IPv4 vs IPv6: Key Differences, Addressing and How They Work Together

Nothing connects to the internet without an address, and today those addresses come in two generations of the same protocol. The older one, IPv4, packs an address into 32 bits shown as four numbers joined by dots, such as 192.0.2.10; that caps the supply at roughly 4.3 billion. The newer one, IPv6, stretches the address to 128 bits shown in hex groups, such as 2001:db8::10, a pool so vast that each person on Earth could own trillions of public addresses.

On the wire the two generations do not understand each other: a host limited to IPv4 cannot swap packets with a host limited to IPv6. So the internet carries both in parallel and will go on doing so for a long time. This guide contrasts their notation, headers, setup and security, explains the coexistence tricks and shows why the IP generation matters once proxies enter the picture.

IPv4 at a Glance

Thirty-two bits are divided into four octets, each printed as a value between 0 and 255: 198.51.100.42. A slash with a number, say /24, tells how many leading bits identify the network. Some blocks are set aside for private use, namely 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16, and routers on the public internet never forward them.

RFC 791 fixed the format back in 1981, when smartphones and smart bulbs belonged to science fiction. The 4,294,967,296 possible values proved far too few. IANA gave away its final free blocks in February 2011, regional registries emptied their stocks over the following years, and RIPE NCC, which serves Europe, hit zero in November 2019. Ever since, public IPv4 space has changed hands through purchases and leases, like any commodity in short supply.

IPv6 at a Glance

An IPv6 address consists of 128 bits arranged as eight colon-separated groups of four hex digits:

2001:0db8:0000:0000:0000:0000:0000:0010

In practice people write it far shorter. You may omit the zeros that open a group, and you may replace one block of consecutive zero groups with ::. Our sample thus becomes 2001:db8::10. Only one :: is permitted per address, because two of them would make it impossible to count the hidden groups.

In total there are about 3.4 × 10^38 values. Home subscribers often receive an entire /56 or even a /48 block, while every LAN inside it takes a /64, a single slice equal to the whole IPv4 space squared. The first formal description, RFC 1883, dates from 1995, and the version engineers consult today is RFC 8200, published in 2017.

What Changes Besides Address Size

Headers and Packet Processing

An IPv4 header spans 20 to 60 bytes and includes a checksum that each router has to recalculate. IPv6 settles on a constant 40 bytes with no checksum, pushing optional features into extension headers that transit routers mostly ignore. Packet size works differently as well. An IPv6 router never cuts a packet into pieces; the sending host probes the path MTU and sizes packets itself, and each IPv6 link is required to carry at least 1280 bytes in one piece.

NAT and Direct Reachability

Scarcity forced IPv4 networks to hide whole households and offices behind one public address via NAT, and mobile carriers stack a second translation layer, carrier-grade NAT, on top. It keeps things running, yet it breaks direct device-to-device links, complicates peer-to-peer software and lets one public IP stand for hundreds of subscribers. IPv6 makes translation unnecessary: each device may hold a globally routable address, and a firewall rather than NAT decides which inbound packets are welcome.

Setup and the Local Segment

An IPv4 host normally gets its settings via DHCP and locates neighbours with ARP broadcasts. IPv6 swaps broadcasts for multicast and ARP for Neighbor Discovery, and introduces stateless autoconfiguration, SLAAC, where a host learns the prefix from router advertisements and assembles its own address. DHCPv6 remains an option for administrators who want central control.

Security and Privacy

A persistent claim credits IPv6 with stronger security on account of bundled IPsec. The first IPv6 specifications told vendors to include IPsec code in every stack, yet whether to switch it on was always left to the administrator, and the requirement has since been relaxed to a recommendation, putting both generations on equal footing. The meaningful differences are elsewhere. Without NAT, a machine is reachable from outside unless a firewall drops unsolicited traffic, so IPv6 rules are mandatory, not optional. To keep sites from following a device by a fixed address, operating systems pick short-lived temporary addresses defined by the privacy extensions in RFC 8981.

Speed

Neither generation wins by design. IPv6 skips translation and uses a leaner header, and some ISPs route it more efficiently; others tunnel it and add delay. What you actually experience depends on your provider's paths. Online games bring their own trade-offs, which we examine in IPv4 vs IPv6 for gaming.

IPv4 and IPv6 Side by Side

How the Two Generations Coexist

• Dual stack. A computer or network runs the two protocols at once. When a domain publishes an A record for IPv4 and an AAAA record for IPv6, the client races the two and keeps whichever answers first, an algorithm called Happy Eyeballs (RFC 8305).
• Tunnelling. IPv6 packets ride inside IPv4 across stretches that lack native support, as in 6in4. Self-configuring relics like 6to4 and Teredo survive mostly in old documentation.
• Translation. When a phone holds only an IPv6 address and the website holds only an IPv4 one, a NAT64 gateway plus a DNS64 resolver rewrite the conversation between them, and mobile operators frequently add 464XLAT so that legacy IPv4 apps still function on handsets that get nothing but IPv6.

Google's published figures show roughly half of its users arriving over IPv6, with huge gaps between countries and carriers. Everything else still leans on IPv4, which is why the old protocol is in no danger of disappearing.

Finding Your Own Addresses

• Windows: in a terminal, ipconfig lists entries labelled "IPv4 Address" and "IPv6 Address".
• macOS and Linux: ifconfig or ip addr prints inet lines for the old protocol and inet6 lines for the new one.
• Public side: an IP test site shows your outward-facing addresses; better ones display both generations and confirm whether IPv6 works all the way through.

Ignore entries starting with fe80:: they serve only your own cable or Wi-Fi segment. Addresses reachable from the internet usually open with the digit 2 or 3.

Why the IP Generation Matters for Proxies

The moment traffic goes through a proxy, the version starts to count:

• Coverage. A site without an AAAA entry in DNS is invisible to an IPv6 exit. Large platforms do, but plenty of shops, forums and regional services remain IPv4-only, and an IPv6-only proxy simply cannot open them.
• Reputation. Anti-abuse systems tend to throttle and ban IPv6 by an entire /64 or /48 rather than by one address, so thousands of seemingly distinct IPv6 exits from a single prefix may be treated as one visitor.
• Cost and availability. IPv6 space is abundant and cheap; IPv4 space is scarce and priced accordingly. For scraping, ad verification and account work, IPv4 remains the dependable default.
• Leaks. When a proxy forwards IPv4 while your device also holds IPv6, some programs open IPv6 connections directly and reveal where you really are. Disable IPv6 inside such an app or make sure your client tunnels both generations.

Our guide to IPv4 proxies covers the older generation as a proxy product. Sites with tight checks accept residential proxies built on real home connections most readily, whereas datacenter proxies offer more speed per dollar on tolerant targets. Once configured, run the server through our proxy checker to see the exit address and which protocol it uses.

Which One to Use

On an everyday home or office network, leave dual stack on: IPv6 serves whatever supports it and IPv4 covers the rest. When launching a public service, publish both A and AAAA records from day one. For proxy work, IPv4 is the starting point; IPv6 earns a place once you have confirmed that all your targets answer over it and the job truly calls for a gigantic pool.