Networking Interview – Top 30 Q&A (2025)

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L1 Basics:

1. What is an IP address?

  • Unique device identifier in a network.
  • Command: `ip addr` (Linux) or `ipconfig` (Windows).

2. Difference: Public vs Private IP?

  • Public = internet-facing, Private = internal use.
  • Command: Check public IP with curl ifconfig.me.

3. What is a Subnet Mask?

  • Defines network & host portions in IP.
  • Command: `ifconfig` (Linux) or `ipconfig /all` (Windows).

4. What is a Default Gateway?

  • Device routing traffic outside local network.
  • Command: `route -n` (Linux) or `netstat -r` (Windows).

5. OSI Layers?

  • 7 — Physical to Application.
  • Tool: Wireshark for layer analysis.

6. What is a Switch?

  • Connects devices in a LAN.
  • Command: `arp -a` to see connected devices.

7. What is a Router?

  • Routes data between networks.
  • Command: `traceroute google.com` (Linux) or `tracert google.com` (Windows).

8. What is DNS?

  • Translates domain names to IP.
  • Command: `nslookup example.com` or dig example.com.

9. What is DHCP?

  • Auto-assigns IP to devices.
  • Command: `dhclient` (Linux) or `ipconfig /release & renew` (Windows).

10. Ping command use?

  • Checks host availability & latency.
  • Command: ping google.com.

L2 Intermediate:

11. What is VLAN?

  • Virtual LAN for segmenting networks.
  • Command: `vconfig` (Linux VLAN setup).

12. What is Trunk Port?

  • Carries multiple VLANs.
  • Tool: Cisco IOS switchport mode trunk.

13. Difference: TCP vs UDP?

  • TCP = reliable, UDP = fast/unreliable.
  • Command: Test with `nc -vz` (TCP) vs `nc -u` (UDP).

14. What is Port Security?

  • Restricts switch port access.
  • Tool: Cisco switchport port-security.

15. What is ARP?

  • Resolves IP to MAC.
  • Command: `arp -a` (Windows/Linux).

16. What is a MAC address?

  • Unique NIC hardware ID.
  • Command: `ip link show` (Linux) or `getmac` (Windows).

17. What is NAT?

  • Translates private to public IP.
  • Tool: `iptables` for Linux NAT rules.

18. What is PAT?

  • Many private IPs to one public IP.
  • Tool: Cisco ip nat inside source list.

19. What is STP?

  • Prevents loops in switching.
  • Command: `show spanning-tree` (Cisco).

20. Traceroute purpose?

  • Path check to destination.
  • Command: `traceroute google.com` or `pathping` (Windows).

L3 Advanced:

21. What is BGP?

  • Path vector routing protocol.
  • Command: `show ip bgp` (Cisco).

22. Difference: Static vs Dynamic Routing?

  • Static = manual, Dynamic = auto updates.
  • Tool: OSPF (router ospf 1).

23. What is OSPF?

  • Link-state routing protocol.
  • Command: show ip ospf neighbor.

24. Difference: IPv4 vs IPv6?

  • 32-bit vs 128-bit addressing.
  • Command: `ping6` for IPv6 testing.

25. What is ACL?

  • Packet filtering rule set.
  • Tool: iptables -A INPUT -p tcp --dport 22 -j ACCEPT.

26. What is Port Forwarding?

27. What is a VPN?

  • Secure private network over internet.
  • Tool: OpenVPN (openvpn --config client.ovpn).

28. Difference: Site-to-Site vs Remote Access VPN?

  • Office-office vs user-office secure tunnels.
  • Tool: WireGuard (wg-quick up wg0).

29. What is QoS?

  • Traffic priority management.
  • Command: Linux `tc` (Traffic Control).

30. What is a Load Balancer?

  • Distributes traffic across servers.
  • Tool: Nginx (upstream backend {}).

You Should Know:

Practical Networking Commands

  • Scan Open Ports: `nmap -sV 192.168.1.1`
  • Check Routing Table: `netstat -rn`
  • Test Bandwidth: `iperf3 -c server_ip`
  • Capture Packets: `tcpdump -i eth0 -w capture.pcap`
  • Check SSL Cert: `openssl s_client -connect example.com:443`

Linux Network Config

 Set Static IP 
nmcli con mod eth0 ipv4.addresses 192.168.1.10/24 
nmcli con mod eth0 ipv4.gateway 192.168.1.1 
nmcli con up eth0

Windows Network Troubleshooting

 Reset TCP/IP Stack 
netsh int ip reset 
 Flush DNS 
ipconfig /flushdns

What Undercode Say

Networking remains the backbone of cybersecurity. Mastering these concepts ensures robust infrastructure defense. Future networks will rely more on IPv6, AI-driven routing, and zero-trust architectures. Automation (Ansible, Python scripts) will dominate network management.

Prediction

By 2026, SDN (Software-Defined Networking) and AI-based traffic analysis will replace traditional routing protocols. Quantum networking may disrupt encryption standards.

Expected Output:

A structured networking guide with practical commands for interviews and real-world implementation.

References:

Reported By: Muhammad Hameez – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅

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