-----Original Message----- From: ietf-bounces@xxxxxxxx [mailto:ietf-bounces@xxxxxxxx] On Behalf Of Jari Arkko Sent: Thursday, September 22, 2011 2:35 PM To: ietf@xxxxxxxx; draft-weil-shared-transition-space-request@xxxxxxxxxxxxxx Subject: Re: Last Call: <draft-weil-shared-transition-space-request-03.txt> (IANA Reserved IPv4 Prefix for Shared Transition Space) to Informational RFC So here's what I would like to propose. The document goes forward but we make a much clearer statement with regards to the implications both for applications out there, as well as for subsequent IETF work: - what types of impacts may be felt by the rest of the network (not the ISP that is deploying NAT444) - what kinds of application practices may be affected - what IETF specifications may need revision due to this (e.g., do we need to revise ICE etc) Jari - It's unclear from your statement if you're proposing adding the above to this draft or to a subsequent draft. To respond to your concerns and recommendation, I think that there are three separate issues here that merit some discussion: 1) Does IETF recommend the practice of inferring address scope in IPv4 based on address/bit value (the actual numbers), and then using this to trigger different behavior based on that inferred scope? 2) Should draft-weil or draft-bdgks or both be formal updates to RFC1918 as additional private-scope use cases? 3) Independent of consensus on the state of the *draft* directing it to happen, is there consensus on the *idea* that the /10 of IPv4 space should be reserved as shared transition space? My own opinion on each question: 1) We do link the scope and bit values pretty closely in IPv6. Multicast (Class D) is definitely a scope link, and RFC6250 doesn't say otherwise, though it would have been a recent opportunity to clarify our position. My sense is that there are a number of standards (notably 3056) that recommend specific behavior when private-scope or non-unique addresses are used, but the terms "behind a NAT", "RFC1918 addresses" and "private addresses" are often used interchangeably, thus reinforcing this link between scope and value. However, draft-bdkgs section 4.1.2 implies that this is not a valid assumption to make, but your concerns over what breaks and how to test support the idea of a link, which is why I bring up the question. I think that it might be useful to formalize this link, but I'm not sure if that belongs in these drafts, and I don't think that it's gating to them moving forward. 2) I really believe that one or both drafts should either be an update or -bis document for RFC1918. I believe that they are in essence documenting additional use cases for private scope address that are beyond what was covered in RFC1918, with the added requirement that they cannot conflict with the existing space. While the address space and use cases are not interchangeable for reasons documented in draft-bdgks, most of the same considerations regarding usage (how not to break things) apply to both. Formally updating RFC1918 would at least give implementers a warning that there is new space to test for wherever 1918 is referenced in an existing standard and should therefore address your concern. Based on your proposal, if we don't formally update 1918, we end up having to go through existing standards to find places where the authors used RFC1918 interchangeably with "non-unique addresses" or "private-scope address space". We would then have to evaluate if they used this as an indicator to recommend a different behavior in cases where one can infer the address scope based on the bit value and decide whether those cases apply to this new space or not. I think that using 1918 as a baseline and only documenting items which are unique considerations for this space and application represents a lot less work than what you're proposing above, whether it's part of this draft or its own work. 3) The reason I bring up consensus for the idea rather than the document is that there seems to be some urgency behind getting *something* approved to make the allocation happen, but it seems to be driving this strange behavior to push through incomplete documents and sort out the details in subsequent drafts. Assuming that it is in fact necessary to get the allocation completed rapidly, I'd rather see us split the logistics of making that happen from the process required to produce consensus documents. This may be as simple as IAB or IESG giving ARIN (and/or IANA) provisional clearance to allocate or reserve the space on the belief that there is consensus to make the reservation, but that we want our documentation in order before it is made public for use. That removes any pressure to push the documents through before they are ready, while still ensuring that the address space is available when we are happy with the documentation. If for some reason the document fails to achieve consensus in its final form, there's no harm in then telling ARIN that they must release the reservation. Additionally, if we're talking about pushing draft-weil back for that much analysis, we're now talking about a non-trivial delay, and in that case it may make sense to simply put the two drafts back together since weil was supposed to go through quickly as a minimal draft with bdgks being the one that the community spent more time on to ensure completeness and consensus. 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