[Babel-users] sorting out the right ipv6 addr to choose and name in a source specific world

[Juliusz Chroboczek]

> The ideal scenario is where the host app picks the "best" address for
> each connection type, and I am a little vague on what actually
> happens. What my backbrain (but not RFC 3484 - is there a later rfc
> for what gai.conf should do?)

With ordinary next-hop routing, routing policy is entirely in the
routers -- the end hosts have no control whatsoever on the path taken.
The opposite of source routing, where the hosts have the ultimate control
on routing policy, and the routers merely provide a mechanism [1].

Now source-specific routing is an interesting compromise between the two:
it splits policy decisions between the routers (who distribute a set of
source-specific routes) and the hosts (who pick among one of the available
routes by specifying a given source address).  But even though the amount
of policy control given to hosts is fairly modest, it still requires that
some routing intelligence be implemented within the hosts -- and, as you
justly note, the available mechanisms are insufficient.

I think we're pretty much done with the routing part -- I'm fairly
confident now that we've got a reasonable understanding of source-specific
routing in edge networks [2,3].  On the other hand, we haven't done any
serious work on the host side of things -- if anyone understands how to
distribute source address selection policies in a way that is both fully
automated and flexible enough, they're not saying.  (And I'm pretty sure
that DNS is the wrong place to do that.)

[1] J. Saltzer, D. Reed, D. Clark.  Source-routing for Campus-wide
    Internet Transport.  1980.
    http://groups.csail.mit.edu/ana/Publications/PubPDFs/SourceRouting.html
[2] M. Boutier, J. Chroboczek.  Source-specific routing.  2014.
    https://hal.archives-ouvertes.fr/hal-00947234v3
    (Yes, it's a new version.)
[3] As opposed to core networks, where there's the ugly issue of routing
    table explosion -- please give Matthieu a core network to break)

-- Juliusz