Computer Networks Interview Questions — Easy

A computer network is a collection of interconnected computing devices (nodes) that share resources, exchange data, and communicate via wired or wireless media.

• Nodes: PCs, servers, routers, switches, IoT devices.
• Links: Fiber optics, coaxial cables, copper wires, radio waves.
• Purpose: Resource sharing (files, printers), communication (emails, video), and application hosting.

The Open Systems Interconnection (OSI) model is a conceptual framework standardizing network communication into seven logical layers:

1. Physical (Layer 1): Transmits raw unstructured bit streams over physical media (electrical, optical, radio).
2. Data Link (Layer 2): Provides reliable node-to-node frame delivery, error detection, and MAC addressing.
3. Network (Layer 3): Handles packet routing, logical addressing (IP), and path determination.
4. Transport (Layer 4): Ensures end-to-end reliability, flow control, congestion control, and segmenting (TCP/UDP).
5. Session (Layer 5): Establishes, manages, and terminates communication sessions between applications.
6. Presentation (Layer 6): Translates, encrypts, and compresses data (syntax layer, e.g., SSL/TLS, ASCII, JPEG).
7. Application (Layer 7): Provides direct user interfaces and protocols for software applications (HTTP, DNS, SMTP).

The TCP/IP model is a practical suite of communication protocols used on the modern Internet. It consolidates the OSI model into 4 or 5 layers:

1. Network Access (or Link) Layer: Combines OSI's Physical and Data Link layers. Manages physical transmission and hardware addressing.
2. Internet Layer: Equivalent to OSI's Network layer. Routes packets across networks using logical IP addresses.
3. Transport (Host-to-Host) Layer: Matches OSI's Transport layer. Manages end-to-end communication, reliability, and flow control.
4. Application Layer: Merges OSI's Session, Presentation, and Application layers. Provides high-level APIs and user services.

• TCP (Transmission Control Protocol): Connection-oriented, guarantees ordered/reliable packet delivery, supports flow and congestion control, overhead is higher (20-byte header). Used for HTTP, FTP, SMTP.
• UDP (User Datagram Protocol): Connectionless, best-effort/unreliable delivery, no flow/congestion control, minimal overhead (8-byte header). Used for DNS, VoIP, video streaming, gaming.

Domain Name System (DNS) translates human-readable domain names (e.g., example.com) to machine-readable IP addresses (e.g., 192.0.2.1).

• Resolving Name Server: Receives queries from client machines.
• Root Name Server: Directs the resolver to the Top-Level Domain (TLD) server (e.g., .com).
• TLD Name Server: Directs the resolver to the Authoritative Name Server.
• Authoritative Name Server: Contains the actual IP mapping and returns it to the resolver.