What is an IP Address?
Learn what an IP address is, IPv4 vs IPv6, public vs private ranges, and how routers use it — with networking interview questions answered.
Expected Interview Answer
An IP address is a numeric label assigned to every device on a network so it can be uniquely identified and reached — IPv4 uses a 32-bit address written as four dotted decimal numbers, while IPv6 uses a 128-bit address written in hexadecimal groups.
Every packet on the internet carries a source and destination IP address, which routers use to forward it toward the right network and, ultimately, the right host — the same job a postal address does for a letter. IPv4 addresses (e.g., 192.168.1.10) are split into a network portion and a host portion via a subnet mask, and the roughly 4.3 billion possible addresses are now scarce, which is why NAT and IPv6 exist. IPv6 (e.g., 2001:db8::1) expands the address space enormously and simplifies routing and autoconfiguration. Addresses can be public (globally routable) or private (reserved ranges like 10.0.0.0/8, used behind NAT).
- Uniquely identifies a device for routing packets
- Splits into network and host portions for hierarchy
- Public vs private ranges enable NAT and address conservation
- IPv6 solves IPv4 exhaustion with a vastly larger space
AI Mentor Explanation
An IP address is like the exact seat number printed on a spectator’s ticket — the stadium name gets you to the ground, but the seat number is what lets an usher deliver a message to that one specific person in a crowd of thousands. Two people can share a stadium but never the same seat number at the same time. Routers act like ushers, reading the seat number on each “packet” of popcorn orders to hand it to the right row and then the right seat.
Step-by-Step Explanation
Step 1
Assignment
A device gets an IP address statically or dynamically via DHCP when it joins a network.
Step 2
Structure
IPv4 (32-bit, dotted decimal) or IPv6 (128-bit, hex) splits into network and host portions.
Step 3
Public vs private
Public addresses are globally routable; private ranges are reused behind NAT.
Step 4
Routing
Routers read the destination IP on each packet to forward it hop by hop toward the target host.
What Interviewer Expects
- Clear definition: unique identifier used for routing
- IPv4 vs IPv6 structure and address length
- Public vs private address ranges and NAT
- How routers use the address to forward packets
Common Mistakes
- Confusing an IP address with a MAC address
- Thinking private IPs are globally unique
- Not knowing IPv4 addresses are 32-bit / IPv6 are 128-bit
- Forgetting that DHCP can change a device’s IP over time
Best Answer (HR Friendly)
“An IP address is like a device’s postal address on a network — a unique number that lets other devices and routers know exactly where to send data. Every device online, from your phone to a server, has one, and it is what makes it possible for information to reach the right destination out of billions of connected devices.”
Code Example
# Show this machine's IP addresses (Linux)
ip addr show
# Ping a host by IP to check reachability
ping -c 4 8.8.8.8
# Look up the public IP address this machine is seen as
curl -s https://api.ipify.org
# 203.0.113.42Follow-up Questions
- What is the difference between a public and a private IP address?
- How does NAT let many devices share one public IP?
- What is CIDR notation and how is it used?
- Why was IPv6 introduced over IPv4?
MCQ Practice
1. How many bits does a standard IPv4 address use?
IPv4 addresses are 32-bit, commonly written as four dotted decimal octets.
2. Which of these is a private IP address range?
192.168.0.0/16 is a reserved private address range used behind NAT.
3. What mechanism commonly assigns IP addresses automatically?
DHCP (Dynamic Host Configuration Protocol) automatically assigns IP addresses to devices.
Flash Cards
What is an IP address? — A unique numeric identifier assigned to a device for routing packets on a network.
IPv4 vs IPv6 size? — IPv4 is 32-bit (dotted decimal); IPv6 is 128-bit (hexadecimal).
Public vs private IP? — Public is globally routable; private (e.g. 10.0.0.0/8) is reused behind NAT.
How is an IP assigned? — Statically by an admin, or dynamically by a DHCP server.