I read through RFC 2462 to find out the requirements level for host use of
the 'O' flag field ("other stateful configuration") in RAs. The only text
I found concerning the 'O' flag is"
(section 4, Protocol Overview)
Solicitations to the all-routers multicast group. Router
Advertisements contain two flags indicating what type of stateful
autoconfiguration (if any) should be performed. A "managed address
configuration" flag indicates whether hosts should use stateful
autoconfiguration to obtain addresses. An "other stateful
configuration" flag indicates whether hosts should use stateful
autoconfiguration to obtain additional information (excluding
addresses).
(section 5.2, Autoconfiguration-Related Variables)
OtherConfigFlag Copied from the O flag field (i.e., the "other
stateful configuration" flag) of the most
recently received Router Advertisement message.
The flag indicates whether or not information
other than addresses is to be obtained using the
stateful autoconfiguration mechanism. It starts
out in a FALSE state.
In addition, when the value of the ManagedFlag is
TRUE, the value of OtherConfigFlag is implicitly
TRUE as well. It is not a valid configuration for
a host to use stateful address autoconfiguration
to request addresses only, without also accepting
other configuration
information.
(section 5.5.3, Router Advertisement Processing)
An advertisement's O flag field is processed in an analogous manner.
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, i.e., the change in the value of OtherConfigFlag has no
effect. 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.
So, RFC 2462 only uses RFC 2119 keywords to describe the behavior of a host
when the value of the 'O' flag remains unchanged. The text in section
5.5.3 needs to be updated to:
If the value of OtherConfigFlag changes from FALSE to
TRUE, the host MUST invoke the stateful autoconfiguration
protocol [...]
If the value of the OtherConfigFlag changes from TRUE
to FALSE, the host SHOULD continue running the stateful
address autoconfiguration protocol [...]
- Ralph
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