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Re: Temporary IPv6 addresses vs. netgroups

>> In general, bind(2) it before connect(2)ing. 

> That can work, provided the application supports it, but is really a
> terrible solution -

Unfortunately I think it's the only solution, not only just because we
don't have any APIs more sophisicated but because it's not an easy

> the application doesn't really care which address gets used, just the
> type of address.

Perhaps, but "type" is somewhat ill-defined here.  One application's
idea of address type doesn't necessarily match the next's.  One may
prefer "site-local reachable over this VPN tunnel" over "globally
routed" over "other site-local", as a simple example that is unlikely
to match any notion of "type" that's likely to make it into an API.

> A multi-homed host (which is getting to be far more common) wants
> some applications to use temporary addresses, and others to use
> stable addresses (and if we had them, perhaps others to use CGAs)

...and potentially other criteria, too complex to represent simply...

> but doesn't really want to do all the work of selecting which
> particular temporary address (ie: which outgoing interface) is the
> appropriate one for each destination.  The kernel already does that,
> and selects an associated address, it should just continue doing
> that.

Trouble is, that's suitable only when the kernel's preference rules
match the application's.  Since different applications want different
rules, the application has to control local address selection somehow.

And I think we agree on that much.  But it seems to me that an API that
classifies addresses into some small number of types based on
set-in-stone rules is going to be useful to too small a subset of
applications to make it worth the various costs of adding it.  I would
prefer to do this in userland, with a library routine that fetches the
list of addresses and selects one based on whatever criteria it wants,
maybe even involving an application-provided callback.

And, shouldn't this be on tech-net?

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