IPv4 vs IPv6

Quick reference

	IPV4	IPV6
Address size	32 bits, 4 octets	128 bits, 16 octets
Written as	203.0.113.10	2001:db8::10
DNS record	A	AAAA
Configuration	DHCP or manual	SLAAC, DHCPv6 optional
NAT	Common, address shortage	Rare, no shortage
Discovery	ARP and broadcast	NDP and multicast

IPV4 (32-bit dotted quad): Four bytes, four decimal octets, and most of the internet.

$dig example.com A +short

IPV6 (128-bit hex groups): Sixteen bytes, eight hex groups, and :: for a run of zeros.

$dig example.com AAAA +short

IPv4 → everywhere, and out of addresses.
IPv6 → the same internet, with room.

Explained

Size and notation

IPv4 is 32 bits, written as four decimal octets such as 203.0.113.10. IPv6 is 128 bits, written as eight groups of four hex digits, with :: allowed once for a run of zeros, as in 2001:db8::10.

DNS and configuration

An A record holds an IPv4 address and an AAAA record holds an IPv6 one. IPv4 hosts get an address from DHCP or a static file; IPv6 hosts usually build one from a router advertisement with SLAAC, and DHCPv6 is optional.

NAT and discovery

IPv4 often sits behind NAT because the address space ran out, so many hosts share one public address. IPv6 has enough addresses that NAT is rare, though NPTv6 exists for translation. IPv4 finds neighbours with ARP and broadcast; IPv6 uses Neighbour Discovery over multicast, with no broadcast at all. The two run side by side on one host, and a client with a working IPv6 path will usually try it first.

The honest caveat: dual stack is the normal deployment, not a migration deadline, and an IPv6 path is not automatically faster; it is a different path that has to be measured.

The lesson: choose the record by what the client can reach, not by what the RFC prefers.

Two protocols, one address space.