IPv6 Explained: Why It Exists and Why We Still Use IPv4 Too

Open a command promptIn plain words: A window where you type instructions instead of clicking. The shortcut name is cmd.Technical: Windows’ text-mode shell (cmd.exe). PowerShell is a newer one. On a Mac the equivalent is Terminal.Click for the full glossary entry and type:

> ipconfig

Find the section for your Wi-Fi or Ethernet connection. Besides the IPv4 AddressIn plain words: A device’s street address on a network: four numbers separated by dots, like 192.168.1.37.Technical: A 32-bit number (IPv4), written as four octets. It combines which network the device is on and which device it is on that network.Click for the full glossary entry you already know, you will probably see lines like these (this is an example; yours will differ):

   IPv6 Address. . . . . . . . . . . : 2001:db8:1234:5678:a1b2:c3d4:e5f6:7890
   Temporary IPv6 Address. . . . . . : 2001:db8:1234:5678:1111:2222:3333:4444
   Link-local IPv6 Address . . . . . : fe80::a1b2:c3d4:e5f6:7890%12
   IPv4 Address. . . . . . . . . . . : 192.168.1.37

• Link-local (starts with fe80) — every IPv6In plain words: The newer kind of internet address, long enough that we will never run out. It looks like 2001:db8::1, with letters and colons. Windows has it switched on already.Technical: 128-bit addresses written as eight groups of hex, defined in RFC 8200 and RFC 4291. Devices usually run IPv4 and IPv6 side by side (dual-stack).Click for the full glossary entry computer gives itself one. It only works on your own local network and never crosses the routerIn plain words: The box that connects your home to the internet and passes data between networks.Technical: Forwards packets between networks. At home it is usually also the Wi-Fi access point and the DHCP server.Click for the full glossary entry. You will see this one even when your internet provider does not offer IPv6.
• IPv6 Address and Temporary IPv6 Address (start with 2 or 3) — a real, internet-usable address. You only see these if your provider offers IPv6. The “temporary” one is changed regularly so websites cannot easily track your device.

If you only see the fe80 line, your connection is not giving you IPv6 on the internet. That is common and perfectly normal.

Why this matters. Windows has IPv6 on by default and prefers it when it works. So when something behaves differently on one network than another, the answer is often “one of them has IPv6 and the other does not.”

An IPv4In plain words: The original kind of internet address: four numbers with dots, like 192.168.1.37. There are only about 4.3 billion of them, and they ran out.Technical: 32-bit addresses (about 4.3 billion). The free pools of the regional registries ran out between 2011 and 2015, which is why NAT is everywhere.Click for the full glossary entry address is 32 bitsIn plain words: A bit is one on-or-off switch. Eight of them make a byte.Technical: The smallest unit of data: 0 or 1. An IPv4 address is 32 bits, grouped as four 8-bit octets.Click for the full glossary entry, which gives 2³² = 4,294,967,296 addresses, about 4.3 billion. That sounded like plenty in the 1980s. It was not enough for a world with billions of phones, laptops, TVs and sensors.

• The top-level pool of IPv4 addresses was handed out by 2011, and the regional registries ran out one after another. North America’s (ARIN) ran out in 2015.
• An IPv6In plain words: The newer kind of internet address, long enough that we will never run out. It looks like 2001:db8::1, with letters and colons. Windows has it switched on already.Technical: 128-bit addresses written as eight groups of hex, defined in RFC 8200 and RFC 4291. Devices usually run IPv4 and IPv6 side by side (dual-stack).Click for the full glossary entry address is 128 bits, which gives 2¹²⁸ = about 3.4 × 10³⁸ addresses. That is not just “a lot more.” Every grain of sand on Earth could have billions of addresses.

IPv6 is defined in RFC 8200 (the protocol) and RFC 4291 (how addresses are laid out).

Why this matters. Almost everything awkward about modern home networks (private addressesIn plain words: An address used inside your home or office only, like an apartment number: many buildings reuse the same ones.Technical: Reserved ranges: 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. Not routable across the internet.Click for the full glossary entry, NATIn plain words: What your router does to let every device in the house share one internet address, like a receptionist forwarding calls to the right desk.Technical: The router rewrites private source addresses to its public address and remembers each conversation so replies return to the right device.Click for the full glossary entry, port forwarding) exists because IPv4 ran out.

An IPv6In plain words: The newer kind of internet address, long enough that we will never run out. It looks like 2001:db8::1, with letters and colons. Windows has it switched on already.Technical: 128-bit addresses written as eight groups of hex, defined in RFC 8200 and RFC 4291. Devices usually run IPv4 and IPv6 side by side (dual-stack).Click for the full glossary entry address is eight groups of four hexadecimal characters (0 to 9 and a to f), separated by colons. The full version is long, so there are two shortening rules:

  Full:       2001:0db8:0000:0000:0000:0000:0000:0001
  Rule 1:     drop leading zeros in each group  ->  2001:db8:0:0:0:0:0:1
  Rule 2:     replace ONE run of all-zero groups with ::  ->  2001:db8::1

• You can use :: only once in an address, otherwise it would be ambiguous.
• The first half is usually the network and the second half is the device. The normal subnetIn plain words: A smaller neighbourhood carved out of a bigger network.Technical: A range of addresses sharing the same network prefix. Subnetting divides a network to organise traffic and control who can talk to whom.Click for the full glossary entry size is /64, which is 64 bitsIn plain words: A bit is one on-or-off switch. Eight of them make a byte.Technical: The smallest unit of data: 0 or 1. An IPv4 address is 32 bits, grouped as four 8-bit octets.Click for the full glossary entry for the network and 64 for the device.
• ::1 means “this computer” (like 127.0.0.1 in IPv4In plain words: The original kind of internet address: four numbers with dots, like 192.168.1.37. There are only about 4.3 billion of them, and they ran out.Technical: 32-bit addresses (about 4.3 billion). The free pools of the regional registries ran out between 2011 and 2015, which is why NAT is everywhere.Click for the full glossary entry).
• Addresses starting with 2 or 3 are the global, internet addresses.
• Addresses starting with fe80 are link-local, as in step 1.
• Addresses starting with fc or fd are the privateIn plain words: An address used inside your home or office only, like an apartment number: many buildings reuse the same ones.Technical: Reserved ranges: 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. Not routable across the internet.Click for the full glossary entry ones (called unique local addresses).
• 2001:db8 is reserved for examples and documentation, which is why you see it in lessons.
• There is no broadcast address in IPv6, and no dotted subnet masks. Everything uses the slash.

Why this matters. The same idea as subnetting: part of the address is the network and part is the device. IPv6 just has far more room, so the usual home network gets a /64 with 2⁶⁴ addresses.

IPv6In plain words: The newer kind of internet address, long enough that we will never run out. It looks like 2001:db8::1, with letters and colons. Windows has it switched on already.Technical: 128-bit addresses written as eight groups of hex, defined in RFC 8200 and RFC 4291. Devices usually run IPv4 and IPv6 side by side (dual-stack).Click for the full glossary entry gives devices two ways to get an address, and the first needs no server at all.

• SLAAC (stateless address autoconfiguration, RFC 4862) — your routerIn plain words: The box that connects your home to the internet and passes data between networks.Technical: Forwards packets between networks. At home it is usually also the Wi-Fi access point and the DHCP server.Click for the full glossary entry announces “this is the network prefix” in a message called a router advertisement, and each device builds its own address from that prefix plus a number it picks. No DHCPIn plain words: The front desk of your network. When a phone or laptop joins, DHCP hands it an address, like a hotel handing you a room key, so nobody types it in by hand.Technical: Dynamic Host Configuration Protocol. A service, normally on your router, that leases each device an IP address, subnet mask, gateway and DNS server automatically.Click for the full glossary entry needed.
• DHCPv6 (RFC 8415) — the IPv6 version of the DHCP you learned about, used when a network wants to control which addresses are handed out, or to hand out other settings.

Windows normally makes the device half of the address random, and changes the temporary address regularly, so your address does not reveal your hardware (RFC 8981).

Why this matters. In IPv6 the old ARP system is replaced by a similar one that runs over ICMPv6, and a rogue device sending fake router advertisements can redirect other devices’ traffic.

The defender’s move. Managed switchesIn plain words: A little extra word after a command that changes how it works, like setting the oven to “fan.”Technical: An argument starting with - or / that modifies a command, for example the -d in tracert -d. Each command has its own list.Click for the full glossary entry can block router advertisements from ports that should not send them (“RA guard”). It is a Security+ topic.

Open test-ipv6.com in your browser and read the result. It tells you whether your computer can reach the internet over IPv6In plain words: The newer kind of internet address, long enough that we will never run out. It looks like 2001:db8::1, with letters and colons. Windows has it switched on already.Technical: 128-bit addresses written as eight groups of hex, defined in RFC 8200 and RFC 4291. Devices usually run IPv4 and IPv6 side by side (dual-stack).Click for the full glossary entry, over IPv4In plain words: The original kind of internet address: four numbers with dots, like 192.168.1.37. There are only about 4.3 billion of them, and they ran out.Technical: 32-bit addresses (about 4.3 billion). The free pools of the regional registries ran out between 2011 and 2015, which is why NAT is everywhere.Click for the full glossary entry, or both.

In the command promptIn plain words: A window where you type instructions instead of clicking. The shortcut name is cmd.Technical: Windows’ text-mode shell (cmd.exe). PowerShell is a newer one. On a Mac the equivalent is Terminal.Click for the full glossary entry, try:

> ping ::1
> ping -6 example.com
> nslookup -type=AAAA example.com

• ping ::1 should always work. It tests your own IPv6 software.
• ping -6 example.com forces IPv6. If your provider does not give you IPv6, this fails, which is fine.
• nslookup -type=AAAA example.com asks DNSIn plain words: The internet’s phone book. You type an easy name like stashgrid.ai, and DNS looks up the number address that computers really use, the way a street address tells the mail carrier where to go.Technical: Domain Name System. A worldwide set of servers that turns names into IP addresses. Your device asks a DNS server (usually your router or your provider) every time you visit a site.Click for the full glossary entry for the IPv6 address of the site (an AAAA recordIn plain words: The different kinds of answer DNS can give: an address, a mail server, who is in charge, or a note.Technical: A maps a name to an IPv4 address, AAAA to an IPv6 address, CNAME to another name, MX to mail servers, NS to the zone’s name servers, TXT to free text such as SPF policies.Click for the full glossary entry). The site can have one even if you cannot use it.

Why this matters. A site can have an IPv6 address while your connection cannot reach it, or the other way round. Testing each separately is how you find which half is broken.

IPv6In plain words: The newer kind of internet address, long enough that we will never run out. It looks like 2001:db8::1, with letters and colons. Windows has it switched on already.Technical: 128-bit addresses written as eight groups of hex, defined in RFC 8200 and RFC 4291. Devices usually run IPv4 and IPv6 side by side (dual-stack).Click for the full glossary entry was standardised in the 1990s. In April 2026, Google reported for the first time that half of the connections to it use IPv6. APNIC, which measures differently and weights by number of users, puts the world at roughly 42%. Both numbers show the same thing: well over a decade of growth, and not finished.

The honest reasons it is slow:

• NATIn plain words: What your router does to let every device in the house share one internet address, like a receptionist forwarding calls to the right desk.Technical: The router rewrites private source addresses to its public address and remembers each conversation so replies return to the right device.Click for the full glossary entry bought time. Sharing one IPv4In plain words: The original kind of internet address: four numbers with dots, like 192.168.1.37. There are only about 4.3 billion of them, and they ran out.Technical: 32-bit addresses (about 4.3 billion). The free pools of the regional registries ran out between 2011 and 2015, which is why NAT is everywhere.Click for the full glossary entry address between a whole house removed the urgency.
• It is not backward compatible. An IPv6-only device cannot talk to an IPv4-only server directly, so networks run both at once (called dual-stackIn plain words: Using the old and new kinds of address at the same time, like a shop with a front door and a new side door.Technical: A host or network running IPv4 and IPv6 together. It is how the transition is done, because IPv6 is not backward compatible with IPv4.Click for the full glossary entry), and that costs more.
• Nobody wins by going first. A website gains little from IPv6 until users have it, and users gain little until websites offer it.
• Old equipment and software. Routers, cameras, printers and company systems that only know IPv4 are expensive to replace.
• It is uneven. Some countries and mobile networks lead, because new networks find IPv6 cheaper to build.
• Nobody can switchIn plain words: A little extra word after a command that changes how it works, like setting the oven to “fan.”Technical: An argument starting with - or / that modifies a command, for example the -d in tracert -d. Each command has its own list.Click for the full glossary entry it off for everyone. There is no date for turning IPv4 off, so expect both for many years.

Sources and live numbers: APNIC: Google hits 50% IPv6 and Google’s IPv6 statistics.

Why this matters. The practical lesson: you will keep seeing both kinds of address for the rest of your career. Learn both.

Forum posts sometimes say to turn IPv6In plain words: The newer kind of internet address, long enough that we will never run out. It looks like 2001:db8::1, with letters and colons. Windows has it switched on already.Technical: 128-bit addresses written as eight groups of hex, defined in RFC 8200 and RFC 4291. Devices usually run IPv4 and IPv6 side by side (dual-stack).Click for the full glossary entry off to fix a slow connection. Microsoft’s guidance is to leave it on, because parts of Windows rely on it, and turning it off can cause hard-to-find problems.

• If IPv6 seems to be the problem, test with ping -6 and the website above first. Often the real culprit is the routerIn plain words: The box that connects your home to the internet and passes data between networks.Technical: Forwards packets between networks. At home it is usually also the Wi-Fi access point and the DHCP server.Click for the full glossary entry or the internet provider.
• IPv6 is not automatically safer or less safe. Because each device can have an internet-reachable address, you need a firewall that covers IPv6. Home routers normally block unsolicited incoming IPv6 by default, but check yours.
• NATIn plain words: What your router does to let every device in the house share one internet address, like a receptionist forwarding calls to the right desk.Technical: The router rewrites private source addresses to its public address and remembers each conversation so replies return to the right device.Click for the full glossary entry is not a firewall. IPv4In plain words: The original kind of internet address: four numbers with dots, like 192.168.1.37. There are only about 4.3 billion of them, and they ran out.Technical: 32-bit addresses (about 4.3 billion). The free pools of the regional registries ran out between 2011 and 2015, which is why NAT is everywhere.Click for the full glossary entry homes were protected by a side effect of NAT. IPv6 homes are protected by the firewall rules, so make sure there are some.
• The defender’s view. If you only watch and log IPv4 traffic, you can miss what happens over IPv6. Security tools need to see both.

Disabling IPv6 to fix a problem is the networking equivalent of removing the smoke alarm because it keeps beeping. — Nyx