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
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:
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
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
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
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
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.
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.
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.