly customizable, requires no licensing, operates reliably without frequent reboots, provides strong security, and uses case-sensitive file names. Windows is commercial, closed-source, requires paid licensing, uses case-insensitive file names, and is more vulnerable to malware.

3. Firewall Technologies & IPTables

• Firewall Fundamentals: An intermediary security system filtering traffic based on predetermined rules, available as software (server applications) or hardware (dedicated appliances).

• Five Types of Firewalls:

  1. Packet Filtering Firewall: Inspects inline traffic at routers/switches using IP headers, port numbers, and address criteria.

  2. Circuit-Level Gateway: Monitors TCP handshakes and session initiation messages.

  3. Stateful Inspection Firewall: Tracks packet state and active TCP connections.

  4. Application-Level Gateway (Proxy): Filters traffic based on application characteristics (such as HTTP request strings).

  5. Next-Generation Firewall (NGFW): Combines packet inspection, deep packet inspection, intrusion prevention, and malware filtering.

• IPTables: The default Linux kernel utility used to set up, maintain, and inspect IPv4 and IPv6 packet-filtering rules.

4. Storage Management & File Systems

• Disk Partitioning (Slicing): Divides a physical hard drive into separate logical regions so the operating system can manage data independently in each region, recorded in a partition table.

• Logical Volume Manager (LVM): Flexible storage management managing three tiers: Physical Volumes (PV)(raw disks), Volume Groups (VG) (pools combining physical volumes), and Logical Volumes (LV) (flexible partitions holding file systems that can span across multiple non-contiguous physical disks).

• Linux File Hierarchy & Mount Points: Linux organizes files in a tree-based hierarchy rooted at / where everything is treated as a file. External storage devices must be attached to a specific directory using the mountcommand (e.g., mount /dev/cdrom /mnt/cdrom) before files can be accessed, and detached using umount.

• Swap Space: Hard drive space allocated as virtual memory when physical RAM is full. Idle memory pages are moved from RAM to swap (page out), and required pages are restored back to RAM (page in).

5. Administration & User Management

• File Permissions: Access controls are categorized into three groups (owner u, group g, all users o/a) and three types (read r, write w, execute x), modified using the chmod command.

• Shell Scripting: Saves command sequences into executable .sh files to automate routine tasks, system monitoring, and backups.

• User & Group Administration: Managed using terminal commands (sudoadduser, sudogroupadd, sudousermod, sudodeluser) or Ubuntu graphical settings (User Accounts).