What is SLAAC (stateless address autoconfiguration)?

An IPv6 mechanism in which a host learns the network prefix (normally a /64) from the router advertisements (RAs) sent by routers and combines it with an interface ID it creates itself to configure an address automatically. The interface ID is either in the EUI-64 format derived from the MAC address or based on a random value to prevent tracking. Before using the address, the host checks with duplicate address detection (DAD) that no other device has it.

Japanese name: SLAAC(ステートレスアドレス自動設定)

SLAAC (stateless address autoconfiguration) appears in 2 practice questions across 1 topic, including Network Design and Operations.

Field: Network Design and Operations

Try it: questions about SLAAC (stateless address autoconfiguration)

In IPv6 SLAAC (stateless address autoconfiguration), how does a host create a global unicast address?

AIt queries a DHCPv6 server and leases a 128-bit address managed by the server for a set period
BIt combines the /64 prefix in the router advertisement (RA) sent by a router with an interface ID (the lower 64 bits) it creates itself, and uses the address after checking that no other device has the same address
CIt puts its own IPv4 address as it is into the lower 32 bits and fills the upper bits with a value starting with fe80

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Answer: B. It combines the /64 prefix in the router advertisement (RA) sent by a router with an interface ID (the lower 64 bits) it creates itself, and uses the address after checking that no other device has the same address

With SLAAC, a host learns the prefix of its link (normally a /64) from the router advertisements (RAs) that routers send periodically or on request. It combines this with an interface ID, either in the EUI-64 format derived from its MAC address or based on a random value, to form an address. Before using it, the host uses Neighbor Discovery to check that no other device is using the same address (duplicate address detection, DAD). The link-local address of the router that sent the RA becomes the default gateway, and because no server manages the address assignments, it is called "stateless." DNS server addresses are provided by an RA option or by stateless DHCPv6.

An interface with MAC address 00-1A-2B-3C-4D-5E creates an address with SLAAC from the prefix 2001:db8:1:1::/64 and an interface ID in the EUI-64 format. Which address results?

A2001:db8:1:1:21a:2bff:fe3c:4d5e
B2001:db8:1:1:1a:2bff:fe3c:4d5e
C2001:db8:1:1:21a:2bfe:ff3c:4d5e

Show answer and explanation

Answer: A. 2001:db8:1:1:21a:2bff:fe3c:4d5e

In the EUI-64 format, the 48-bit MAC address is split into its upper 24 bits and lower 24 bits, and FF-FE is inserted between them to make 64 bits. Inserting it between 00-1A-2B and 3C-4D-5E gives 00-1A-2B-FF-FE-3C-4D-5E. In addition, the second-lowest bit of the first byte (the U/L bit) is inverted, so 00 becomes 02, giving 02-1A-2B-FF-FE-3C-4D-5E. Grouping this into 16-bit pieces and dropping leading zeros in each gives 21a:2bff:fe3c:4d5e, and with the prefix the address is 2001:db8:1:1:21a:2bff:fe3c:4d5e. Because an address that reveals the MAC address makes the host easier to track, most current operating systems use interface IDs based on random values.

SLAAC (stateless address autoconfiguration) in the explanations

With SLAAC, a host learns the prefix of its link (normally a /64) from the router advertisements (RAs) that routers send periodically or on request.
In IPv6 SLAAC (stateless address autoconfiguration), how do…