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Re: Temporary IPv6 addresses vs. netgroups

    Date:        Thu, 31 Jan 2013 21:57:17 +1100
    From:        Darren Reed <>
    Message-ID:  <>

  | How do you define "local address" in this context?
  | Is it just something from a RFC1918 address space or...?

Personally I'm most concerned with IPv6, rather than IPv4 (which is,
or should be, on its way to extinction, so wasting more effort on
solving its problems is pointless) - in the v6 context, a local address
is something from the FC00::/7 address block.   But those are about as
close as v6 comes to 1918 addresses, so I guess, yes.

The relevant criteria is that we can use them to communicate with some
destinations, but not others (1918 in v4 world mostly fails that test
because of NAT).  For the others only global addresses work.

  | The point here being that some organisations have large
  | internal networks where a local address is usable on a
  | network with a bredth of 10 or more hops.

Sure, and if we ever actually implemented apps that attempt to use local
addresses where possible (that is, by their own initiative, rather than
being human configured) then we'd need to be able to configure the criteria
used for deciding when an address might be local (which would include how big
a hop limit to attempt, and how long to wait for replies).

Until v6 is in enough use that people actually start getting global addresses
renumbered on them, most likely no-one will care enough about this issue
to bother with attempts to find solutions.   Slightly regrettable, but totally
understandable.   My objective in all of this is simply to see if we can end
up with an API that would allow this kind of thing to be done, when (or if)
it ever turns out to be useful enough to spend cycles implementing.


ps: I agree with you that being able to  give interfaces some kind of
preferences would be useful, but I also agree with Ignatios that this is
a different problem than the one we have been discussing.

pps: the old v6 "site local" addresses were better than the current local
addresses for the purposes discussed above, as they had the notion of a
site boundary, and a "going out of scope" ICMP - with those, detection of
when a (site) local address can be used was much much easier.

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