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Re: source address rewriting and shim6 proxies
marcelo bagnulo braun wrote:
what difficulties am i missing?
The first one is that we don't know what problem we are trying to solve
with shim proxies. It could be enabling legacy IPv6 hosts behind a proxy
(this is what Paul is suggesting as far as I understand), or it could be
having shim aware hosts offload some functionality to a shim proxy.
The issues with the two are quite different. So which one are we trying
Your comments were related to the second problem:
I am not sure i can see any difficulty with this... I mean in current
multihomed site scenario, where the prefixes are quite stable and they
change because of renumbering events associated to changes in the ISPs,
the coordination of the prefix set perceived by the host and the prefix
used by the routers seems feasible to me... In more dynamic scenarios,
this may be require further analysis.
But this might be problematic if you have shim6 hosts with different
capabilities. For instance, a smallish host is today allowed to not
configure IPv6 addresses for all the prefixes announced on its links,
which it might do to save on memory (think small battery operated devices).
Having the routers be configured to rewrite to any of the site's
prefixes would then mean that the peer would see packets with a source
locator which was not setup as part of the context.
Even if you want to ignore small (battery operated) IPv6 devices, you
have similar issues when the set of prefixes change; the border routers
notion of the prefixes to use will be out of synch with what any
particular host in the site knows as the prefixes.
One way to handle this is to have the receiver, instead of looking up
the context based on <source locator, destination locator, context tag>,
only use <destination locator, context tag> for the lookup. That way if
the border routers put in a source locator that the source host isn't
aware of, the packets still get accepted by the destination.
But as I said, I don't think this is the problem that folks are trying
to solve with the external shim.