This note offers comments on the technical and operational aspects of the proposal for large-scale use of "address leasing" as proposed in: "On the Implications of Address Ownership for Internet Routing", I-D draft-ietf-cidrd-ownership-01.txt, by Rekhter & Li. The draft has been produced within the cidrd working group and is intended for publication as a Best Current Practises official IETF document. I'm copying the message to several lists due to: o the likely short general review that will be possible once the draft leaves the working group, o the types of concerns I raise in this note, o the likelihood of widespread impact from the proposal, and o the simultaneous discussion of related issues on those mailing lists, but I request that any discussion of my comments take place solely on the cidrd mailing list. Comments follow the document's section headings: 1 Abstract Paragraph 2 offers the document as a treatise or review of issues, citing a "focus" on one approach. The primary principle that the paper observes is that flat address spaces don't scale well. In fact the paper is simply a direct proposal for a particular scheme and should be characterized as such. It makes no effort to consider alternatives other than flat addressing nor even to consider the full impact of its recommended scheme. The title of the paper is not helpful and may well be misleading. It introduces the concept of address "leasing", rather than only discussing some drawbacks to permanent "ownership". Hence I suggest that the title of the paper be changed to something like "Proposal for General Use of Address Prefix Leasing". 2 Address allocation Paragraph 3 appears to claim that address ownership has not actually been the policy for more than 15 years and therefore implies that the idea of address leasing is not new and frankly experimental. This is at best incorrect and at worst misleading. For more than 15 years user sites have been given permanent network numbers and have been free to attach via any available provider using those numbers. It is only quite recently that providers have begun to require use of CIDR space and/or change addresses when changing providers. The paper should not attempt to suggest to the reader that leasing is anything other than a fundamental change in Internet address administration policy. As such, the paper should acknowledge and emphasize the frankly experimental nature of leasing done on a global scale. (Yes, I did say experimental. Contrary to the comments on the cidrd mailing list there has been no large scale use of a leasing policy and no real analysis of its effect. When claims are made to the contrary, they seem to hinge on a) the lack of changes needed for the large transit providers and their routers and b) a long history of organizations occasionally changing their IP network numbers, albeit mostly painfully. A side effect of this is that some other schemes which have been handily dismissed as experimental probably warrant more substantive consideration. One more presumption that warrants attention is that the Internet does not have time to consider alternatives. The facile counter to this concern is to ask whether the Internet has time to see CIDR and address leasing fail, eliminate local providers, or otherwise kill the Internet?) 3 Addressing and routing (no comments) 4 Address ownership Paragraph 4 refers to "space complexity" -- which I seems to mean the amount of space required -- for "the different schemes". Which schemes? The paper only discusses totally flat and totally hierarchical schemes. Is this total of 2 schemes what is being cited? In the next paragraph the paper states the importance of having an address reflect the topology of the network. Since the Internet is not a tree, but instead is a messy mesh one must ask by what procrustean process the Internet topology is to be represented by (relatively) stable hierarchical addresses? It is certainly true that a graph can be represented as a tree by taking a particular view of it but that representation only holds from that view. Such a view is applicable to snapshots needed when making routing decisions but not for globally-absolute addressing. The paper also says that changing an address is required as the network topology changes. This simply isn't true or, at least, is not what is being done or proposed. Internet topology changes all the time and sites are not required to change their addresses. At best this paragraph is seriously imprecise. At worst it is seriously wrong. The end effect is to aid in the myth of Internet topological hierarchy. We need to reverse this misleading view. The seventh paragraph discusses routing table exceptions. (The second sentence is awkward and should be re-written.) Exceptions are those entries which do not conform to the hierarchical model. The paragraph acknowledges that the Internet isn't strictly hierarchical but it then entirely misses the implication. For example it fails to note the effect of large-scale occurrence of multi-homing by local providers and users. (During discussions, the CIDR document has been referenced for its consideration of multi-homing. In fact that consideration clearly presumes that there IS a legitimate hierarchy in the Internet, which presumption no longer applies.) The last paragraph in the section makes quick mention of a possible impact on organizations which "sub-lease" numbers. This means that a local provider which changes transit providers will be forced to force its customers to renumber! While large transit providers well might not view this impact as substantial I suggest that it is, in fact, quite serious and deserves rather more discussion. For example CIDR and address leasing is likely to create a basic barrier to entry for local providers. ("Barrier to entry" is offered as a euphemism for "put all of them out of business.") They might not approve of such an effect. 5 Recommendations The first paragraph contains the disclaimer "Existing address assignments and allocations are outside the scope of this document." However the handling of existing addresses has very much been a part of working group discussions and appears to be very much a part of the intent behind pursuit of the address leasing model. In particular, working group discussions have cited CIDR as no longer being adequate when applied for new addresses only and that "recovering" existing addresses is required. Please note that I said "required". That, at least, is the message that has been communicated in recent working group discussions. If that message is wrong then we need to hear rather clearer explanations for the near-term need to promulgate a leasing policy. The proposal needs to attend to this issue directly and should not pretend that it is anything other than an immediate and pressing concern. The next-to-last paragraph acknowledges that users might incur some cost when renumbering, but the paragraph elides further discussion of the issue, instead simply saying that organizations need to consider tradeoffs. I suggest that a paper which is proposing a major change for the Internet is obligated to offer rather more detail about its impact and rather more concrete information for considering tradeoffs. It needs to list and discuss those tradeoffs. At the least that will demonstrate detailed understanding of the proposed policy's impact. The last paragraph cites DHCP. It appears to suggest that renumbering tools are a) adequate, and b) adequately deployed. The paper needs to discuss both of these assumptions in detail, particularly since there is a substantial constituency which believes that both assumptions are entirely incorrect. 6 Conclusions The first paragraph cites concerns for routing system scaling. However there is no concern expressed for Internet local providers or users. The paper needs substantial enhancement to consider the breadth of the proposal's effect. In fact I strongly urge than any proposal which attempts major change to the Internet -- as does this one -- be required to offer an operational "environmental impact statement." Equally strongly I suggest that this include a transition plan, as we require for other, equally massive changes. -------------------- Dave Crocker +1 408 246 8253 Brandenburg Consulting fax: +1 408 249 6205 675 Spruce Dr. page: +1 408 581 1174 Sunnyvale, CA 94086 USA dcrocker@brandenburg.com