IPv6 address types

One device, several addresses

In IPv4 a laptop usually has one address per network card. IPv6 is different: the same interface normally carries several addresses at the same time, each with its own job. Three types matter first, and the first few hex digits tell you which one you're looking at. Think of them as three kinds of mail.

Global unicast: your full mailing address

A global unicast address is like your full mailing address: it's unique across the internet and routers carry it anywhere. Today these come from the block 2000::/3, so the first hex digit is a 2 or a 3. An example is 2001:db8::10 (the 2001:db8:: range is reserved for examples and documentation, so you won't see it on a real network).

Link-local: a note over the fence

A link-local address is like a note passed over the fence to your neighbor. It only works on your local link, the network segment your device is plugged into, and routers never forward it to another network. Link-local addresses come from fe80::/10, and in practice they start with fe80.

Every IPv6 interface creates one by itself, even with no router or DHCP server around. Devices use it to talk to their neighbors and to their router, for example to find out which network they're on.

Multicast: a group mailing list

A multicast address is like a group mailing list: the sender sends one packet, and every device that joined the group gets a copy. Devices that didn't join ignore it. Multicast addresses come from ff00::/8, so they start with ff. For example, ff02::1 means "every IPv6 device on this link".

IPv6 has no broadcast at all. Jobs that IPv4 did with broadcast are done with multicast instead, so only the devices that care get interrupted.

Try it yourself

Look at your own IPv6 addresses:

• Windows: open Command Prompt and run ipconfig. Look for "Link-local IPv6 Address" (starts with fe80) and, if your network has IPv6, "IPv6 Address" (often starts with 2).
• Mac or Linux: run ifconfig or ip -6 addr and find the lines starting with inet6.

Count how many addresses one interface has. You'll almost always find a fe80 address, even on networks without IPv6 internet.

Good to know

• Global unicast is currently allocated from 2000::/3, so the first hex digit is 2 or 3.
• Link-local is fe80::/10; multicast is ff00::/8 (RFC 4291).
• Every IPv6-enabled interface automatically has a link-local address.
• Left out for later: unique local (fc00::/7, like private IPv4), loopback ::1, and anycast.

For CCNA learners

This lines up with CCNA 200-301 exam topic 1.9, describe IPv6 address types: be able to name global unicast, link-local and multicast from their leading digits, and remember that IPv6 has no broadcast.

Answer to the comment question

Routers never forward link-local addresses (fe80::/10). A link-local address is only valid on the local link your device is plugged into, like a note passed over the fence, so a router won't pass it on to another network. Global unicast addresses are routed across the internet, and multicast can reach group members on other networks, depending on its scope.