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Networking fundamentals
Interview questions
Computer networks interview questions
Practise explaining networking concepts clearly, like you would in a real interview.
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02
Networking fundamentals
What do we mean when we call something a network protocol?
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Networking fundamentals
How would you relate the OSI model to the TCP/IP model?
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Networking fundamentals
What happens to application data as it moves down the network stack?
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Networking fundamentals
Can you distinguish a switch, a router, and a gateway?
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Networking fundamentals
What is the difference between bandwidth, throughput, and latency?
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HTTP, HTTPS, and DNS
Walk me through what happens after you enter a URL in a browser.
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HTTP, HTTPS, and DNS
How does DNS resolve a domain name?
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HTTP, HTTPS, and DNS
Does DNS use UDP or TCP?
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HTTP, HTTPS, and DNS
What does HTTPS add on top of HTTP?
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HTTP, HTTPS, and DNS
HTTP is described as stateless. How do websites still maintain a login session?
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HTTP, HTTPS, and DNS
What makes an HTTP method safe or idempotent?
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HTTP, HTTPS, and DNS
What are the practical differences between HTTP/1.1, HTTP/2, and HTTP/3?
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TCP, UDP, and sockets
When would you choose UDP instead of TCP?
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TCP, UDP, and sockets
What is a port number, and why do we need it if we already have an IP address?
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TCP, UDP, and sockets
What exactly is a socket?
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TCP, UDP, and sockets
Why does TCP use a three-way handshake instead of two messages?
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TCP, UDP, and sockets
Why can closing a TCP connection require four messages?
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TCP, UDP, and sockets
How can one web server handle thousands of clients on the same port?
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TCP, UDP, and sockets
If an application sends two messages over TCP, will the receiver read them as two messages?
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TCP, UDP, and sockets
What does it mean when we call UDP connectionless?
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TCP reliability and congestion
How do sequence numbers and acknowledgments make TCP reliable?
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TCP reliability and congestion
How does TCP decide that data should be retransmitted?
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TCP reliability and congestion
What is the difference between flow control and congestion control?
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TCP reliability and congestion
Why is a sliding window faster than sending one packet and waiting for its acknowledgment?
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TCP reliability and congestion
What is TCP slow start trying to achieve?
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TCP reliability and congestion
What is head-of-line blocking in TCP?
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IP addressing and NAT
What are the important differences between IPv4 and IPv6?
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IP addressing and NAT
What is the difference between a public IP address and a private IP address?
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IP addressing and NAT
What does the /24 mean in 192.168.1.0/24?
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IP addressing and NAT
If I split a /24 network into four equal subnets, what prefix will each subnet use?
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IP addressing and NAT
How do NAT and PAT differ?
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IP addressing and NAT
What happens when an IP packet is larger than the path MTU?
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IP addressing and NAT
When does a host send a packet to its default gateway?
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Routing and diagnostics
How does a router choose an entry from its routing table?
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Routing and diagnostics
When would you use static routing instead of a dynamic routing protocol?
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Routing and diagnostics
How do distance-vector and link-state routing protocols differ?
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Routing and diagnostics
What do ping and traceroute actually tell you?
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Routing and diagnostics
Why does an IP packet have a TTL or hop-limit field?
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Ethernet, ARP, and DHCP
What is the difference between a frame, a packet, and a segment?
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Ethernet, ARP, and DHCP
Why does a host need both a MAC address and an IP address?
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Ethernet, ARP, and DHCP
How does an Ethernet switch learn where devices are connected?
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Ethernet, ARP, and DHCP
If I send data to a host on another network, whose MAC address does ARP resolve?
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Ethernet, ARP, and DHCP
Can you explain the DHCP DORA process?
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Ethernet, ARP, and DHCP
How do switches and VLANs affect collision and broadcast domains?
46
Wi-Fi and transmission
Why does Wi-Fi use CSMA/CA instead of the CSMA/CD used by classic shared Ethernet?
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Wi-Fi and transmission
How would you compare the 2.4 GHz, 5 GHz, and 6 GHz Wi-Fi bands?
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Wi-Fi and transmission
Why is measured Wi-Fi throughput usually much lower than the advertised link rate?
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Wi-Fi and transmission
When would fiber be a better choice than copper Ethernet?
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Network security
What does a TLS certificate prove to a browser?
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Network security
What is the difference between a stateful and a stateless firewall?
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Network security
How is an IDS different from an IPS?
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Network security
What does a VPN tunnel provide?
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Network security
Where do symmetric encryption, asymmetric cryptography, and hashing fit in secure communication?
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Practical scenarios
A website works by IP address but not by domain name. What would you check?
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Practical scenarios
A website loads, but it is unusually slow. How would you narrow down the network cause?
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Practical scenarios
You can ping a server, but the application cannot connect to it. What could be wrong?
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Practical scenarios
Users report intermittent packet loss. How would you investigate it?
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Practical scenarios
One device has no Internet access, but other devices on the same network work. What would you check first?
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Practical scenarios