PI vs PA Address Space
Daniel Karrenberg Daniel.Karrenberg at ripe.net
Wed May 17 13:00:00 CEST 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.
Daniel
PI vs PA Address Space
Daniel Karrenberg
______________________________________________________
Provider Independent
vs
Provider Aggregatable
Address Space
Daniel Karrenberg
RIPE NCC
Version 1
Scope
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++.
Introduction
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
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PI vs PA Address Space
Daniel Karrenberg
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each end-site's individual routes would need to be
propagated throughout the whole interdomain routing
system.
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-
tem.
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.
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Daniel Karrenberg
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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
providers.
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-
sensus.
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-
cient.
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.
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PI vs PA Address Space
Daniel Karrenberg
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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
warning:
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-
way/firewall.
IRs will give those requesting PI space the following
warning:
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.
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Regional IRs
Regional IRs will introduce an address space type
(PA/PI) attribute in their assignment/allocation
databases.
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
space.
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
appropriate.
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ISPs
It is recommended that ISPs clearly specify present
and future differences in their service offerings
w.r.t. usage of PI vs PA addresses.
Availability
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>
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