On Apr 23, 2005, at 12:51 AM, Jonathan Stone wrote:

> Try intsead to articulate what you *actually* want.

Let me articulate what *I* want, in abstract terms, so we can get  
away from the implementation details.

I want the source address of an outgoing packet to have the same  
"scope" as the destination address, when possible.

Let me provide some examples:

If I am talking to an IPv4 link local address (e.g. zeroconf), then I  
want the source address to be my IPv4 link local address.  If I don't  
have a link local address, then obviously I have to pick something  
else as the source address.

If I am not talking to an IPv4 link local address, then I do not want  
to pick my IPv4 link local address as the source address.  If I only  
have an IPv4 link local address, then obviously I have to use it, and  
hope that my NAT does the right thing (e.g. a zeroconf wireless  
network where the base station NATs the wireless IPv4 link local  
addresses to a routable address).

-- thorpej