IPv6
Also known as: internet protocol version 6
IPv6 is the most recent version of the Internet Protocol, using 128-bit addresses written in hexadecimal to provide a vastly larger address space than IPv4, along with built-in features like stateless address autoconfiguration.
IPv6 (Internet Protocol version 6) is the successor to IPv4, created because the internet was running out of IPv4's roughly 4.3 billion addresses. IPv6 addresses are 128 bits long — providing about 3.4 × 10³⁸ possible addresses — written as eight groups of four hexadecimal digits separated by colons, such as 2001:0db8:0000:0000:0000:0000:0000:0001.
Two abbreviation rules keep addresses readable: leading zeros within a group can be dropped, and one consecutive run of all-zero groups can be replaced with a double colon (::) — but only once per address. The example above shortens to 2001:db8::1. Instead of a subnet mask, IPv6 uses prefix length notation like /64, the standard size for a LAN segment.
IPv6 defines several address types. Global unicast addresses (currently 2000::/3) are publicly routable; link-local addresses (FE80::/10) are automatically assigned on every interface and used for on-link communication; unique local addresses (FC00::/7) are private; and multicast addresses (FF00::/8) replace broadcast, which no longer exists. Hosts can configure themselves without a DHCP server through stateless address autoconfiguration (SLAAC), building an address from the router-advertised prefix and an interface identifier. During the ongoing transition from IPv4, networks commonly run dual stack — both protocols simultaneously — or tunnel one protocol inside the other.
The CCNA exam tests IPv6 extensively: address compression and expansion, identifying address types by prefix, SLAAC and EUI-64 interface IDs, IPv6 static routing, and the absence of broadcast traffic are all fair game.
Key takeaways
- IPv6 uses 128-bit hexadecimal addresses, eliminating the address exhaustion problem of 32-bit IPv4.
- Addresses shorten by dropping leading zeros and collapsing one run of zero groups with :: (usable only once).
- Key address types: global unicast (2000::/3), link-local (FE80::/10), unique local (FC00::/7), and multicast (FF00::/8) — IPv6 has no broadcast.
- SLAAC lets hosts self-configure addresses from router advertisements without a DHCP server.
- The CCNA tests address abbreviation, address type identification, SLAAC, and IPv6 routing.