Re: TE & SHIM6 (was Re: comments on draft-ietf-shim6-proto-03

[Tony Li <tony.li@tony.li>]

>> I don't think we are very far away from allowing the routers to change
>> the source locator in shim6, but I don't feel we collectively
>> (IETF+NANOG etc) know how useful such a capability would be.
> 
> I'm not convinced that letting routers change the source locator in
> shim6 would be a good solution. This will add new mechanisms on the
> routers, force them to maintain some additional state and could lead to
> a NATification of IPv6.


Shim6 is a NATification of IPv6 anyway, it just colocates the NAT
function with the individual host.

Letting the routers change the the source locator turns out to be very,
very useful in aiding the access ISP in doing source address filtering.
   Without that, we have the choice of unintentionally sending packets
with an inappropriate source locator to our access ISP, or warping our
IGP's and forwarding algorithms to work based on the source locator.
The latter is a major shift away from where IP has been since 1983.


> Despite this, I have the impression that the IETF did not consider
> entreprise or ISP networks when developping shim6. The basic assumption
> has been that hosts perform all decisions related to shim6 autonomously
> - host select the source and destination locators
> - host check the availability of the path and switch to another one in
> case of problems


Let me try to correct your impression.  Some of us are very much aware
of the issues involved and are very interested in supporting more
functionality at the enterprise boundary.  However, over the years, it
has been made very clear that performing that type of locator selection
or route selection at the enterprise border is also seen very much as a
form of NAT.

While I happen to disagree with that particular assessment, the simple
fact of the matter is that the political situation within the IETF at
present makes any non-host-based solution intractable.  This is
_precisely_ what drove us towards the shim6 solution.  It is not an
optimal answer, by any means, IMHO.  It is only the best solution that
we have been able to reach consensus on.

Regards,
Tony