What is the TCP three-way handshake?
Answer: SYN → SYN-ACK → ACK establishes a connection.
Explanation
Connections close with FIN/ACK exchanges.
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Computer Networks: Fundamentals (University)
TransportToolsWirelessPerformanceSecurityApplicationModelsNetworkPhysical/link
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Transport
What ports do HTTP, HTTPS, SSH, DNS, SMTP, and FTP use?
Answer: HTTP 80, HTTPS 443, SSH 22, DNS 53, SMTP 25, FTP 21.
Explanation
Also: DHCP 67/68, RDP 3389.
What are port numbers for?
Answer: They identify the application or service on a host; combined with the IP address they form a socket.
Explanation
Well-known ports: 0–1023.
TCP vs UDP?
Answer: TCP: connection-oriented, reliable, ordered, with flow and congestion control. UDP: connectionless, no guarantees, lower overhead.
Explanation
TCP for web and email; UDP for video, DNS, gaming.
Tools
What do ping, traceroute, and nslookup do?
Answer: ping tests reachability and round-trip time; traceroute shows the path of routers; nslookup queries DNS.
Explanation
netstat shows active connections.
Wireless
What are common Wi-Fi standards and bands?
Answer: 802.11 a/b/g/n/ac/ax (Wi-Fi 6); bands 2.4 GHz (longer range) and 5 GHz (faster, shorter range).
Explanation
WPA3 is the current security standard.
Performance
What does a CDN do?
Answer: Caches content on servers close to users to reduce latency and origin load.
Explanation
Examples: Cloudflare, Akamai.
Bandwidth vs latency?
Answer: Bandwidth is the maximum data rate; latency is the delay for data to travel from source to destination.
Explanation
High bandwidth does not fix high latency.
Security
What is a DDoS attack?
Answer: Overwhelming a target with traffic from many sources to make it unavailable.
Explanation
Mitigated by rate limiting, scrubbing services, and CDNs.
What is a man-in-the-middle attack?
Answer: An attacker secretly intercepts and possibly alters communication between two parties.
Explanation
TLS with certificate validation defends against it.
What is a VPN?
Answer: An encrypted tunnel over a public network that makes remote traffic appear to come from the private network.
Explanation
Common protocols: IPsec, WireGuard, OpenVPN.
What is a firewall?
Answer: A device or software that filters traffic based on rules (addresses, ports, protocols, or application state).
Explanation
Stateful firewalls track connections.
Application
What is the difference between HTTP GET and POST?
Answer: GET retrieves data with parameters in the URL; POST sends data in the body, typically to create or change something.
Explanation
GET should be idempotent.
How does HTTPS secure HTTP?
Answer: It runs HTTP over TLS, encrypting the connection and authenticating the server with a certificate.
Explanation
Certificates are issued by certificate authorities.
What does DHCP do?
Answer: Automatically assigns IP addresses and network settings to devices.
Explanation
DORA: Discover, Offer, Request, Acknowledge.
What does DNS do?
Answer: Translates domain names to IP addresses through a hierarchy of resolvers, root, TLD, and authoritative servers.
Explanation
Record types: A, AAAA, CNAME, MX, TXT.
Models
What are the seven layers of the OSI model?
Answer: Physical, Data Link, Network, Transport, Session, Presentation, Application.
Explanation
Mnemonic: Please Do Not Throw Sausage Pizza Away.
What is encapsulation?
Answer: Each layer adds its own header to data from the layer above as it moves down the stack.
Explanation
Reversed (decapsulation) at the receiver.
How does the TCP/IP model map to OSI?
Answer: Link (physical + data link), Internet (network), Transport, Application (session + presentation + application).
Explanation
Four layers instead of seven.
Network
What is ICMP used for?
Answer: Diagnostic and error messages, such as ping (echo) and traceroute.
Explanation
Not used to carry application data.
Static vs dynamic routing?
Answer: Static routes are configured manually; dynamic routing protocols (OSPF, BGP, RIP) exchange route information automatically.
Explanation
BGP routes between autonomous systems on the internet.
What does a router do?
Answer: Forwards packets between networks using IP addresses and a routing table.
Explanation
Operates at Layer 3.
What does NAT do?
Answer: Translates private addresses to a public address so many devices share one public IP.
Explanation
Port address translation tracks connections by port.
What are private IP ranges?
Answer: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16.
Explanation
Not routable on the public internet; used behind NAT.
What does a subnet mask do?
Answer: Separates the network portion of an IP address from the host portion.
Explanation
/24 = 255.255.255.0 = 254 usable hosts.
What is an IP address and how do IPv4 and IPv6 differ?
Answer: A logical address for routing between networks; IPv4 is 32-bit (dotted decimal), IPv6 is 128-bit (hexadecimal).
Explanation
IPv6 solves IPv4 address exhaustion.
Physical/link
What is a VLAN?
Answer: A virtual LAN that segments a physical switch into separate broadcast domains.
Explanation
Tagged with 802.1Q.
What is ARP?
Answer: Address Resolution Protocol maps an IP address to a MAC address on the local network.
Explanation
Cached in the ARP table.
What does a switch do?
Answer: Forwards frames based on MAC addresses, learning which port each device is on.
Explanation
Operates at Layer 2; a hub just repeats to all ports.
What is a MAC address?
Answer: A 48-bit hardware address burned into a network interface, used for delivery within a local network.
Explanation
Written as six hexadecimal pairs.
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