OSI vs TCP/IP
OSI: 7 layers (physical→application). TCP/IP: 4 layers (link, internet, transport, application). Practical networking references TCP/IP.
TCP vs UDP
TCP: reliable, ordered, congestion control. UDP: faster, no guarantees. Use TCP for web/API; UDP for streaming/DNS/gaming.
HTTP basics
Methods: GET/POST/PUT/PATCH/DELETE. Status codes: 2xx, 3xx, 4xx, 5xx. Headers, cookies, caching, content negotiation.
TLS/SSL
Encrypts data in transit; uses certs and handshakes to derive session keys. Prevents MITM and snooping.
DNS and record types
DNS maps names to IPs. Records: A/AAAA (address), CNAME (alias), MX (mail), TXT, NS, SOA.
Routing and NAT
Routers forward packets based on routes. NAT translates private IPs to public. Use CIDR blocks; private ranges: 10.0.0.0/8, 172.16/12, 192.168/16.
WebSockets vs HTTP/2/3
WebSockets: full-duplex. HTTP/2: multiplexing over one TCP connection. HTTP/3: QUIC over UDP reducing head-of-line blocking.
CIDR and subnetting
Calculate network/host ranges using CIDR notation; understand masks, subnet sizes, and reserved addresses.
TCP 3-way handshake
SYN → SYN-ACK → ACK establishes a connection; includes sequence numbers and window sizes for flow control.
Congestion control
Algorithms like Reno/CUBIC adjust sending rate based on loss/latency to avoid network saturation.
VPN vs Direct Connect
VPNs encrypt over the internet; Direct Connect provides private dedicated links to cloud providers with consistent latency.
IPv6 basics
Larger address space, simplified headers, stateless autoconfiguration; dual-stack deployments coexist with IPv4.