Nexnet AcademyV1 · alpha
Sign in
← CourseIPv6 Fundamentals~5 min read

IPv6: the address space that doesn't run out

Why IPv6 exists

IPv4 has about 4.3 billion addresses - we ran out. IPv6 uses 128-bit addresses (written in hexadecimal), giving a practically unlimited supply. It also drops broadcasts in favour of multicast and neighbour discovery, and simplifies the header.

Reading and shortening an address

An IPv6 address is eight groups of four hex digits separated by colons, e.g. 2001:0db8:0000:0000:0000:ff00:0042:8329. Two rules shorten it: drop leading zeros in each group, and replace ONE run of all-zero groups with '::'. That example becomes 2001:db8::ff00:42:8329. You may use '::' only once, because otherwise the length would be ambiguous.

Address types

Global unicast (starts 2000::/3) is internet-routable, like a public IPv4. Link-local (fe80::/10) is auto-configured on every interface and used only on the local link - a bit like APIPA. Unique local (fc00::/7) is the private-use range. Multicast (ff00::/8) replaces broadcast. Loopback is ::1.

Getting an address

Hosts often self-assign using SLAAC, learning the network prefix from a router advertisement and generating the interface ID themselves - no DHCP server required. DHCPv6 is still available when central control is needed. Dual-stack means running IPv4 and IPv6 side by side during the transition.

Concept cards

IPv6 address

A 128-bit address written as eight groups of hex digits, shortenable with '::'.

A phone-number system so large every grain of sand could have its own.

Link-local (fe80::/10)

An address every interface auto-configures, valid only on the local link.

A nickname that only makes sense inside one room.

SLAAC

Stateless address autoconfiguration - the host builds its own address from the router's advertised prefix.

Being told the street name and picking your own house number.

Now try it
M06-01IPv6 Compressor
Start the mission →