SLAAC

/ˈsliː-æk/

n. “When your device gives itself an IPv6 address without asking permission.”

SLAAC, short for Stateless Address Auto-Configuration, is an IPv6 mechanism that allows devices to automatically configure their own IP addresses without requiring a DHCP server. As soon as a device connects to an IPv6-enabled network, it can generate a valid address and begin communicating almost immediately.

SLAAC works by combining two main pieces of information:

• Network Prefix: Advertised by routers using Router Advertisement (RA) messages.
• Interface Identifier: Generated by the device itself, often derived from the network interface or created randomly for privacy.

When a router sends an RA message, it tells devices which IPv6 prefix to use and whether SLAAC is permitted. The device then appends its own identifier to that prefix, forming a complete 128-bit IPv6 address.

A simplified example looks like this:

Router prefix: 2001:db8:abcd:0012::/64
Device identifier: ::a1b2:c3d4:e5f6

Resulting IPv6 address:
2001:db8:abcd:12:a1b2:c3d4:e5f6

Key characteristics of SLAAC include:

• Stateless: Routers do not track which addresses are assigned to which devices.
• No DHCP Required: Address assignment happens automatically without a central server.
• Fast Network Access: Devices can communicate as soon as they receive router advertisements.
• Privacy Extensions: Modern systems often generate temporary, randomized interface identifiers to reduce tracking.

Conceptually, SLAAC is like walking into a city where the street name is posted at the entrance, and every building is allowed to pick its own house number — no paperwork, no clerk, no waiting.

In essence, SLAAC is one of the features that makes IPv6 feel modern and lightweight, enabling large-scale, plug-and-play networking while reducing administrative overhead.