JoaoBR wrote:

The thing is, source selection policy and IP address scope blow the assumptions in this discussion out of the water, as does the concept of unnumbered IP interfaces.

Scoping and selection policy is necessary to support link-local IPv4 (Zeroconf) and IPv6 as we move swiftly into a world where these things are a fact of life, and make deployment of useful IP networks for non computer users a reality. Interface preference is desirable in a stack supporting multipathing.

Unnumbered IP, for example, is not dealt with at all well by the BSD stack. There are situations in which it is perfectly valid; a newly booting machine; a router at the end of a PPP link. We deal with something like 30% of the problem space for unnumbered IP. We need to be able to tell the IP stack 'be attached to this interface without a configured IP'.

ifconfig syntax currently doesn't capture this requirement; the keywords 'add/delete' are closer to this intent. In the meantime, attachment of an address family to an ifnet in the kernel depends upon having at least one address configured, therefore 'alias/-alias' is the best fit to the current reality of the code.

I look forward to seeing patches as a result of this discussion if anybody actually wishes to change anything.

Regards, BMS