On receipt of a valid Router Advertisement (as
described in RFC 2461 p.38), a host copies the value of the advertisement's M bit
into ManagedFlag. If the value of ManagedFlag changes from FALSE to
TRUE, and the host is not already running the stateful address
autoconfiguration protocol, the host should invoke the stateful
address autoconfiguration protocol, requesting both address
information and other information. If the value of the
ManagedFlag
changes from TRUE to FALSE, the host should continue running the
stateful address autoconfiguration.
If the value of the flag stays unchanged, no special action takes place.
The advertisement of the O flag field is processed very similar. A host copies the value of the O flag into OtherConfigFlag. If the value of OtherConfigFlag changes from FALSE to TRUE, the host should invoke the stateful autoconfiguration protocol, requesting information (excluding addresses if ManagedFlag is set to FALSE). If the value of the OtherConfigFlag changes from TRUE to FALSE, the host should continue running the stateful address autoconfiguration protocol. If the value of the flag stays unchanged, no special action takes place.
In particular, a host MUST NOT reinvoke stateful configuration if it is already participating in the stateful protocol as a result of an earlier advertisement.
For each Prefix-Information option in the Router Advertisement:
a) If the Autonomous flag is not set, silently ignore the Prefix Information option.
b) If the prefix is the link-local prefix, silently ignore the Prefix Information option.
c) If the preferred lifetime is greater than the valid
lifetime,
silently ignore the Prefix Information
option.
A node MAY wish to
log a system management error in this case.
d) If the prefix advertised does not match the prefix of an address already in the list, and the Valid Lifetime is not 0, form an address (and add it to the list) by combining the advertised prefix with the link's interface identifier as follows:
If the sum of the prefix length and
interface identifier length
does not equal 128 bits, the Prefix
Information option MUST be
ignored. An implementation MAY wish
to log a system management
error in this case.
It is the responsibility of the system administrator to insure that the lengths
of prefixes contained in Router Advertisements are consistent with the length of
interface identifiers for that link type.
If an address is formed successfully, the host adds it to the list of addresses assigned to the interface, initializing its preferred and valid lifetime values from the Prefix Information option.
e) If the advertised prefix matches the prefix of an autoconfigured address in the list of addresses associated with the interface, the specific action to perform depends on the Valid Lifetime in the received advertisement and the Lifetime associated with the previously autoconfigured address (we'll call it Stored Lifetime):
1) If the received Lifetime is greater than 2 hours or greater than StoredLifetime, update the stored Lifetime of the corresponding address.
2) If the StoredLifetime is less than or equal to 2 hours and the received Lifetime is less than or equal to Stored Lifetime, ignore the prefix, unless the Router Advertisement, from which this Prefix Information option was obtained, has been authenticated. If the Router Advertisment was authenticated, the Stored Lifetime should be set to the Lifetime in the received option.
The following diagram help understanding the above:
3) Otherwise, reset the stored Lifetime in the corresponding address to two hours.
