IPv4 vs IPv6 Differences
A detailed comparison of IPv4 and IPv6 across address space, headers, security, and features.
IPv4 vs IPv6 at a Glance
| Feature | IPv4 | IPv6 |
|---|---|---|
| Address length | 32 bits | 128 bits |
| Address count | ~4.3 billion | ~340 undecillion |
| Notation | Dotted decimal (192.168.1.1) |
Colon hex (2001:db8::1) |
| Header size | 20–60 bytes (variable) | 40 bytes (fixed) |
| Checksum | Yes (in header) | No (delegated to upper layers) |
| NAT | Widely used | Not needed |
| IPsec | Optional | Built-in |
| Auto-config | DHCP | SLAAC + DHCPv6 |
| Broadcast | Yes | No (multicast instead) |
Address Space
IPv4's 4.3 billion addresses were exhausted in 2011 (IANA) and continue to be depleted at regional levels. IPv6's address space is essentially unlimited for practical purposes — you could assign trillions of addresses to every human on Earth.
Simplified Header
IPv6 has a fixed 40-byte header compared to IPv4's variable-length header. IPv6 achieves this by:
- Removing the header checksum (upper layers handle this)
- Removing fragmentation fields (handled by source, not routers)
- Using extension headers for optional features
This fixed header allows routers to process IPv6 packets more efficiently.
No More NAT
IPv6's vast address space eliminates the need for NAT. Every device can have a globally unique address, enabling true end-to-end connectivity. This simplifies peer-to-peer applications, VoIP, and IoT deployments.
Built-in Security
IPv6 was designed with IPsec (IP Security) as a mandatory feature, providing authentication and encryption at the network layer. While IPsec can be used with IPv4, it's optional.
Auto-Configuration (SLAAC)
SLAAC (Stateless Address Autoconfiguration) allows IPv6 devices to configure their own addresses without a DHCP server:
- Device generates a link-local address (
fe80::...) - Device sends a Router Solicitation
- Router responds with network prefix
- Device combines prefix with its interface identifier
Multicast Instead of Broadcast
IPv6 replaces broadcast with multicast and anycast:
- Multicast (
ff02::1) — Sends to a group of interested devices - Anycast — Sends to the nearest member of a group
This reduces unnecessary traffic on the network.
Current Adoption
As of 2025, approximately 40-45% of internet traffic uses IPv6 globally, with some countries (India, Germany, USA) exceeding 50%. The transition is ongoing but slow — many networks still run dual-stack (both IPv4 and IPv6).