Networking Basics

IP, TCP, UDP, DNS, HTTP, HTTPS and TLS, ports and sockets, latency, bandwidth and throughput, firewalls, proxies and load balancers.

1. Walk me through what happens, at the network level, when a .NET client calls https://api.example.com/orders/42 and gets a response.

   An end-to-end tour of one HTTPS request: DNS, IP routing, ports, TCP handshake, TLS, HTTP, load balancers and proxies, connection reuse, and where time goes.

   Intermediate Theory Networking Basics · 🔗 3 follow-ups
2. What is an IP address? Explain IPv4 vs IPv6, private vs public ranges, subnets and CIDR notation, and NAT, with examples from cloud or container networking.

   IP addressing fundamentals: IPv4 and IPv6, CIDR and subnet sizing, private, loopback and link-local ranges, NAT, and how they show up in cloud VNets and Kubernetes.

   Junior Theory Networking Basics · 🔗 2 follow-ups
3. What is the difference between TCP and UDP? When would you choose each, and why does HTTP/3 run over UDP?

   TCP and UDP compared: connections, reliability, ordering, flow and congestion control, head-of-line blocking, typical uses, and QUIC/HTTP/3 in .NET.

   Mid-Level Theory Networking Basics · 🔗 3 follow-ups · 🛠 1 real-world
4. What are ports and sockets? Your ASP.NET Core API works on your laptop but nothing answers when you run it in Docker. What is going on?

   Ports, listening vs connected sockets, the 4-tuple, binding to localhost vs all interfaces, container port mapping, and tools to see who is listening.

   Mid-Level Debugging Networking Basics · 🔗 3 follow-ups · 🛠 1 real-world
5. How does DNS resolution work? Describe a DNS-related incident you could see in a .NET service in Kubernetes or the cloud, and how you would diagnose it.

   DNS records, recursive resolution, TTLs and caching, how .NET resolves names, connection pooling vs DNS changes, Kubernetes ndots and conntrack issues, and diagnosis tools.

   Senior Debugging Networking Basics · 🔗 3 follow-ups · 🛠 1 real-world
6. Explain HTTP from a backend engineer's point of view: methods and idempotency, status codes, important headers, and the practical differences between HTTP/1.1, HTTP/2 and HTTP/3.

   HTTP semantics for API design and operations: safe and idempotent methods, status code classes, caching and content headers, and the evolution from HTTP/1.1 to HTTP/2 and HTTP/3.

   Mid-Level Theory Networking Basics · 🔗 3 follow-ups · 🛠 1 real-world
7. How do HTTPS and TLS work? Walk through the TLS 1.3 handshake and certificate validation, and explain how you would fix "The remote certificate is invalid" errors in a .NET service without disabling validation.

   TLS goals, the TLS 1.3 handshake, certificate chains and validation, SNI and ALPN, mutual TLS, and safe diagnosis of certificate errors in .NET.

   Senior Security Networking Basics · 🔗 3 follow-ups · 🛠 1 real-world
8. What is the difference between latency, bandwidth and throughput? How do round-trip time and chatty communication affect a .NET service, and how would you improve it?

   Latency, bandwidth and throughput defined; RTT, bandwidth-delay product, Little's law and tail latency; why chatty calls across regions hurt and how batching, caching and placement fix it.

   Senior Theory Networking Basics · 🔗 3 follow-ups · 🛠 1 real-world
9. How do firewalls, security groups and network policies work? A .NET service cannot reach a dependency, or its connections drop after being idle. How do you troubleshoot it?

   Stateful vs stateless firewalls, cloud NSGs/security groups, NACLs, WAFs, Kubernetes NetworkPolicy, idle timeouts, and a step-by-step connectivity troubleshooting method.

   Mid-Level Debugging Networking Basics · 🔗 3 follow-ups · 🛠 1 real-world
10. What is the difference between a forward proxy and a reverse proxy? Your ASP.NET Core app behind a reverse proxy logs the proxy's IP for every user and gets into an HTTPS redirect loop. What is wrong and how do you fix it safely?

    Forward vs reverse proxies, what they change (TLS, headers, timeouts, buffering), X-Forwarded-* headers and the ForwardedHeaders middleware, outbound proxy settings, and spoofing risks.

    Senior Debugging Networking Basics · 🔗 3 follow-ups · 🛠 1 real-world
11. How do load balancers work? Compare layer 4 and layer 7 load balancing, explain health checks, algorithms, sticky sessions and connection draining, and why gRPC traffic can end up on only one pod.

    L4 vs L7 load balancing, balancing algorithms, health checks and readiness, session affinity, graceful shutdown and draining, global load balancing, and long-lived HTTP/2 connection imbalance.

    Senior SystemDesign Networking Basics · 🔗 3 follow-ups · 🛠 1 real-world
12. Design the network path for a public .NET API on a cloud platform: from the user's browser to the database. Which components do you put in the path (DNS, CDN/WAF, load balancers, proxies, firewalls, private networking), and what does each one do?

    An end-to-end cloud network design for a public API: global entry, TLS, WAF, L7 routing, private subnets, egress control, private endpoints, and how each choice affects security, latency and operations.

    Staff / Architect SystemDesign Networking Basics · 🔗 3 follow-ups · 🛠 1 real-world