Stateless Auto-configuration
ICMPv6 Messages

Stateless auto-configuration uses the following ICMPv6 messages for its activities:

Before we discuss the principle of SLAAC, it is necessary to explain a Router Advertisement message.

Router Advertisement

The fundamental block of SLAAC is a Router Advertisement message. RA message is used for sending all necessary configuration parameters to nodes. Routers send out RA messages periodically, or in response to RS message.

Router Advertisement Message Format

Description of individual fields of RA message:

The significance of possible combination of M and O flags is shown in the following table.

The Combination of M and O Flags

M flag

O flag

Significance

1

-

DHCPv6 assigns all parameters

0

1

Combination of SLAAC (IPv6 address, prefix, routing) and DHCPv6 (other configuration parameters)

0

0

DHCPv6 is not available

Default Router Preference

Prf

Significance

01

High

00

Medium (default)

11

Low

10

Reserved (must not be sent)

Prefix Information Option Format

Description of individual fields of Prefix Information option: