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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
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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