Networking Interview Questions

3 questions for junior Networking interviews, with model answers, code examples and common mistakes. Answer each one out loud first, then reveal the answer.

3questions

1level

HTTP Methods and Status Codes

// interview question

What are the main HTTP methods and what do common status codes like 200, 404, and 500 mean?

Sample answer

The main HTTP methods are: GET (retrieve data), POST (create data), PUT (update/replace data), PATCH (partial update), and DELETE (remove data). Status code 200 means success, 201 means created, 301/302 are redirects, 400 is bad request, 401 is unauthorized, 403 is forbidden, 404 is not found, and 500 is internal server error. Understanding these is essential for API troubleshooting.

Why this matters

HTTP is the foundation of web communication. DevOps engineers troubleshoot APIs, configure load balancers, set up monitoring, and read access logs daily. Knowing HTTP methods and status codes helps quickly diagnose issues and communicate with developers effectively.

Code examples

Test HTTP endpoints with curl

bash

# GET request
curl -X GET https://api.example.com/users

# POST request with JSON data
curl -X POST https://api.example.com/users \
  -H 'Content-Type: application/json' \
  -d '{"name": "John"}'

# Check response headers and status
curl -I https://example.com

# Verbose output for debugging
curl -v https://example.com

Common mistakes to avoid

Using GET requests to modify data
Not checking response status codes in scripts
Confusing 401 (authentication) with 403 (authorization)

Likely follow-ups

What is the difference between PUT and PATCH?
What does a 502 Bad Gateway error typically indicate?
What is the difference between 401 and 403 status codes?

Answer out loud first, then check yourself against the model answer.

Juniorbeginner

DNS Basics

// interview question

What is DNS and how does the DNS resolution process work step by step?

Sample answer

DNS (Domain Name System) translates human-readable domain names to IP addresses. Resolution flow: browser cache → OS cache → resolver (ISP/configured DNS) → root servers → TLD servers → authoritative nameservers. Common record types: A (IPv4), AAAA (IPv6), CNAME (alias), MX (mail), TXT (verification).

Why this matters

DNS is fundamental to how the internet works. DevOps engineers need to understand DNS for configuring domains, troubleshooting connectivity issues, setting up load balancers, managing SSL certificates, and configuring email services.

Code examples

DNS troubleshooting commands

bash

# Query DNS records
dig example.com
dig example.com MX
dig +short example.com A

# Alternative tool
nslookup example.com

# Trace DNS resolution path
dig +trace example.com

# Check specific nameserver
dig @8.8.8.8 example.com

Local DNS configuration

bash

# View DNS resolver config
cat /etc/resolv.conf

# Local hosts file (bypasses DNS)
cat /etc/hosts
# 127.0.0.1   localhost
# 192.168.1.10   myapp.local

# Flush DNS cache (varies by OS)
# macOS
dscacheutil -flushcache
# Linux systemd
sudo systemd-resolve --flush-caches

Common mistakes to avoid

Forgetting about DNS caching when making changes (TTL)
Using CNAME at the apex/root domain (not allowed)
Not understanding DNS propagation delays

Likely follow-ups

What's the difference between A records and CNAME records?
What is TTL and why does it matter?
How would you set up DNS for a load-balanced application?

Answer out loud first, then check yourself against the model answer.

Juniorbeginner

TCP/IP Fundamentals

// interview question

Explain the difference between TCP and UDP. When would you use each?

Sample answer

TCP (Transmission Control Protocol) is connection-oriented, ensuring reliable, ordered delivery with error checking and retransmission. UDP (User Datagram Protocol) is connectionless, offering faster but unreliable delivery without guarantees. Use TCP for web traffic (HTTP), file transfers, and email. Use UDP for streaming, gaming, DNS queries, and real-time applications where speed matters more than reliability.

Why this matters

Understanding TCP vs UDP is fundamental for troubleshooting network issues, configuring firewalls, and designing distributed systems. DevOps engineers must know which protocol applications use to properly monitor, secure, and optimize network traffic.

Code examples

Check open TCP/UDP ports

bash

# List all TCP connections
netstat -tulpn | grep tcp
ss -tulpn | grep tcp

# List all UDP connections
netstat -tulpn | grep udp
ss -tulpn | grep udp

# Test TCP connectivity
nc -zv hostname 80

# Test UDP connectivity
nc -zuv hostname 53

Common mistakes to avoid

Assuming all network traffic uses TCP
Blocking UDP on firewalls without understanding impact on DNS and NTP
Not considering TCP overhead for high-throughput applications

Likely follow-ups

What is the TCP three-way handshake?
Why does DNS use UDP by default but can fall back to TCP?
What are the common TCP states and what do they mean?

Answer out loud first, then check yourself against the model answer.

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Networking Interview Questions

HTTP Methods and Status Codes

DNS Basics

TCP/IP Fundamentals

More interview topics

Also worth your time on this topic

UDP vs TCP: How Much Faster Is UDP Really?

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