Networking Questions for SSC CGL

Types of Networks

Networks are classified by geographic size and coverage. The three main types are LAN, MAN, and WAN. Think of them as Room, City, and World — each bigger than the previous. A PAN (Personal Area Network) is even smaller than LAN and covers a single person's devices, like Bluetooth connecting your phone and earphones.

• LAN (Local Area Network): Small area like a room, building, or campus. High speed, privately owned.
• MAN (Metropolitan Area Network): City-wide network, e.g., cable TV networks in a city.
• WAN (Wide Area Network): Spans countries or continents. The internet is the largest WAN.
• PAN (Personal Area Network): A few metres range, e.g., Bluetooth, USB.
• VPN (Virtual Private Network): A secure private tunnel over the public internet.

Network Devices

Network devices connect computers and manage data flow. Each device works at a specific layer of the OSI model, which is a common exam angle. Remember the mnemonic RHBS: Repeater, Hub, Bridge, Switch — each smarter than the previous.

• Repeater: Amplifies/regenerates signal. Works at Physical layer (Layer 1).
• Hub: Broadcasts data to all connected devices. Dumb device. Layer 1.
• Switch: Sends data only to the target device using MAC addresses. Layer 2 (Data Link).
• Router: Connects different networks, uses IP addresses. Layer 3 (Network).
• Bridge: Connects two LAN segments, filters traffic by MAC address. Layer 2.
• Gateway: Connects networks with different protocols. Works at all layers — acts as a translator.
• Modem: Converts digital signals to analog and back (MOdulator + DEModulator).

OSI Model

The OSI (Open Systems Interconnection) model has 7 layers that describe how data travels from one device to another. SSC CGL frequently asks which layer a device or protocol belongs to. Remember the layers from top to bottom using the mnemonic: All People Seem To Need Data Processing.

• Layer 7 - Application: HTTP, FTP, SMTP, DNS (user-facing services).
• Layer 6 - Presentation: Data encryption, compression, translation.
• Layer 5 - Session: Manages sessions/connections between applications.
• Layer 4 - Transport: TCP and UDP, end-to-end delivery, error checking.
• Layer 3 - Network: IP addressing and routing. Router works here.
• Layer 2 - Data Link: MAC addresses, Switch and Bridge work here.
• Layer 1 - Physical: Actual cables, bits, Repeater and Hub work here.

Protocols

A protocol is a set of rules for communication. SSC CGL loves asking what each protocol does or which port number it uses. Focus on the most common ones and their purpose rather than technical depth.

• HTTP (Port 80): Transfers web pages. HTTPS (Port 443) is its secure version.
• FTP (Port 21): File Transfer Protocol, used to upload/download files.
• SMTP (Port 25): Sends emails. POP3 (Port 110) and IMAP (Port 143) receive emails.
• DNS: Converts domain names (google.com) to IP addresses. Like a phone book for the internet.
• DHCP: Automatically assigns IP addresses to devices on a network.
• TCP: Connection-oriented, reliable delivery. UDP: Connectionless, faster but unreliable.
• IP: Internet Protocol, handles addressing and routing of packets.

IP Addressing and Subnetting Basics

Every device on a network has an IP address. IPv4 uses 32 bits (written as four octets: e.g., 192.168.1.1). IPv6 uses 128 bits to solve address exhaustion. Classes of IP addresses define the range of networks vs hosts. SSC CGL asks about classes, private IP ranges, and differences between IPv4 and IPv6.

• Class A: 1.0.0.0 to 126.255.255.255 — large networks, first octet is network part.
• Class B: 128.0.0.0 to 191.255.255.255 — medium networks.
• Class C: 192.0.0.0 to 223.255.255.255 — small networks (most common for home/office).
• 127.0.0.1 is the loopback address (localhost) — refers to your own computer.
• Private IP ranges (not routable on internet): 10.x.x.x, 172.16-31.x.x, 192.168.x.x.
• IPv4: 32-bit, about 4.3 billion addresses. IPv6: 128-bit, virtually unlimited addresses.

Internet Terms and Concepts

SSC CGL also tests general internet and networking vocabulary. These are pure recall questions — no calculations involved. Pay attention to exact definitions as options are often tricky near-synonyms.

• URL (Uniform Resource Locator): Web address of a resource, e.g., https://www.ssc.nic.in
• ISP (Internet Service Provider): Company that provides internet access, e.g., BSNL, Jio.
• Bandwidth: Maximum data transfer rate of a network, measured in bps/Mbps/Gbps.
• Latency: Delay in data transmission. Low latency is better.
• Firewall: Security system that monitors and controls incoming/outgoing network traffic.
• Proxy Server: Acts as an intermediary between user and internet, provides anonymity and caching.
• Wi-Fi: Wireless LAN technology based on IEEE 802.11 standard.

• Confusing Hub and Switch: Hub broadcasts to ALL devices (dumb), Switch sends only to the TARGET device (smart). Very common trap question.
• Mixing up SMTP, POP3, IMAP: SMTP is for SENDING emails only. POP3 and IMAP are for RECEIVING. Remember S for Send.
• Thinking Router and Gateway are the same: Router connects networks using the same protocol. Gateway connects networks using DIFFERENT protocols.
• Confusing IPv4 and IPv6 bit lengths: IPv4 is 32-bit, IPv6 is 128-bit. Aspirants often reverse these under pressure.
• Forgetting that 127.0.0.1 is localhost/loopback — it does not represent an external device. This appears as a tricky option in MCQs.

• OSI Layers top to bottom: All People Seem To Need Data Processing (Application, Presentation, Session, Transport, Network, Data Link, Physical).
• Network size order: PAN, LAN, MAN, WAN — Please Let Me Work (Personal, Local, Metro, Wide).
• MODEM = MOdulator + DEModulator — it modulates (digital to analog) and demodulates (analog to digital).
• SMTP Sends, POP3 Pulls — S for Send, P for Pull/Receive. Easy to remember at exam time.

• SSC CGL typically asks 2-3 networking questions in Tier 1 Computer Awareness. They are fully factual, so this section is a high-reward, low-effort area if memorised well.
• Device-layer mapping is a favourite: expect options like which layer does a Router/Switch/Hub operate at. Always link: Router=Layer 3, Switch=Layer 2, Hub=Layer 1.
• Protocol-to-function matching is very common: a question gives you FTP or SMTP and asks its purpose or port. Learn top 8 protocols with port numbers.
• IPv4 vs IPv6 differences (bit size, address notation, capacity) appear as direct one-liner questions. Also watch for loopback address 127.0.0.1.
• Recent papers have included questions on VPN, Firewall, and Proxy Server — these were rare earlier but now appear regularly. Do not skip them.