Comment 15 for bug 1435283

The current way we pick public / private addresses for a unit looks for the "best match" for the requested scope (public / private) and type (ipv4 / ipv6) - allowing fallbacks if an exact match isn't available.

So we can't just switch to picking one and always returning that, as an exact match might not be available the *first time* we're asked - but an exact match may become available later.

My suggestion is to switch to something like the following:

First time we're asked for an address we use the current algorithm to find the best match on scope and type. Whatever is found we store as the "default address" (we will store a default public and a default private address).
On subsequent requests check if the stored default is an exact match (and still available) for the requested scope / type.
If it is still available and an exact match we just return it.
If it is no longer available we remove the default and start again (we'll address using the same NIC for changed addresses at another point as that's more complex).
If it is still available, but it wasn't an exact match and an exact match is now available - we replace the current default with the exact match and return that. Subsequent requests will now always see the new default.

How does this sound Ed?