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How does IPv4 differ from IPv6?

Networking & InternetMiddle~2 min read
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IPv4 and IPv6 are two versions of the IP protocol that solve the same task (addressing and delivering packets), but differ greatly in capabilities and structure.

Short version: IPv6 is a modern, expanded version of IPv4, created because of address exhaustion and IPv4's technical limitations.

Main differences between IPv4 and IPv6

1. Address space size

The most important difference.

  • IPv4
    • address length: 32 bits
    • ~4.3 billion addresses
    • addresses have practically run out
  • IPv6
    • address length: 128 bits
    • a huge number of addresses
    • no address shortage

2. Address notation

  • IPv4

    192.168.1.10
    • decimal notation
    • 4 numbers of 8 bits each

  • IPv6

    2001:db8::1
    • hexadecimal notation
    • 8 groups of 16 bits each
    • shortening is allowed (::)

3. Broadcast and multicast

  • IPv4
    • has broadcast
    • has multicast
  • IPv6
    • no broadcast
    • only multicast and unicast are used

This reduces unnecessary traffic on the network.

4. NAT

  • IPv4
    • NAT is widely used
    • one public IP for many devices
  • IPv6
    • NAT is not needed
    • each device can have a public address

5. Packet header

  • IPv4
    • variable header length
    • more complex processing
  • IPv6
    • fixed header
    • simplified routing
    • extra fields moved into extensions

6. Autoconfiguration

  • IPv4
    • usually needs DHCP
    • or manual configuration
  • IPv6
    • built-in autoconfiguration (SLAAC)
    • can work without DHCP

7. Security

  • IPv4
    • IPsec is not mandatory
  • IPv6
    • IPsec is built into the standard
    • security is designed in from the start

Short table of differences

CharacteristicIPv4IPv6
Address length32 bits128 bits
FormatDecimalHexadecimal
Number of addressesLimitedHuge
BroadcastYesNo
NATWidely usedNot required
HeaderVariableFixed
AutoconfigurationLimitedBuilt-in

What is important for an interview

  • IPv6 is not backward compatible with IPv4
  • for interoperability, these are used:
    • dual stack
    • tunneling
    • translation

In short, for an interview

IPv6 differs from IPv4 in its larger address space, lack of broadcast, simplified header, built-in autoconfiguration, and reduced need for NAT, which makes it more scalable and modern.

Short Answer

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