Desired behaviour of "ifconfig -alias"
Bruce M. Simpson
bms at FreeBSD.org
Tue Feb 13 13:17:33 UTC 2007
> The only correct thing you say here is that all IPs are equal - and - nobody
> EVER said something different.
> Aliasing does not say anything about priority of the Ip it is simply related
> to the time the interface was set with the IP so the first IP is the one
> which was set first and the first alias is the one which was set after.
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
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
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.
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