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Computer Networks Interview Questions

TCP behaviour under load, DNS resolution and caching, HTTP semantics and versions, TLS, and the proxy and load balancer layer — weighted toward what breaks in production rather than the OSI model.

TCPDNSHTTPTLSLoad BalancingAria-powered explanations
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9 Easy55 Medium36 Hard

Showing 1–20 of 100

#1Explain the OSI model and how it maps to what actually runs.

Easy
Fundamentals

#2What is the difference between a layer 4 and a layer 7 load balancer?

Medium
Fundamentals

#3What is MTU and what happens when a packet exceeds it?

Hard
Fundamentals

#4What is the difference between a switch, a router, and a hub?

Easy
Fundamentals

#5What is the difference between latency, bandwidth, and throughput?

Medium
Fundamentals

#6What is the bandwidth-delay product and why does it matter?

Hard
Fundamentals

#7What happens when you type a URL into a browser?

Medium
Fundamentals

#8What is NAT and what problems does it cause?

Medium
Fundamentals

#9What is ARP and how does it work?

Medium
Fundamentals

#10What is the difference between IPv4 and IPv6 beyond address length?

Medium
Fundamentals

#11How does subnetting work and what is CIDR notation?

Medium
IP & Routing

#12What is a routing table and how does a router choose a route?

Medium
IP & Routing

#13What is BGP and why does it cause internet outages?

Hard
IP & Routing

#14What is the difference between a private and a public IP address?

Easy
IP & Routing

#15How does traceroute work?

Medium
IP & Routing

#16What is ICMP and why do people block it?

Medium
IP & Routing

#17What is anycast and where is it used?

Hard
IP & Routing

#18What is the difference between unicast, multicast, and broadcast?

Medium
IP & Routing

#19What is a VLAN and why use one?

Medium
IP & Routing

#20What is the difference between a forward proxy and a reverse proxy?

Medium
IP & Routing

Showing 1–20 of 100

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All 100 Computer Networks questions at a glance
  1. Explain the OSI model and how it maps to what actually runs.(Easy)
  2. What is the difference between a layer 4 and a layer 7 load balancer?(Medium)
  3. What is MTU and what happens when a packet exceeds it?(Hard)
  4. What is the difference between a switch, a router, and a hub?(Easy)
  5. What is the difference between latency, bandwidth, and throughput?(Medium)
  6. What is the bandwidth-delay product and why does it matter?(Hard)
  7. What happens when you type a URL into a browser?(Medium)
  8. What is NAT and what problems does it cause?(Medium)
  9. What is ARP and how does it work?(Medium)
  10. What is the difference between IPv4 and IPv6 beyond address length?(Medium)
  11. How does subnetting work and what is CIDR notation?(Medium)
  12. What is a routing table and how does a router choose a route?(Medium)
  13. What is BGP and why does it cause internet outages?(Hard)
  14. What is the difference between a private and a public IP address?(Easy)
  15. How does traceroute work?(Medium)
  16. What is ICMP and why do people block it?(Medium)
  17. What is anycast and where is it used?(Hard)
  18. What is the difference between unicast, multicast, and broadcast?(Medium)
  19. What is a VLAN and why use one?(Medium)
  20. What is the difference between a forward proxy and a reverse proxy?(Medium)
  21. Walk through the TCP three-way handshake and explain why three messages are needed.(Easy)
  22. Why does closing a TCP connection take four messages?(Medium)
  23. What is TIME_WAIT and why does it exist?(Hard)
  24. How does TCP flow control differ from congestion control?(Hard)
  25. Explain TCP slow start and congestion avoidance.(Hard)
  26. What is head-of-line blocking and where does it occur?(Hard)
  27. What is Nagle's algorithm and when should you disable it?(Hard)
  28. What do the different TCP socket states mean operationally?(Hard)
  29. What is the difference between a connection refused and a connection timeout?(Medium)
  30. What is TCP keep-alive and how does it differ from HTTP keep-alive?(Medium)
  31. Why might a TCP connection appear to hang with no error?(Hard)
  32. What is the difference between the SYN backlog and the accept queue?(Hard)
  33. What causes ephemeral port exhaustion and how do you fix it?(Hard)
  34. How does TCP detect and recover from packet loss?(Hard)
  35. What is the difference between TCP and QUIC?(Hard)
  36. What socket options matter for a production server?(Hard)
  37. Why is TCP said to provide a reliable byte stream, and what does that mean for message framing?(Medium)
  38. What is TCP congestion control and how do BBR and CUBIC differ?(Hard)
  39. When would you choose UDP over TCP?(Medium)
  40. What guarantees does UDP actually provide?(Easy)
  41. Why does DNS use UDP, and when does it use TCP?(Medium)
  42. What is a UDP amplification attack?(Hard)
  43. How do you build reliability on top of UDP if you need it?(Hard)
  44. What is the maximum practical UDP payload size and why does it matter?(Medium)
  45. Walk through a full DNS resolution.(Medium)
  46. What are the main DNS record types and what is each for?(Medium)
  47. How does DNS TTL affect deployments and failover?(Medium)
  48. What is the difference between a recursive and an authoritative DNS server?(Medium)
  49. What is DNS round-robin and why is it a poor load balancer?(Medium)
  50. What is DNS caching at each layer, and how does it cause stale-address bugs?(Hard)
  51. What is DNS over HTTPS and what does it change?(Hard)
  52. What does dig show you and how do you read it?(Medium)
  53. What is split-horizon DNS?(Medium)
  54. Why might a service be reachable by IP but not by hostname?(Medium)
  55. What is the difference between HTTP/1.1, HTTP/2, and HTTP/3?(Medium)
  56. What makes an HTTP method safe, idempotent, or cacheable?(Medium)
  57. Explain the main HTTP status code families and the ones that matter most.(Easy)
  58. What is the difference between a 502, 503, and 504?(Medium)
  59. How does HTTP caching work?(Medium)
  60. What is CORS and what problem does it solve?(Medium)
  61. What is the difference between cookies, localStorage, and sessionStorage?(Medium)
  62. What is chunked transfer encoding and when is it used?(Hard)
  63. How do WebSockets differ from HTTP long polling and Server-Sent Events?(Medium)
  64. What does the Content-Type header do and why does charset matter?(Easy)
  65. What are the important HTTP security headers?(Medium)
  66. What is the difference between authentication and authorization in HTTP, and which status codes apply?(Medium)
  67. How does HTTP connection reuse work and why does it matter so much?(Medium)
  68. What is HTTP request smuggling?(Hard)
  69. What is the difference between Content-Length and Transfer-Encoding, and can you use both?(Hard)
  70. How should a client implement retries safely?(Medium)
  71. What is the difference between a 301 and a 302 redirect, and why does it matter?(Medium)
  72. What is the difference between an ETag and Last-Modified?(Medium)
  73. Walk through the TLS handshake.(Hard)
  74. How does certificate validation work and what is a chain of trust?(Medium)
  75. What is SNI and why does it matter?(Medium)
  76. What is mutual TLS and when would you use it?(Hard)
  77. What is forward secrecy?(Hard)
  78. What is the difference between encryption, hashing, and encoding?(Easy)
  79. How does HTTPS protect against a man-in-the-middle attack?(Medium)
  80. What is TLS termination and where should it happen?(Medium)
  81. Why might a TLS connection fail from a service but work in a browser?(Hard)
  82. What is certificate pinning and why is it discouraged now?(Hard)
  83. What load balancing algorithms are there and when does each fit?(Medium)
  84. What is consistent hashing and what problem does it solve?(Hard)
  85. How should health checks be designed?(Medium)
  86. What is a circuit breaker and how does it differ from a retry?(Medium)
  87. What is X-Forwarded-For and how should it be handled safely?(Hard)
  88. How do you achieve session affinity, and why is it often a bad idea?(Medium)
  89. What is a service mesh and what does it do for networking?(Hard)
  90. How would you design rate limiting?(Hard)
  91. A service is intermittently slow. How do you determine whether the network is responsible?(Hard)
  92. What do you use tcpdump for and how do you read a capture?(Hard)
  93. What is the difference between ping, telnet, curl, and nc for connectivity testing?(Medium)
  94. How do you debug a connection that works from one machine but not another?(Medium)
  95. What is bufferbloat?(Hard)
  96. Why do timeouts need to be configured at every layer, and how should you choose them?(Medium)
  97. What causes a thundering herd, and how do you prevent it?(Medium)
  98. How does a CDN work and what should you be careful about?(Medium)
  99. What is the difference between a stateful and a stateless firewall?(Medium)
  100. What networking knowledge actually matters for a backend engineer?(Easy)