[arin-announce] [arin-ppml] Multihomed Microallocations

Member Services info at arin.net
Tue Aug 4 11:03:44 EDT 2009

The following is a new policy proposal that has been posted to the ARIN
Public Policy Mailing List for discussion on that list.


Member Services
American Registry for Internet Numbers (ARIN)

## * ##

Member Services wrote:
> ARIN received the following policy proposal and is posting it to the
> Public Policy Mailing List (PPML) in accordance with Policy Development
> Process.
> This proposal is in the first stage of the Policy Development Process.
> ARIN staff will perform the Clarity and Understanding step. Staff does
> not evaluate the proposal at this time, their goal is to make sure that
> they understand the proposal and believe the community will as well.
> Staff will report their results to the ARIN Advisory Council (AC) within
> 10 days.
> The AC will review the proposal at their next regularly scheduled
> meeting (if the period before the next regularly scheduled meeting is
> less than 10 days, then the period may be extended to the subsequent
> regularly scheduled meeting). The AC will decide how to utilize the
> proposal and announce the decision to the PPML.
> In the meantime, the AC invites everyone to comment on the proposal on
> the PPML, particularly their support or non-support and the reasoning
> behind their opinion. Such participation contributes to a thorough
> vetting and provides important guidance to the AC in their deliberations.
> The ARIN Policy Development Process can be found at:
> https://www.arin.net/policy/pdp.html
> Mailing list subscription information can be found
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> Regards,
> Member Services
> American Registry for Internet Numbers (ARIN)
> ## * ##
> William Herrin wrote:
>> 1. Policy Proposal Name: Multihomed Microallocations
>> 2. Proposal Originator: William Herrin
>>   3. Proposal Version: 1.0
>> 4. Date: 3 August 2009
>> 5. Proposal type: new
>> 6. Policy term: permanent
>> 7. Policy statement:
>> 4.4 IPv4 Allocations and Assignments to Small Multihomed Organizations
>> 4.4.1 Section 4.4 specifies criteria for allocating /23 and /24 IPv4
>> address blocks to end users and ISPs where the requesting organization
>> is multihomed with multiple Internet vendors but does not meet the
>> minimum usage criteria for address allocation or assignment under
>> Sections 4.2 and 4.3.
>> 4.4.2 Except as specified in section 4.4, the requesting organization
>> must also meet all criteria for receiving addresses specified in
>> section 4.2 if an ISP or section 4.3 if an end user.
>> 4.4.3 Criteria for allocation or assignment
>> The requesting organization must hold exactly one AS number
>> and must already announce IPv4 addresses to the Internet via BGP using
>> its AS number.
>> The requesting organization must announce IPv4 addresses to
>> the Internet via at least two distinct Internet vendors.
>> The requesting organization must spend at least $8000/year on
>> the Internet services in
>> Upon annual renewal of the allocation or assignment received
>> under section 4.4, if the requesting organization fails to demonstrate
>> that it continues to announce IPv4 addresses to the Internet via at
>> least two distinct Internet vendors the allocation or assignment is
>> revoked and returned to ARIN.
>> The requesting organization must agree to withdraw any other
>> BGP routes it announces from the BGP table within 6 months of
>> receiving an allocation or assignment under section 4.4. If the
>> organization continues to receive IP addresses from its ISPs, those IP
>> addresses will be single-homed within the ISP's larger aggregate
>> announcement.
>> If the requesting organization fails to announce the
>> allocation or assignment received under section 4.4 to the Internet
>> using its AS number for at least 4 months total within a service year,
>> the allocation or assignment is revoked and returned to ARIN.
>> If the requesting organization already holds IPv4 addresses
>> directly from ARIN, from any other RIR or legacy addresses, the
>> organization must agree to renumber out of those addresses and
>> surrender them to the appropriate RIR within 6 months of receiving an
>> allocation or assignment under section 4.4.
>> The requesting organization agrees to return the allocation
>> or assignment received under section 4.4 to ARIN within 6 months of
>> receiving another allocation or assignment from any RIR.
>> For allocations of /23 and larger, the requesting
>> organization shall meet the utilization rate criteria described in
>> section 4.2 for ISPs and section 4.3 for end users. As /24 is the
>> smallest address block known to be generally routable on the Internet,
>> no utilization criteria will be applied to requests for a /24.
>> 8. Rationale
>> The reason behind a /20 minimum assignment for single-homed orgs is
>> fairly straightforward: an ARIN allocation adds a route to the BGP
>> table which wouldn't otherwise be needed. Routes are expensive and the
>> cost falls into overhead since it isn't recoverable directly from the
>> org announcing the route. And we're not really certain how many routes
>> we can handle before the network falls over. So, we restrict the
>> availability of non-aggregable IP addresses to just very large
>> organizations. For smaller orgs, renumbering sucks but at least it
>> only costs the renumbering org, not everyone else.
>> The reason behind nothing smaller than a /24 is also straightforward:
>> many if not most ISPs filter out BGP announcements smaller than /24.
>> There is tremendous inertia behind /24 as the minimum
>> backbone-routable quantity going back to the pre-CIDR days of class-C
>> addresses. So, an ARIN allocation smaller than /24 would generally be
>> wasted addresses, unusable on the Internet.
>> But why peg multihomed orgs at /22 instead of /24? Multivendor
>> multihomed orgs have to announce a route anyway, regardless of whether
>> the addresses are from an ISP or directly from ARIN. Their routes are
>> not aggregable, even if assigned from ISP space. That's the way the
>> technology works and no new tech in the pipeline is likely to change
>> it.
>> With load balanced server clusters and NAT you can pack a heck of a
>> lot of punch into a multihomed /24 if you want to. And as a community
>> it's to our benefit to want registrants to pack the maximum punch into
>> their address space: IPv4 addresses are becoming scarce. So why
>> restrict ARIN assignments to folks who can write papers which justify
>> a /22?
>> FAQ
>> Q. Why not just use ISP addresses if you're too small?
>> A1. ISPs have conflicting requirements placed on their use of IP
>> addresses. They want, for example, to prevent address spoofing at
>> their borders by not allowing traffic from their addresses to enter
>> their network from another ISP. These goals conflict with multivendor
>> multihoming and generally make a mess when a customer wants to
>> multihome.
>> A2. Renumbering is expensive and painful. We should require it only
>> when it serves a reasonable public policy goal such as reducing the
>> consumption of BGP routing slots.
>> A3. We've seen common counterproductive situations where multihomed
>> end users make many discontiguous /24 announcements until they
>> eventually seek ARIN address space.
>> Q. But aren't your routes aggregable with your ISP's routes if you use
>> your ISP's address space?
>> A. No. For routes to be aggregable, two things must be true:
>> 1. The routes must be contiguous, sharing a common network/netmask.
>> 2. The routes must share an identical network topology.
>> In the mutlivendor multihomed case addressed by this proposal, the
>> routes almost never share an identical network topology. As a result
>> the routes can not be aggregated even if cut from the ISP's address
>> space. Single-homed networks are excluded from this proposal precisely
>> because they always share a network topology with the ISP.
>> Q. Can't other organizations filter routes at the RIR minimums and
>> user the ISP's covering route to reach you?
>> A. Maybe. With a bunch of ifs. You might not be connected to the ISP
>> who has the covering route, and what if he doesn't have the more
>> specific route to you?
>> The answer is more decisive on a practical level: The author was
>> unable to identify any ISPs who presently both filters on RIR minimums
>> and chooses not to carry a default route to an upstream ISP that
>> doesn't filter. Hence there is no apparent route filtering value to
>> the RIR minimums.
>> Q. What's so messy about multihoming with a cutout from an ISP's
>> allocation?
>> A. Many things. Here are some of them:
>> * As an ISP I want to drop packets from the Internet that purport to
>> be from my addresses (spoofed packets). I can't do that with packets
>> from a multihomed network: in the normal course of failure recovery or
>> traffic engineering, the multihomed user may originate packets to
>> hosts on my network using the IP addresses I assigned him, but via his
>> other ISPs. These packets will arrive at my Internet interfaces and if
>> I drop them as spoofed packets, I've broken my customer's
>> connectivity.
>> * As an ISP I want to reject false route announcements entering my
>> system which purport to serve my addresses. And I want my pager to go
>> off and let me know someone is trying to hijack my address space. My
>> multihomed customer will, in some circumstances, want me to route all
>> packets to him via his other ISP. That means I have to accept his
>> route announcement from other ISPs. To do this, I have to write some
>> tricky filtering rules that accept his routes right smack in the
>> middle of the address space where I generally want to reject routes.
>> * As an ISP, I want to aggregate my contiguous address space into a
>> single route announcement. It's part of being a good citizen: don't
>> waste the TCAM slots in everybody else's router. But I have to
>> carefully exclude my multihomed customer's routes from that
>> aggregation. Packets follow the more specific route. If he announces
>> his more specific route to his other ISP but I roll his route up into
>> my less specific route when I announce it then all his packets will go
>> to his other ISP instead of to me and I won't get paid.
>> * Lots of folks disaggregate their route announcements for the purpose
>> of traffic engineering. Two or three hops away from their system,
>> those TE routes are irrelevant. In theory I should be able to filter a
>> lot of that out by discarding the routes smaller than the RIR minimum
>> allocation for that /8. That would save me money and make my routing
>> updates work faster. But if I try it, I end up filtering mutlihomed
>> customers so that I can only reach them via the ISP that assigned
>> their addresses. At best that damages the effectiveness of my routing.
>> At worst it cuts me off from sites my customers want to access when my
>> competitors who just accept /24 everywhere don't have a problem. Oops.
>> Q. Where do the announced addresses in come from?
>> A. Most likely from one of the ISPs as described in NRPM section
>> You go through the process of getting them assigned and
>> announced to demonstrate that you're not a poser. Then you get
>> addresses from ARIN under this proposal and return the
>> addresses to your ISP.
>> Q. What does "distinct vendors" mean?
>> A. It means two different ISPs like Verizon and Sprint. Two T1s with a
>> single ISP can be accommodated without announcing a route into the
>> Internet backbone, so such a connection does not qualify for addresses
>> under this proposal.
>> Q. $8000? What's that all about?
>> A. The best available estimate of the systemic cost of carrying a
>> route in the Internet backbone table is around $8000/year. See
>> http://bill.herrin.us/network/bgpcost.html for the cost estimate.
>> If you're going to play in the backbone, you should really be putting
>> more money into the system than you're taking out. If you have two
>> $600 T1's then you're spending nearly twice that anyway. This  limits
>> the folks who want to multihome their $50 DSL and cable modems.
>> Q. How reliable is that estimate? Does it change? Shouldn't ARIN
>> routinely update that estimate rather than codifying the specific
>> number in the policy?
>> A. In theory ARIN staff should set the number. In practice,
>> professional cost analysts are expensive and hard data on things like
>> router count is almost impossible to get anyway. Even if a more
>> reliable cost analysis could be produced, we still wouldn't know what
>> multiple of that cost was "fair" for the pay-in. 1x? 2x? 5x? Let's
>> just pick a number that's our best guess at fair, and move forward
>> with it.
>> Besides, the $8k rule will probably turn out to be a non-operative
>> part of the policy. Companies providing $50 DSL service are
>> disinclined to set up BGP sessions with their customers anyway. I
>> include it in the name of caution so that we're proof against a deluge
>> of multihomed cable-modem users but I expect that with some experience
>> under our belts we'll find that we can safely submit a follow-on
>> policy proposal that removes the $8k requirement.
>> Q. I have to renumber when exactly?
>> A. If you have IP addresses under section 4.4, you get to announce
>> that one allocation or assignment to the Internet via BGP. In fact,
>> we'd really prefer that you only announce one single route, even if
>> you get a /23 or larger. You don't get to collect two assignments and
>> then ten discontiguous assignments and burn up the BGP table. Until
>> you reach the minimums in sections 4.2 or 4.3, you renumber each time
>> you grow large enough to justify the next bigger allocation or
>> assignment. Yes, that's unfortunate and painful. But burning up the
>> BGP table would be even more unfortunate.
>> Practically speaking, you'll renumber zero or one times. Either you'll
>> never renumber because the /24 was enough to do the job, or when you
>> run out of space in your original assignment, you'll be big enough to
>> find a way to meet the minimum size criteria in section 4.2 or 4.3 so
>> that you don't have to renumber again.
>> Q. But renumbering is expensive! What's the difference between having
>> to renumber under this proposal and having to renumber when I change
>> ISPs?
>> A. You'll have to renumber less often if at all. The big deal is that
>> you don't have to renumber merely because you changed vendors and you
>> don't run into a sticky mess of   filtering rules as ISPs try to keep
>> control of their address space.
>> Q. Doesn't this discriminate against some kinds of multihoming?
>> A. In addition to multihoming with your own AS number, its possible to
>> have two ISPs separately announce your addresses or announce with a
>> private AS number that they strip from their peer announcements. This
>> proposal is more than complex enough. For the sake of making
>> verification simple, let's just say that tiny registrants will
>> announce with their own AS number, period.
>> Q. Does this proposal affect IPv6 allocations and assignments?
>> A. It does not appear to impact ISP allocations whose criteria is
>> spelled out in NRPM section It does impact end user
>> assignments under NRPM section End users who qualify for
>> addresses under this policy will also be qualified for an IPv6 /48.
>> Q. Have there been previous policy proposals to extend allocations and
>> assignments from ARIN to /24?
>> A. Yes. See the discussions in March and April of 2007 for proposal
>> 2007-6. http://lists.arin.net/pipermail/arin-ppml/
>> In proposal 2007-6, the /22 size for multihomers in section 4.3 was
>> simply changed to /24. It met the following criticisms:
>> * Could make it easier for spammers. This seems to reflect some
>> concern at the time over whether ARIN's policies made things easy for
>> spammers to hop IP addresses and was probably a red herring. Spammers
>> aren't interested in registering with anybody. They want address space
>> as anonymously as possible for as long as possible as cheaply as
>> possible exerting as little effort as possible. All of these things
>> make address space under this proposal unattractive to spammers.
>> * Could create a land rush. This seems like an unreasonable concern
>> for the instant proposal: anyone who can justify addresses under this
>> proposal can justify the same addresses from their ISP already. So why
>> hassle them with ISP addresses?
>> * Could create a new swamp. The renumbering requirements in this
>> proposal prevent that problem.
>> * Unfair to ISPs since it only applies to end users. This proposal
>> applies to both.
>> * Staff worried that it could increase request workload. If it does,
>> the fees could presumably be set accordingly.
>> Proposal 2007-6 also tried to make the following point: Don't penalize
>> the honest. An org that has ponied up the cash to be multihomed with
>> multiple vendors can often restructure their network to require a /22
>> long enough to get one. Refusing ARIN assignments smaller than /22
>> encourages behavior which is contrary to ARIN's general public policy
>> goal of conservation. We'll be better off as a community if the folks
>> who are completely honest about their need get the same or better
>> treatment than the ones who lie.
>> Implementation notes:
>> This proposal asks for verification of multihoming somewhat beyond
>> what the rest of the NRPM requires. It does this in order to prevent a
>> land rush of cheaters. Not that there's likely to be a land rush of
>> cheaters (or if there is that they're likely to ask for less than a
>> /22), but better safe than sorry.
>> Verifying that there's a BGP announcement is trivial: go to any of the
>> hundreds of looking glasses. For the four-month rule, staff may want
>> to let it be practiced in the breach for now. That is, don't go out
>> and look unless someone complains. Writing software that actively
>> checks for it can be part of the address recovery strategy after
>> depletion.
>> Same deal with the route withdrawals: if slot consumption bugs the
>> ISPs, let them write a script which trolls for cheaters and then
>> complain.
>> To verify multihoming, I would suggest asking the registrant to
>> provide a letter of service from two ISPs in which they indicate that
>> they're under contract to announce routes for AS XXX.
>> To verify $8k, you might ask for a month's bills and check that 12
>> months worth adds up to $8k.
>> There's a respectable chance that folks requesting a /23 or larger
>> will continue to grow. It would be nice if ARIN staff made reasonable
>> efforts to reserve adjacent space for a year or so they may be able to
>> get the next larger size without having to renumber. With the scarcity
>> of IPv4 addresses this won't always be possible, but it would be good
>> to do as a "best efforts" kind of thing. .
>> 9. Timetable for implementation: immediate
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