[arin-ppml] Multihomed Microallocations
ARIN received the following policy proposal and is posting it to the
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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
> 18.104.22.168 The requesting organization must hold exactly one AS number
> and must already announce IPv4 addresses to the Internet via BGP using
> its AS number.
> 22.214.171.124. The requesting organization must announce IPv4 addresses to
> the Internet via at least two distinct Internet vendors.
> 126.96.36.199. The requesting organization must spend at least $8000/year on
> the Internet services in 188.8.131.52.
> 184.108.40.206. 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.
> 220.127.116.11. 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
> 18.104.22.168. 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.
> 22.214.171.124. 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.
> 126.96.36.199. 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.
> 188.8.131.52. 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
> 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?
> 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
> 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
> 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
> * 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 184.108.40.206 come from?
> A. Most likely from one of the ISPs as described in NRPM section
> 220.127.116.11. 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 18.104.22.168
> 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
> 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 22.214.171.124. It does impact end user
> assignments under NRPM section 126.96.36.199. 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
> Same deal with the route withdrawals: if slot consumption bugs the
> ISPs, let them write a script which trolls for cheaters and then
> 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