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Commonly confused · Networking Fundamentals

IPv4 vs IPv6: What's the Difference?

IPv4 uses 32-bit addresses written in dotted decimal and relies on NAT to stretch its limited space. IPv6 uses 128-bit hexadecimal addresses, eliminates broadcasts, and supports stateless address autoconfiguration.

IPv4IPv6
Address length32 bits (about 4.3 billion addresses)128 bits (about 3.4 x 10^38 addresses)
NotationDotted decimal, e.g. 192.168.1.10Hexadecimal, colon-separated, e.g. 2001:db8::1
BroadcastYesNo; uses multicast and anycast instead
Address resolutionARPNeighbor Discovery Protocol (ICMPv6)
AutoconfigurationDHCP or manual; APIPA fallbackSLAAC, DHCPv6, or manual
HeaderVariable length (20-60 bytes), includes checksumFixed 40 bytes, no header checksum; extension headers
Loopback127.0.0.1::1
Remember it

IPv6 is four times longer in bits, with no broadcasts and no ARP.

Exam tip

Expect address-shortening questions (dropping leading zeros, using :: once) and questions on IPv6 address types such as link-local (FE80::/10) and global unicast (2000::/3). Remember IPv6 replaces ARP with NDP.

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