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

[Olivier Bonaventure <Bonaventure@info.ucl.ac.be>]

Erik,
> >     Have folks seen Jason Schiller's slides from NANOG 35?
> >     Might be useful to review those for some of the issues
> >     that (some set of) providers are seeing:
> >
> >     http://www.nanog.org/mtg-0510/pdf/schiller.bof.pdf
>
>
> It would actually be useful for somebody to do the exercise of 
> determining which issues are fundamental because each site has multiple 
> prefixes, and what issues are specific to shim6.
>
> For instance, even in GSE the host selects which of multiple destination 
> addresses to use, at least for the initial packet exchange.
> But in GSE the host doesn't select the source address; the border 
> routers set the source address.
>
> 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.

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

Letting hosts select paths in multihomed scenarios where a enduser is 
attached to both ADSL and CATV networks is useful. However, if the host 
belongs to an entreprise network, then the managers of the entreprise 
network will probably want to influence the selection of the source and 
destination locators. One possibility to do this would be to tune the 
DNS servers (assuming the hosts perform DNS requests before sending 
data) or define a protocol, used in the entreprise network to perform 
the address selection on behalf of the endsystem. Such a protocol was 
proposed a few years ago :

http://www2.info.ucl.ac.be/people/delaunoi/ietf/draft-de-launois-multi6-naros-00.txt

Letting hosts detect failures is a nice approach in the ADSL+CATV 
environment. In an entreprise network, the border router could receive 
information about the failure (e.g. reception of BGP withdraw) and 
inform the endsystems in the network.

I think that shim6 will have to consider issues that arise when 
thousands of multihomed hosts are in the same entreprise or campus network.


Best regards


Olivier
--
CSE Dept. UCL, Belgium - http://www.info.ucl.ac.be/people/OBO/