Osi & Tcp Ip Models
Explain the OSI 7-layer model and give a practical example of a protocol at each layer.
What is the difference between a Frame, a Packet, and a Segment in terms of the networking stack?
Explain the lifecycle of a network request from a client to a server.
Explain every networking step that occurs from the moment you type a URL into a browser and hit Enter until the page begins to render.
Describe the process of data encapsulation and decapsulation as a packet moves from the Application layer down to the Physical layer.
What are the primary differences between the OSI 7-layer model and the TCP/IP 4-layer model, and why do we use both?
Network Devices & Topologies
Explain the difference between a Hub, a Switch, and a Router.
Explain the difference between a switch and a router in terms of the OSI model.
Explain the OSI 7-layer model. Which layers do a router and a switch typically operate on, and why?
What is the difference between full-duplex and half-duplex communication?
What is a modem, and what does it do that a router does not?
What is a NIC (Network Interface Card), and at which layers does it operate?
What is the difference between a repeater, a bridge, and a switch?
What are the differences between LAN, WAN, MAN, and PAN?
What is the difference between a client-server and a peer-to-peer network architecture?
Compare star, bus, ring, and mesh network topologies and their tradeoffs.
What is the difference between a collision domain and a broadcast domain?
What is the difference between Unicast, Broadcast, Multicast, and Anycast?
What is the difference between a Layer 2 switch and a Layer 3 switch?
Switching & Layer 2
What is the structure of a MAC address, and what is the significance of the OUI portion?
How does a machine find the MAC address of another machine on the same local network? Explain the ARP request/reply flow.
Why do we need both MAC addresses and IP addresses? Could a network function with only one of them?
What is a VLAN, and how does it help segment a network at Layer 2?
What is trunking (802.1Q tagging), and why is it needed between switches?
What is the difference between CSMA/CD and CSMA/CA, and why is one used in wired Ethernet and the other in Wi-Fi?
How does the data-link layer detect transmission errors using a CRC or checksum?
Can you describe the structure of an Ethernet frame and what its main fields are?
What is the Spanning Tree Protocol (STP), and what problem does it prevent in a switched network?
What is a broadcast storm, and how can it occur in a switched network?
Transport Layer Fundamentals
What are the key differences between TCP and UDP, and when would you choose one over the other?
What is a network socket, and what is the relationship between an IP address, a port, and a socket?
What are some well-known port numbers, and why are ports below 1024 treated specially?
What is the difference between a connection-oriented and a connectionless protocol?
When would you choose UDP over TCP for a real-time application, and what specific reliability features do you lose?
What is multiplexing and demultiplexing at the transport layer, and how are port numbers used to achieve it?
Tcp Reliability & Flow Control
What is the 'Sliding Window' in TCP, and how does it relate to flow control?
How does TCP ensure reliability? Explain sequence numbers and acknowledgments.
Describe the 'Slow Start' phase of TCP congestion control. Why is it used?
Explain the difference between Flow Control and Congestion Control in TCP. How does 'Slow Start' work?
What causes packet loss in a network, and how does TCP react to it?
Explain the difference between TCP flow control (sliding window) and congestion control (slow start/AIMD), and what problem each is trying to solve.
Explain TCP Congestion Control. What are 'Slow Start' and 'Congestion Avoidance'?
How does TCP decide when to retransmit a packet? Explain the role of the Retransmission Timeout (RTO).
What are fast retransmit and fast recovery in TCP, and how do duplicate ACKs trigger them?
What is Nagle's algorithm, and what problem does it solve in TCP?
Explain AIMD (Additive Increase, Multiplicative Decrease) and its role in TCP congestion control.
Tcp Connection Lifecycle
Walk me through the TCP three-way handshake. Why are three steps necessary instead of two?
Why does a TCP connection require a 4-way handshake to close instead of just 3, and what is the TIME_WAIT state?
What is 'Round Trip Time' (RTT), and how does it affect the performance of the TCP handshake?
Walk through the steps of the TCP three-way handshake. What happens if the final ACK is lost?
What is 'Head-of-Line (HOL) Blocking' in the context of a TCP connection?
What is Head-of-Line (HOL) Blocking and how do HTTP/2 and HTTP/3 address it differently?
Ip Addressing & Subnetting
What is the difference between a Public IP and a Private IP (RFC 1918)? How do they communicate with each other?
What is the purpose of a subnet mask and CIDR notation?
What is the 'TTL' (Time to Live) field in an IP packet and what happens when it reaches zero?
What is a subnet mask, and how does a router use it to determine if a destination IP is on the local network or needs to be routed externally?
How does IP fragmentation and reassembly work, and why is fragmentation generally undesirable?
How many usable host addresses are available in a /26 subnet, and how do you calculate that?
Aside from the address space size, what are the key structural differences between an IPv4 header and an IPv6 header?
What are the different types of IPv6 addresses, and how does SLAAC allow a host to auto-configure an address?
Routing & Forwarding
How does a router decide where to send a packet? Explain the concept of a routing table.
What is a default gateway, and what role does it play when a host sends traffic off its local network?
What is the fundamental difference between circuit switching and packet switching, and which one does the modern internet use and why?
What is the difference between static and dynamic routing, and when would you use each?
What is Anycast routing, and how is it used to reduce latency for services like DNS or globally distributed APIs?
Explain the concept of BGP (Border Gateway Protocol) in the context of how the Internet routes traffic between providers.
What is the difference between distance-vector and link-state routing protocols, using RIP and OSPF as examples?
What is the difference between routing and forwarding within a router?
Dhcp & Network Services
What is SSH, and what does it provide at the application layer?
What is Telnet, and why is it considered insecure compared to SSH?
What are the main differences between SMTP, IMAP, and POP3 in how email is sent and retrieved?
What is the difference between FTP and SFTP, and what is the difference between active and passive FTP?
What is NTP used for, and why is time synchronization important in a network?
What is SNMP, and how is it used for network management and monitoring?
How does DHCP assign IP addresses to devices? Walk me through the DORA process.
Dns
What are the most common DNS record types (A, AAAA, CNAME, MX, TXT) and what do they do?
What do NS and TXT records do in DNS?
Explain the DNS resolution process. What is the difference between a Recursive and an Iterative query?
What is the difference between an A record, a CNAME record, and an ALIAS record, and when would you use one over the other?
Describe the step-by-step process of a recursive DNS lookup, starting from the browser cache to the authoritative nameserver.
How do DNS caching and TTL values work, and what are the tradeoffs of a long vs short TTL?
Describe the DNS server hierarchy, root servers, TLD servers, and authoritative servers, and their roles.
What is a PTR record and how is reverse DNS lookup used?
How does round-robin DNS work as a basic load-distribution mechanism?
What is DNS Spoofing (or Cache Poisoning), and how can it be prevented?
Http & Web Protocols
What is the purpose of the 'Host' header in an HTTP request?
What are the categories of HTTP status codes (1xx–5xx) at the protocol level, and give an example of each?
How is an HTTP request structured, the request line, headers, and body?
How does the WebSocket 'Upgrade' handshake work? Once established, how does it differ from a standard HTTP persistent connection?
How do HTTP Cookies work at the protocol level (headers) to maintain state in a stateless protocol?
Explain the differences between HTTP/1.1, HTTP/2, and HTTP/3. Why did the industry move toward each version?
From a networking perspective, what are the primary differences between gRPC and REST?
What is the difference between HTTP/1.1 and HTTP/2? How does multiplexing work in HTTP/2?
How do WebSockets work, and how does the Upgrade handshake transition from HTTP?
Explain the difference between WebSockets, Long Polling, and Server-Sent Events (SSE). When would you choose one over the others?
Explain the difference between a 301 and a 302/307 redirect at the protocol level.
At the protocol level, what is the difference between a 'Safe' method and an 'Idempotent' method?
What is the purpose of the Connection: keep-alive header, and how does it affect the underlying TCP connection?
Why does HTTP/3 use UDP (via QUIC) instead of TCP? How does it ensure reliability if UDP is inherently unreliable?
How does HTTP/2's multiplexing differ from HTTP/1.1's pipelining, and why does HTTP/3 move from TCP to QUIC (UDP)?
Compare HTTP/1.1, HTTP/2, and HTTP/3. Specifically, how does HTTP/3 solve the 'TCP Head-of-Line blocking' problem found in HTTP/2?
Security & Encryption
What is the role of a Certificate Authority (CA) and a digital certificate in network security?
In a TLS handshake, how are asymmetric and symmetric encryption used together to secure a connection?
How does a Man-in-the-Middle attack work on an unencrypted network, and how does TLS/SSL prevent this?
What is 'TLS Termination' at the load balancer level, and why is it used?
How does a VPN (Virtual Private Network) create a secure 'tunnel' over the public internet?
Explain how an HTTPS connection is established. What happens during the TLS handshake?
What is the difference between Symmetric and Asymmetric encryption within the context of a TLS session?
Explain the TLS 1.3 handshake. How does it differ from TLS 1.2 in terms of performance and security?
How does the use of a Certificate Authority (CA) and Digital Signatures prevent a Man-in-the-Middle attack during a TLS handshake?
What is a cipher suite in TLS, and what components does it specify?
How does IPsec secure traffic, and what is the difference between transport mode and tunnel mode?
Network Attacks & Defense
How does a stateful firewall track connections compared to a simple packet-filtering (stateless) firewall?
What is a DMZ (Demilitarized Zone) and why would a company use one?
How does a Man-in-the-Middle (MITM) attack work at the network level?
What is ARP spoofing (ARP poisoning), and how can an attacker use it to intercept traffic?
What is a DDoS attack, and how do volumetric, protocol, and application-layer attacks differ?
What is packet sniffing, and how can traffic be captured on a network?
Explain the SYN flood attack. How does it exploit the TCP handshake?
What is a TCP SYN flood attack, and how do 'SYN Cookies' help mitigate it?
Performance & Quality Of Service
Explain the relationship between Latency and Throughput. Can you have high throughput with high latency?
What is the difference between bandwidth, throughput, and latency?
What are Latency, Throughput, and Jitter? How do they impact a VoIP application vs. a file download?
Define Round Trip Time (RTT) and Jitter, and explain how high jitter affects a VoIP or video streaming application specifically.
How does the physical distance between a client and server impact the RTT, and why is this critical for protocols like TCP?
What is Quality of Service (QoS), and what mechanisms are used to prioritize certain traffic?
What is Maximum Transmission Unit (MTU), and what happens at the network layer if a packet is larger than the MTU of a hop along its path?
What is the Bandwidth-Delay Product, and why does it matter when tuning TCP performance for long-distance high-speed links?
Nat Proxies & Load Balancing
Explain the conceptual difference between a forward proxy and a reverse proxy, and which one is typically used to protect a web server.
How does the 'ping' command work? Which protocol does it use and at which layer?
What is the difference between a Layer 4 (Transport) and a Layer 7 (Application) load balancer, and what information can an L7 balancer see that an L4 balancer cannot?
What is NAT (Network Address Translation), and why is it necessary for the modern internet?
How do tools like ping and traceroute work at the protocol level, and what specific field in the IP header does traceroute manipulate?
Explain how Network Address Translation (NAT) allows multiple devices in a private network to share a single public IP address, and what role port numbers play in this process.
What are 'Sticky Sessions' (Session Affinity) and what are the tradeoffs of using them in a networked environment?
What is the difference between NAT and PAT (Port Address Translation)?