Network Basics — Q&A

Networking is the practice of connecting computers, servers, and other devices to share data and resources such as files, internet, printers, etc.

LAN (Local Area Network): A small network within a home, office, or building.

WAN (Wide Area Network): A large network spread over a wide geographical area like the Internet.

MAN (Metropolitan Area Network): A network that spans a city or large campus.

• Router: Connects different networks and routes data between them.
• Switch: Connects devices in a LAN and forwards data based on MAC addresses.
• Modem: Converts digital data to analog (and vice versa) for internet connectivity.
• Access Point: Enables wireless devices to connect to a wired network.
• Hub (outdated): Broadcasts data to all connected devices regardless of destination.

• Cat5: Up to 100 Mbps, max length 100m (mostly outdated).
• Cat5e: Up to 1 Gbps, reduced crosstalk.
• Cat6: Up to 10 Gbps at short distances, better shielding.
• Cat6a: 10 Gbps, supports longer distances than Cat6.
• Cat7 / Cat8: For high-performance data centers (10–40 Gbps), expensive.

Single-mode Fiber (SMF): Long-distance transmission (up to 100 km+), uses laser light, thin core (~9µm).

Multi-mode Fiber (MMF): Shorter distance (up to ~2 km), uses LED light, thicker core (~50–62.5µm).

Console (Rollover) Cable: Used to connect PC to router/switch console for CLI access (RJ45 -> DB9/USB).

Crossover Cable (legacy): Used to directly connect two devices; mostly replaced by Auto-MDIX.

1. Physical (L1): Physical medium, raw bits (cables, NICs).
2. Data Link (L2): Frames, MAC addresses, switches. Sub-layers: MAC & LLC.
3. Network (L3): Routing and IP addressing (routers).
4. Transport (L4): Reliable segments (TCP) or fast datagrams (UDP).
5. Session (L5): Manages sessions between devices.
6. Presentation (L6): Translates/encodes data, handles encryption/compression.
7. Application (L7): Protocols apps use (HTTP, SMTP, FTP, DNS).

Mnemonic: Please Do Not Throw Sausage Pizza Away

1. Application: App services (HTTP, DNS, SMTP, etc.).
2. Transport: TCP / UDP.
3. Internet: IP, ICMP, ARP (routing & addressing).
4. Network Access: Physical + Data Link functions (Ethernet, Wi-Fi).

IPv4 example: 192.168.1.1 (32-bit). IPv6 example: 2001:db8::1 (128-bit).

Private IPv4 ranges: 192.168.0.0/16, 10.0.0.0/8, 172.16.0.0–172.31.255.255.

Subnetting divides a network into smaller sub-networks. Example: 192.168.1.0/24 (256 IPs) → 192.168.1.0/25 (128 IPs).

MAC: Hardware address burned into NIC (example: 00:1A:2B:3C:4D:5E) — used on LAN.

IP: Logical address used for routing across networks (example: 192.168.1.100).

DNS converts human-readable domain names (like google.com) into IP addresses. It's the phonebook of the internet.

• HTTP / HTTPS — web browsing
• FTP — file transfers
• SMTP / IMAP / POP3 — email
• DHCP — dynamic IP assignment
• DNS — name resolution
• TCP / UDP — transport

• ping [host]: test reachability (e.g., ping google.com).
• traceroute / tracert: see path packets take to a destination.
• ipconfig / ifconfig / ip a: view IP config.
• nslookup: test DNS resolution.
• netstat: show active connections and listening ports.
• arp -a: view ARP cache.

• Use firewalls to block unauthorized access.
• Keep OS and firmware updated.
• Implement VLANs for segmentation.
• Use strong Wi-Fi encryption (WPA2/WPA3).
• Disable unused ports and services.

Pro tip: remember 80=HTTP, 443=HTTPS, 22=SSH, 21=FTP, 53=DNS.