Re: [shim6] Exit selection [New Version Notification - draft-mrw-nat66-08.txt]
Geoff Huston <gih@apnic.net> Sun, 13 March 2011 23:20 UTC
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From: Geoff Huston <gih@apnic.net>
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Date: Mon, 14 Mar 2011 10:22:03 +1100
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To: Brian E Carpenter <brian.e.carpenter@gmail.com>
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Cc: "S.P.Zeidler" <spz@serpens.de>, shim6-wg <shim6@ietf.org>, Scott Brim <scott.brim@gmail.com>, Ralph Droms <rdroms.ietf@gmail.com>
Subject: Re: [shim6] Exit selection [New Version Notification - draft-mrw-nat66-08.txt]
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On 14/03/2011, at 9:32 AM, Brian E Carpenter wrote: > On 2011-03-14 10:14, Geoff Huston wrote: >> On 13/03/2011, at 3:32 AM, Rémi Després wrote: >> >>> Le 11 mars 2011 à 20:13, Scott W Brim a écrit : >>> >>>> Shim6 itself cannot select an exit. In all but trivial >>>> cases the network has the intelligence and must be >>>> involved (e.g. the exit points). Given that one has to >>>> involve the network, then an exit selection mechanism is >>>> not just for Shim6 but for anything that can take >>>> advantage of multiple src+dst pairs, and it should not be >>>> Shim6-specific. Therefore whatever needs doing, I >>>> recommend that it not be done in Shim6 but somewhere more >>>> general -- IntArea WG looks like a good place. >>> +1 >>> >> >> wg co-chair hat OFF >> >> I appreciate that in the context of the IETF saying "we >> should not do this" is invariably like standing in front of a >> bulldozer, and like the bulldozer, it rarely has any effect - >> but nevertheless I want to share with you a personal opinion >> that we should not do this! :-) > > If by "we" you mean the shim6 WG, I'm inclined to agree, > beyond documenting that this problem needs to be solved > generically for IPv6. As might be evident from my positing I'm of the view that this is a case of "nothing to see here, move along" and therefore I personally disagree that this "problem" needs to be solved. (but I also appreciate that in the IETF this never works and the IETF is often more obsessed with the rathole than the larger landscape. :-) > I don't believe shim6 is really a > special case: once you have prefixes from and exits to several > different ISPs, you have a potential problem. > >> >> I have two problems with this issue of "exit selection". >> >> Firstly, I recall the demise of the site-local scoped address >> in IPv6. The compelling argument for me was one of inability >> of self-awareness of context. i.e. it was never clear where >> the edge of a site actually lay. So let me replay the same >> problem statement here - what is an "exit" and how does a >> packet know when it has gone through it? And how does a >> router "know" its the exit router and not an interior router? >> In the context of nested sites (e.g. workgroup, department, >> faculty) whats _the_ exit? > > The host and the departmental router cannot know the answer to > that question, I fear, without erecting some very complicated > machinery. > That's my understanding of the situation! >> >> Secondly, its not just the problem of scope of a site here. >> Its also trying to clearly understand the nature of the >> problem and place that into juxtaposition with the various >> proposed "solutions." From memory the various exit selection >> solutions proposed in the context of shim6 were all various >> forms of source-address based forwarding, and for me its >> getting the cart well and truly before the horse. Hop-by-hop >> stateless destination-based forwarding is an incredibly >> powerful architectural concept in packet networks, and any >> other forwarding mechanism tends to invoke copious quantities >> of complexity and state, and should only be contemplated as a >> last resort of the desperate rather than the first line >> solution. > > I fully agree. That would be baroque, and despite having started > this conversation, I am not in favour of a host-based or even > departmental-router-based solution. > >> So why was exit selection an issue in shim6? Surely >> if routing is working, and shim6 does not assume broken >> routing, if a route to a destination is offered, then its a >> valid route. So why select exits that are not being offered >> by routing as being on the best path? From my memory I >> believe it was because some folk thought that a) unicast >> reverse route filtering would be prevalent in IPv6 and that >> b) clients could not negotiate filters with their provider. >> But is a) true? and is b) really true? > > Well, it seems from other responses that both are real problems, > but not specific to shim6. draft-v6ops-multihoming-without-nat66 > talks about this, and at first sight, a valid approach for > the problems described in that draft would work just fine for > shim6 too. Maybe shim6 people should read that draft carefully. indeed, Geoff
- [shim6] Exit selection [New Version Notification … Brian E Carpenter
- Re: [shim6] Exit selection [New Version Notificat… marcelo bagnulo braun
- Re: [shim6] Exit selection [New Version Notificat… Sébastien Barré
- Re: [shim6] Exit selection [New Version Notificat… Brian E Carpenter
- Re: [shim6] Exit selection [New Version Notificat… Rémi Després
- Re: [shim6] Exit selection [New Version Notificat… Scott W Brim
- Re: [shim6] Exit selection [New Version Notificat… Brian E Carpenter
- Re: [shim6] Exit selection [New Version Notificat… Scott W Brim
- Re: [shim6] Exit selection [New Version Notificat… Rémi Després
- Re: [shim6] Exit selection [New Version Notificat… Geoff Huston
- Re: [shim6] Exit selection [New Version Notificat… Sander Steffann
- Re: [shim6] Exit selection [New Version Notificat… Brian E Carpenter
- Re: [shim6] Exit selection [New Version Notificat… Geoff Huston
- Re: [shim6] Exit selection [New Version Notificat… Brian E Carpenter
- Re: [shim6] Exit selection [New Version Notificat… Geoff Huston
- Re: [shim6] Exit selection [New Version Notificat… Fred Baker
- Re: [shim6] Exit selection [New Version Notificat… Brian E Carpenter
- Re: [shim6] Exit selection Rémi Després
- Re: [shim6] Exit selection [New Version Notificat… Rémi Després