[arin-ppml] Rationale for /22
joelja at bogus.com
Tue Jul 28 04:43:41 EDT 2009
Bill Darte wrote:
> Every effort to lower minimum allocations throughout the years has met
> with resistance. Each successful policy managed a 'bit at a time' to
> ensure 'nothing bad happened'....
Realistically is it in the interest of a prospective multihomer to a
recieve a prefix that's likely longer than the one they already use?
How quickly does one chew up /32s /30 /28s in the process of multihoming
the internet facing infrastructure in a smple-multihomed network?
> In recent years, there have been few calls for a further lengthening and
> those that emerged gained little support.
> Proposals are always welcome...
> Bill Darte
> ARIN AC
>> -----Original Message-----
>> From: arin-ppml-bounces at arin.net
>> [mailto:arin-ppml-bounces at arin.net] On Behalf Of William Herrin
>> Sent: Monday, July 27, 2009 11:04 AM
>> To: ARIN PPML
>> Subject: [arin-ppml] Rationale for /22
>> Question for y'all:
>> What is the rationale behind a /22 minimum size for
>> multihomed organizations? Why not a /24?
>> The reason behind /20 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 do we restrict ARIN
>> assignments to folks who can write papers which justify a /22?
>> Excluding conspiracy theories (the big bad ISPs want lock in)
>> I'd like to hear ideas, answers and even recollections from
>> folks who were there when the size was set as to why we
>> should prefer /22 as the minimum multihomed size assignable by ARIN.
>> Bill Herrin
>> William D. Herrin ................ herrin at dirtside.com bill at herrin.us
>> 3005 Crane Dr. ...................... Web:
>> <http://bill.herrin.us/> Falls Church, VA 22042-3004
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