PI vs PA Address Space

Daniel Karrenberg Daniel.Karrenberg at ripe.net
Wed May 17 11:00:00 UTC 1995

Dear colleagues,

below you find a contribution to the Provider Independent Address Space
debate. I have written it from the point of view of a regional registrar
taking into account public and private discussions with various people 
at the last IETF and the last RIPE meeting.

It spells out what I personally consider sensible and most importantly 
practicable, read: implementable. 

The intention is to focus the discussion on the issue and get consensus 
for the work on the details e.g. RFC1466bis, ripe-104++ ... .

Comments very welcome.
If you agree, tell me too.


                                                        PI vs PA Address Space

                                                             Daniel Karrenberg

                                  Provider Independent


                                 Provider Aggregatable

                                     Address Space

                                   Daniel Karrenberg
                                        RIPE NCC

                                       Version 1


                        This  memo is a contribution to the ongoing discussion
                        about Provider Independent (portable)  address  space.
                        It is intended to build consensus on practical address
                        assignment policies to be  (re)defined  in  RFC1466bis
                        and regional policies, most concretely ripe-104++.


                        One  can  currently  distinguish two kinds of globally
                        unique, unicast IPv4 addresses:  provider  independent
                        (PI) and provider aggregatable (PA) addresses.

                        There  are  also non globally unique e.g. private uni-
                        cast addresses as described in RFC1597 which are suit-
                        able  for  many  applications.  These  are outside the
                        scope  of this memo as are multicast addresses.

          Provider Aggregatable Address Space

                        With the introduction of classless interdomain routing
                        (CIDR)  [RFC1519]  in  the  Internet, address space is
                        typically assigned by  an  Internet  service  provider
                        (ISP) to a customer. The service provider assigns this
                        address space in such a way that  routing  information
                        for  many  customers  can be aggregated once it leaves
                        the provider's routing domain.  This keeps the  number
                        of  routes  in  the  interdomain  routing system at an
                        acceptable level. The number of aggregated  routes  is
                        much  lower  than  the  number that would be needed if
                        pispas.txt                                      Page 1
                                                        PI vs PA Address Space

                                                             Daniel Karrenberg

                        each  end-site's  individual  routes  would need to be
                        propagated throughout the  whole  interdomain  routing

                        After  a  customer  leaves  the  service  provider who
                        assigned the address space,  it  can  be  assigned  to
                        another  customer.  As a consequence the customer will
                        have to reconfigure all their  hosts  and  routers  if
                        they  continue  to  require  globally  unique  address
                        space.  This requires a clear, preferably contractual,
                        understanding  between  the assigning service provider
                        and the customer, that the assignment of  the  address
                        space ends when the provider no longer provides Inter-
                        net connectivity to the customer or soon thereafter.

                        The reason for this arrangement is  the  load  on  the
                        interdomain  routing system.  If the customer used the
                        address space assigned to and  aggregatable  by  their
                        previous  service  provider when connecting to another
                        service provider, their routing information could  not
                        be  aggregated  and  would have to be propagated sepa-
                        rately throughout the whole interdomain  routing  sys-

          Provider Independent Address Space

                        Contrary to PA address space, PI address space remains
                        assigned to its user as long as the criteria  for  the
                        original  assignment  are met independently of the use
                        of a particular provider's  services.   Frequently  PI
                        addresses  are  not  even assigned by providers but by
                        other Internet registries. The apparent  advantage  of
                        PI  address  space  is  that the user does not have to
                        reconfigure their hosts and routers if they decide  to
                        leave  a  particular  service  provider.   However, PI
                        addresses are expensive to route because no use can be
                        made  of aggregation. All early Internet address space
                        assignments were provider  independent.  Many  assign-
                        ments made by ISPs are also formally provider indepen-
                        dent because they lack the clear  prior  understanding
                        between  ISP and customer that the assignment will end
                        with the termination of the service.

          Current Issues

                        At the time of this writing there is  growing  concern
                        among  the  operators of major transit routing domains
                        in the Internet that the number of  individual  routes
                        and  their  associated  information  is growing faster
                        than the deployed routing technology will be  able  to
                        handle.  Parts  of  the interdomain routing system are
                        already operating at capacity.
                        pispas.txt                                      Page 2
                                                        PI vs PA Address Space

                                                             Daniel Karrenberg

                        It  has  been  argued  that  PI addresses will quickly
                        become be totally useless since the  Internet  routing
                        system will not be able to support them any longer.

                        Consequently  it  has been suggested that the regional
                        IRs should immediately stop allocating  and  assigning
                        PI  space  and  only  allocate  PA  space  to  service

                        The regional IRs cannot do  this  because  they  would
                        face  determining who is a service provider and who is
                        not as well as enforcing  minimum  sizes  for  address
                        allocations.  This  would  amount to nothing less than
                        the registries regulating Internet service  provision.
                        So  far no practical policies for these determinations
                        have been suggested let alone met with community  con-

          Recommended Policy

                        We therefore suggest that the Internet Registries con-
                        tinue to register both PA  and  PI  address  space  to
                        users until workable policies can be established.

                        IRs  will  clearly  warn users about the issues w.r.t.
                        their choice of a particular type  of  address  space.
                        IRs  will  promote the use of private (RFC1597) and PA
                        address space as much as possible. Assignment criteria
                        for  both kinds of address space will be exactly iden-
                        tical w.r.t. the amount of address space assigned, the
                        registration  requirements  etc..   This  also implies
                        that assigning PI space prefixes longer than  24  bits
                        is  perfectly acceptable if the request does not merit
                        24 bits of address space to be assigned.

                        It should be  clear  from  the  address  range  itself
                        whether the address concerned is PI or PA. Currently a
                        registration of the fact at /16 level is deemed suffi-

                        It  is  then  up  to  the  service providers to decide
                        whether they will route particular  prefixes  or  not.
                        The way this determination is made is beyond the scope
                        of this document, but we  expect  that  accepting  and
                        charging routing announcements based on whether or not
                        they can be aggregated is a distinct possibility.

                        We therefore urgently recommand that service providers
                        shall  inform  their current and prospective customers
                        as clearly as possible about the  issues  involved  in
                        using PI vs PA space with their service offerings.

                        pispas.txt                                      Page 3
                                                        PI vs PA Address Space

                                                             Daniel Karrenberg

          Detailed Recommendation

                        The remainder of this document spells out some of  the
                        details concerning the policy.

          All IRs

                        IRs  will give those requesting PA space the following

                             Assignment of this address space is valid as
                             long   as  the  criteria  for  the  original
                             assignment are still met and  only  for  the
                             duration  of  the  service agreement between
                             yourself and ISP  XXXX  who  will  have  the
                             right  to  re-assign  the  address  space to
                             another user upon termination of the  agree-
                             ment  or  an agreed period thereafter.  This
                             means that you will have to re-configure the
                             addresses   of   all  equipment  using  this
                             address space if  you  continue  to  require
                             global  uniqueness  of those addresses. Note
                             that some Internet services do  not  require
                             globally   unique   addresses   if  accessed
                             through a NAT  or  application  layer  gate-

                        IRs  will give those requesting PI space the following

                             Assignment of this address space is valid as
                             long   as  the  criteria  for  the  original
                             assignment are still met.  However,  assign-
                             ment  of  address  space does NOT imply that
                             this address space will be ROUTABLE  ON  ANY
                             PART  OF  THE  INTERNET. It is expected that
                             users will have to pay a premium for  actual
                             routing  of  PI  addresses  as opposed to PA
                             addresses.  It may eventually become  impos-
                             sible  to get relatively small amounts of PI
                             space routed on most of  the  Internet.   We
                             strongly suggest you contact any prospective
                             service provider for information  about  the
                             possibility  and  pricing  of  service  when
                             using PI addresses.

                        IRs will recommend that end-users use PA space as much
                        as possible.

                        pispas.txt                                      Page 4
                                                        PI vs PA Address Space

                                                             Daniel Karrenberg

          Regional IRs

                        Regional IRs will  introduce  an  address  space  type
                        (PA/PI)   attribute   in  their  assignment/allocation

                        Regional IRs will from now on register clearly whether
                        specific  /16 blocks contain only PI or only PA space.

                        Regional IRS will make sure local IRs  understand  the
                        difference  between  address  space  types and support
                        local IRs in this issue.

                        Regional IRs will work to make both types  of  address
                        space available to users.

          Local IRs

                        Local  IRs may decide which kind they of address space
                        they will register: PA, PI or both.

                        Local IRs will refer requesters to an  appropriate  IR
                        for the address space type not offered by the IR.  ISP
                        IRs not offering PI space shall support  the  IR  that
                        does  concerning assignments to their customers w.r.t.
                        formatting request, furnishing background information,
                        charging etc..

                        Local  IRs  which do not normally assign large amounts
                        of a particular type of address space need not hold an
                        allocation  of  that type of  address space.  They can
                        get it as needed from their parent  IR.          Local
                        IRs  will  make  it  clear  to  the user which type of
                        address space is assigned. Clear contractual  arrange-
                        ments  are recommended in general and mandatory for PA

                        IRs have assigned address space in the past  which  is
                        de-facto  aggregated  but not formally PA type because
                        there are no clear contractual arrangements about ter-
                        mination  of the assignment. IRs will work to make the
                        contractual arrangements for these addresses after the
                        fact as much as possible.

                        Local  IRs  will  clearly  mark all new assignments of
                        address  space  in  the  assignment  database(s)  with
                        either PA or PI as appropriate.

                        Local  IRs  will  work to mark all past assignments in
                        the assignment database(s) with either  PA  or  PI  as
                        pispas.txt                                      Page 5
                                                        PI vs PA Address Space

                                                             Daniel Karrenberg


                        It is recommended that ISPs  clearly  specify  present
                        and  future  differences  in  their  service offerings
                        w.r.t. usage of PI vs PA addresses.


                        ftp://ftp.ripe.net/ripe/drafts/pispas.txt (ASCII)
                        ftp://ftp.ripe.net/ripe/drafts/pispas.ps (PostScript).

          Author's Addresses

                        Daniel Karrenberg
                        RIPE NCC
                        Kruislaan 409
                        NL-1098 SJ  Amsterdam

                        +31 20 592 5065

                        <Daniel.Karrenberg at ripe.net>

                        pispas.txt                                      Page 6

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