IPv4 vs IPv6: Key Differences
10 min read•Published Sep 2, 2025
Understand the technical differences between IPv4 and IPv6, and why the internet is transitioning.
IPv4 vs IPv6 at a glance
IPv4 has powered the internet since the 1980s. It uses 32‑bit addresses like 203.0.113.5 and there aren’t many left. IPv6 fixes that with 128‑bit addresses like 2001:db8::1 and some helpful improvements for performance and security.
IPv4 (32‑bit)
- • Dotted decimal (e.g., 192.0.2.10)
- • ~4.3B addresses → scarcity and NAT
- • Mature, universal support
IPv6 (128‑bit)
- • Hexadecimal with colons (e.g., 2001:db8::1)
- • Vast address space → end‑to‑end addressing
- • Cleaner headers, better multicast, privacy options
Address formats and examples
IPv4
198.51.100.42
Four octets (0‑255) separated by dots.
IPv6
2001:0db8:0000:0000:0000:0000:0000:0001 → 2001:db8::1
Hex groups with shortcuts: drop leading zeros and compress one run of zeros with ::
New to IPs? Read the basics in What is an IP Address?
Key technical differences
Address space
IPv4: 32‑bit (~4.3B)
IPv6: 128‑bit (enormous)
Impact: No need for widespread NAT on IPv6
Headers
IPv4: Variable 20–60 bytes
IPv6: Fixed 40 bytes
Impact: Simpler, faster routing
Configuration
IPv4: Manual/DHCP
IPv6: SLAAC + DHCPv6
Impact: Easier host onboarding
Fragmentation
IPv4: Routers and hosts
IPv6: Source hosts only
Impact: Less router work
Multicast/Anycast
IPv4: Limited
IPv6: First‑class
Impact: Better group delivery and CDN routing
Security
IPv4: IPSec optional
IPv6: Designed with IPSec
Impact: Stronger end‑to‑end options
Security and performance
Security highlights
- IPSec support baked in
- Secure Neighbor Discovery (SEND)
- Privacy extensions for rotating addresses
Performance notes
- No router fragmentation
- Better multicast and anycast
- Mobile‑friendly design
Transition strategies
Dual‑stack: Run IPv4 and IPv6 side by side.
Tunneling: Encapsulate IPv6 over IPv4 (or the reverse) to cross gaps.
Translation: NAT64/DNS64 and similar when dual‑stack isn’t possible.
Adoption today
Adoption keeps climbing as ISPs, clouds, and mobile networks ship IPv6 by default. Many sites already serve content over both protocols. For most users, the transition is invisible—things just work.
What this means for you
- Users: Expect better reliability; some networks are faster on IPv6.
- Admins: Plan dual‑stack, monitoring, and staff training. Update firewalls.
- Developers: Validate longer addresses, test both paths, and store IPv6 safely.
Key takeaways
- IPv6 solves address exhaustion and simplifies routing.
- You’ll see fewer NAT workarounds and better end‑to‑end options.
- Run dual‑stack during migration; test both paths.