> I think the above paragraph is unneeded and confuses the issue.
> Setting the flags to 0 will restore the system default behavior.
> If the app is using multiple values at different times, the behavior
> is really up to the app, and the issue is not specific to this
> socket option. RFC 2553 etc do not contain a similar statement
> for other socket options which have the same issue. I'd suggest
> deleting this paragraph.
The issue is that by having PREFER_FOO and PREFER_NOTFOO flags
is that the absense of having any of PREFER_FOO and PREFR_NOTFOO flags
set in a setsockopt nothing about the "foo" state can change.
If it did change they the application couldn't change the state for bar
independently of foo.
A result of this is that a setsockopt with zero flags can have no effect.
So unless we change the approach we'd need a separate mechanism for
resetting to the default.
> If someone implements Mobile IPv4, wouldn't the HOME/COA flags
> be applicable to IPv4 source addresses?
Could be. We can relax this to allow it to work for IPv4.
> I agree "require" flags would be nice. For example, if an app requires
> a particular type of address and there are no such addresses available,
> it may be better to fail the setsockopt than either failing all sends or
> using another type of address instead.
With the complications that some failures will appear late e.g. due to
a source address of the type not (or no longer) being available on
the outbound interface.
Another complication is that I don't know what it means to
say REQUIRE_HOA or REQUIRE_COA if the node isn't
currently mobile or when it is at home.
The softer notion of preferences avoids this, but addition
validation ("is this address a HoA") adds that complication
back in I think.
Erik
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