Network Working Group P. Levis, Ed.
Internet-Draft M. Boucadair
Intended status: Informational JL. Grimault
Expires: August 1, 2009 A. Villefranque
France Telecom
January 28, 2009
IPv4 Shortage Framework
draft-levis-behave-ipv4-shortage-framework-00.txt
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Abstract
This document analyses the main issues related to IPv4 Internet
access in the context of public IPv4 address exhaustion. It would be
valuable to assess each IPv4 address shortage solution with all these
issues, to check to what degree they are concerned, how they handle
each issue, and to what extent they resolve the pending problems.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Shared IPv4 Addresses . . . . . . . . . . . . . . . . . . . . 4
3. Address Space Multiplicative Factor . . . . . . . . . . . . . 5
4. Service Management . . . . . . . . . . . . . . . . . . . . . . 5
5. IPv6 Migration and IPv4-IPv6 Coexistence . . . . . . . . . . . 6
6. Solution-Level Issues . . . . . . . . . . . . . . . . . . . . 7
6.1. Network Addressing Capability . . . . . . . . . . . . . . 7
6.2. Number of Current Sessions per Customer . . . . . . . . . 7
6.3. Scarcity of Private Addressing . . . . . . . . . . . . . . 8
6.4. Impact on Information System . . . . . . . . . . . . . . . 8
6.5. Port Related Entries in the ISP Equipment . . . . . . . . 9
6.6. Legal Duties . . . . . . . . . . . . . . . . . . . . . . . 9
6.6.1. Traceability . . . . . . . . . . . . . . . . . . . . . 9
6.6.2. Interception . . . . . . . . . . . . . . . . . . . . . 9
6.7. Flow Discrimination . . . . . . . . . . . . . . . . . . . 9
6.8. Introduction of Single Point of Failure (Robustness) . . . 10
6.9. Impact on Intra-Domain and Inter-Domain Routing . . . . . 10
6.10. Fragmentation . . . . . . . . . . . . . . . . . . . . . . 10
6.11. Impact on Services . . . . . . . . . . . . . . . . . . . . 10
6.12. Impact on CPE . . . . . . . . . . . . . . . . . . . . . . 11
6.13. Support of Multicast . . . . . . . . . . . . . . . . . . . 12
6.14. Scalability . . . . . . . . . . . . . . . . . . . . . . . 12
6.15. Security . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.15.1. Port Randomization . . . . . . . . . . . . . . . . . . 12
6.15.2. Duplicate Effects . . . . . . . . . . . . . . . . . . 12
6.16. Management Tools . . . . . . . . . . . . . . . . . . . . . 13
6.17. Solution manageability . . . . . . . . . . . . . . . . . . 13
6.18. End-Users Facilities . . . . . . . . . . . . . . . . . . . 13
6.19. Service Access Discrimination . . . . . . . . . . . . . . 13
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
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8. Security Considerations . . . . . . . . . . . . . . . . . . . 14
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
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1. Introduction
Taking into consideration the IPv4 public address pool currently
available at the Internet Assigned Numbers Authority (IANA), it is
expected that the Regional Internet Registries (RIRs) will have no
more public IPv4 addresses to allocate in the short term. At the
time of writing, this anticipated date is mid-2012. See the IPv4
Address Report website www.potaroo.net/tools/ipv4/index.html for a
thorough analysis of this issue, and an updated prediction.
At the exhaustion date, ISPs will wind up with public address pools
that cannot grow. They will have to make do with what they have
currently got. They will enter an IPv4 address shortage management
phase. It will not be possible to provide each customer with a
unique public IPv4 address. On the other hand, offering only an
access to the IPv6 Internet won't be satisfactory for the customers
because a lot of services will remain IPv4-only accessible, and this
is for long period (a full IPv6 world requires universal agreement
which is hard to achieve).
This document analyses the main issues related to IPv4 Internet
access in the context of public IPv4 address exhaustion. The IPv4
Internet access from an IPv6 stack, and the IPv6 Internet access
whatever the means, are out of the scope of this memo.
2. Shared IPv4 Addresses
So far, the current practice has been to give a unique IPv4 public
address to each customer. A customer, then, can possibly share her
address among several hosts behind her Customer Premises Equipment
(CPE). In this context, the addresses that can be seen in any IP
packets always refer to a unique customer. To cope with the IPv4
address exhaustion, this kind of practices is no more affordable.
Therefore ISPs are bound to allocate the same IPv4 public address to
several customers at the same time.
All solutions claiming to solve the IPv4 address exhaustion (simply
referred to as solutions in the remaining part of this memo) are
based on shared addresses. In this new context, an IPv4 address seen
in an IP packet can refer to several customers. The port information
must be considered as well, in order to be able to unambiguously
identify the customer pointed by that shared address. In particular,
the port information along with the address information, must
eventually be taken into account by the routing infrastructure in
order to correctly reach the intended destination.
All IPv4 address shortage mechanisms extend the address space in
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adding port information. They differ on the way they manage the port
value.
3. Address Space Multiplicative Factor
The purpose of sharing IPv4 addresses is to potentially increase the
addressing space. A key parameter is the factor by which ISPs want
or need to multiply their IPv4 public address space; and the
consequence is the number of customers sharing the same public IPv4
address.
The intention is not to replace IPv6. However, we should be very
careful; whatever the network model deployed, applications and
business will run on top of it. The fact that the IPv4 shortage
mechanisms will not postpone IPv6 deployment, heavily relies on
voluntarism.
It is expected that the IPv6 communications will take an increasing
part during the next years to come, at the expense of the IPv4
communications. We should reach a safety point in the future, where
the number of IPv4 public addresses, in use at the same time, begins
decreasing. From an ISP point of view, the multiplicative factor
must be enough to survive until this occurs for its own customers.
Most likely a one digit factor (less than 10) should be sufficient,
and it should not be relevant to go beyond. Whereas the potential is
huge, -if we allow to each customer (one IP address, 1000 ports) we
multiply by 64 the total IPv4 address space- trying to devise
solutions that can increase the IPv4 space by a significantly bigger
factor might be seen as an incentive to postpone again and again IPv6
deployment.
4. Service Management
At the time of IPv4 address exhaustion in the RIRs, ISPs will have to
manage public address pools that cannot grow (at least from the
RIRs). Concretely, they will have to decide to whom they allocate
shared addresses and to whom they allocate unique addresses, to the
extent of the availability of addresses. Many policies can be
envisaged, taking into account parameters such as: old vs. new
customers, user profile, access type, geographic considerations,
unique address as the privileged choice, shared address as the
privileged choice, etc.
An important issue is whether shared and unique addresses will
differently be charged.
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For the sake of safety and flexibility, ISPs should not drop their
public pool size under a minimum (safety number). They can adjust
the volume of IPv4 public addresses available playing on the balance
between shared and unique allocations.
o To increase the public IPv4 address pool: increase the number of
customers with shared address; increase the ratio of customers per
shared address.
o To decrease the public IPv4 address pool: decrease the number of
customers with shared address; decrease the ratio of customers per
shared address.
5. IPv6 Migration and IPv4-IPv6 Coexistence
Any IPv4 address shortage solution should make use, as much as
possible, of the IPv6 transport capabilities available, in order to
increase the IPv6 packets traffic and to move forward from an IPv4-
enabled ISP network towards an almost only IPv6-enabled ISP network.
If it is not the case, the risk is to delay IPv6 deployments, in
staying on a pure dual-stack attitude for ever, similar to the ships
in the night routing approach, where the protocols independently live
their own lives.
The IPv4 in IPv6 tunnels, and/or the translation NAT464 should be
favored. However, increasing the number of IPv6 packets does not
automatically mean IPv6 is being generalized, if the main purpose of
these packets is to carry IPv4 information. This is very similar to
what occurred with ATM, especially in European countries, where ATM
cells have heavily been used to convey IPv4 packets in the backhaul
networks, but have never been used for end-to-end communications.
If the percentage of end-to-end IPv6 traffic significantly increases,
so that the volume of IPv4 traffic begins decreasing, then the number
of IPv4 sessions will be decreasing. The smaller the number of
current sessions per customer is, the higher the number of customers
under the same IPv4 public address can be, and consequently, the
lower the number of IPv4 public addresses is needed. Hence, the
pressure on IPv4 address shortage would be relaxed, because one IPv4
public address would be able to serve more customers. However, this
effect will only occur for customers who have both an IPv6 access and
a shared IPv4 access. This would advocate the strategy to
systematically bound a shared IPv4 access to any IPv6 access.
Furthermore, a significant number of public IPv4 addresses will be
needed in the interconnection between IPv4 and IPv6 realms, for the
sake of global reachability.
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6. Solution-Level Issues
All IPv4 address shortage solutions will be confronted to the
hereafter listed issues. It is valuable to assess each solution with
all these issues, to check to what degree they are concerned, how
they handle each issue, and to what extent they resolve the pending
problems.
6.1. Network Addressing Capability
The network addressing capability is the level of flexibility the
network has to configure customers' devices, either with a unique
address, or with a shared IPv4 address. It can be assessed through
the following considerations:
o Is it possible to configure any customer's device with a shared
address, regardless his location and his history?
o Is it possible to configure any customer's device with a unique
public address, regardless his location and his history?
o Is it straightforward to switch, for any customer, from a shared
address to a unique public address, and vice versa?
What is considered here is not the policy decision to allocate a
unique or a shared address, but indeed the network capability to
enforce such address management schemes.
Any addressing scheme should be backward compatible with the current
practices. Means to convey IP connectivity (e.g. DHCP, PPP) should
be the same as the ones implemented by service providers. Additional
facilities and tools to ease the shared IPv4 address management
should be promoted.
6.2. Number of Current Sessions per Customer
In any kind of solutions, the number of current sessions per customer
has, de facto, to be limited in some way. Therefore, the number of
current sessions per customer is a limit to take into account in any
architectural dimensioning. The degree of fairness -balanced
distribution of sessions between customers-, should be assessed.
Means to prevent against traffic loss (due to the limitation in
number of sessions) should be evaluated and proposed. The importance
of this issue may be greatly reduced if the multiplicative factor is
very small (e.g. 4).
As for the current usage of ports, several hundreds per customer
seems current practice, although several thousands may be not unusual
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with some P2P applications (e.g. BitTorrent).
The impact of the dynamicity of the sessions should also be
considered, especially as far as performance is concerned.
6.3. Scarcity of Private Addressing
According to [RFC1918], IPv4 private addresses must be chosen in the
following ranges:
o 10/8
o 172.16/12
o 192.168/16
There is a potential of 2 at the power of (224 + 220 + 216)
addresses, or 17,891,328 addresses. Actually, private addresses are
not that abundant when deployments are concerned. Some ISPs already
use private addresses within their networks for specific usage such
as walled garden services, in a way they cannot reuse them for
another usage. As a consequence, the smallness of the IPv4 private
address pool available for the Internet service could force some ISPs
to use Virtual Private Networks (VPNs) such as [RFC4364] to allow
reusing the same private addresses several times with no routing
overlaps. This brings a lot of complexity in network configuration
and management.
It has been suggested to make the 240./4 block available for private
addressing [I-D.wilson-class-e]. This address block, formerly
designated as "Class E", is still noted as being reserved in the IANA
IPv4 address registry. If it were reassigned for private addressing
that would yield around 268 millions extra private addresses.
However, many current implementations of the TCP/IP protocol stack do
not allow the use of the 240./4 block. This is a severe blocking
point for a lot of existing devices: CPE, NAT or routers. This issue
will only be solved when the vendors' implementations accept the
(240./4) addresses.
Another suggestion [I-D.shirasaki-isp-shared-addr] is to reserve some
public blocks (typically three or four /8) only for internal usage.
So far, there has been no consensus upon this proposal.
6.4. Impact on Information System
The IPv4 address shortage solutions could add port information in the
Information System (IS) at different levels. For instance, the
possibility to give either a unique or a shared address, coupled or
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not with an IPv6 address, could yield several types of customers to
deal with in the IS: IPv4 unique only, IPv4 shared only, IPv4 unique
+ IPv6, IPv4 shared + IPv6, IPv6 only. The impact on the IS
platforms and IS applications should be evaluated and assessed.
6.5. Port Related Entries in the ISP Equipment
Additional data related to port information should be stored and
maintained by the ISP equipment. As an example, a set of entries
(e.g. session states, binding entries) are to be instantiated and
maintained. The logic instantiation (behavior and not necessarily
detailed algorithms) of these entries should be standardized to avoid
interoperability problems, and ease management tasks. Optimization
means for instantiating new entries should be investigated and
deployed if required. In addition, the amount of entries to be
maintained should not be too big.
6.6. Legal Duties
ISPs are legally required to give access to information related to
their users' communications on request of the authorities.
6.6.1. Traceability
Legal obligations require an ISP to provide the identity of a
customer upon request of the authorities. Because one public IPv4
address may be shared between several users, the knowledge of the
port number, along with the IP address, is mandatory to have a chance
to find the appropriate user. The ISP must be able to provide the
identity of a customer from the knowledge of the IPv4 public address
and the port number.
6.6.2. Interception
This process is proactive, a given group of communications is
replicated in real time towards a law enforcement agency. Typically,
the point of replication is the first IP hop in the ISP network. The
mechanism put in place must be completely transparent to the
customers, so that the targeted customer cannot be aware of the
interception.
6.7. Flow Discrimination
The ISP can offer walled garden services along with Internet
services. Typically, walled garden services packets are exchanged
between the customers and a Service Platform or a Service Gateway.
The ISP may want these flows not to traverse the IPv4 shortage
facilities put in place (for instance TV flows should bypass a
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Carrier Grade NAT). However, the best practice seems to rapidly
migrate these services from IPv4 to IPv6.
The activation of solutions to solve the IPv4 shortage problem should
not alter mechanisms to enforce QoS or traffic engineering within a
given domain. Examples of these mechanisms are: DiffServ, RSVP, etc.
6.8. Introduction of Single Point of Failure (Robustness)
The introduction of new nodes/functions, specifically where the port
information is managed, can create single points of failure. Any
IPv4 shortage solution should consider the opportunity to add
redundancy features in order to alleviate the impact on the
robustness of the IP connectivity service.
Additionally, load balancing and load sharing means should be
evaluated. The ability of the solution to allow hot swapping from a
machine to another, in minimizing the perturbations, should be
considered.
End-to-end performances (e.g. delay) experienced in the context of a
new addressing solution should be at least similar to the currently
experienced one. QoS should not be severely altered when new means
are activated to solve IPv4 address exhaustion.
6.9. Impact on Intra-Domain and Inter-Domain Routing
The introduction of port consideration to route packets to their
final destinations may have an impact on the current routing
infrastructure: on the architecture, the IGP and EGP configuration,
and the addressing configuration. The introduction of new nodes that
cannot be circumvent could also yield non optimized routes,
especially for communications between customers attached to the same
ISP realm.
6.10. Fragmentation
When a packet is fragmented, the port information (either UDP or TCP)
will only be present in the first fragment. The other fragments will
not bear the port information which is necessary to a correct
treatment up to the destination. Appropriate solutions should be
investigated if required by service providers.
6.11. Impact on Services
There is a potential danger for the following types of applications:
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o Applications that establish inbound communications
o Applications that carry address information in their payloads
o Applications that do not use any port (e.g. ICMP)
o Applications that assume the uniqueness of customers' addresses
o Applications that explicitly prohibit twice the same address to
access to a resource at the same time
Current applications already implement some mechanisms in order to
circumvent the presence of NATs (typically CPE NATs):
o ALGs
o Port Forwarding
o UPnP IGD
o NAT Traversal
It should be considered to what extent these mechanisms can still be
used with IPv4 shortage mechanisms put in place.
Impact on existing services:
o Will this service work as usual?
o Will this service work but with a degradation?
o What level of degradation?
o Will this service not work at all?
o What modifications are needed if any?
Impact on future services:
o What new constraints are to be taken into account to devise new
services?
6.12. Impact on CPE
IPv4 shortage mechanisms may require specific features in the CPEs.
Some CPEs are ISP branded. CPEs are particularly sensible devices by
their number and by the fact that they are often optimized for a well
defined set of treatments closely related to the ISP's services. The
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impact on existing CPE devices should be carefully evaluated, taking
into account: features needed, required modifications, availability.
This requirement is not specific to ISP branded CPEs. CPE behavior
should be particularly specified by any solution claiming to solve
the IPv4 address exhaustion problem.
6.13. Support of Multicast
It should be assessed if a customer with a shared address can receive
multicast packets and source multicast packets.
Particularly, impact on IGMP should be identified and solutions
proposed. Because of the presence of several end user devices with
the same IP address, membership to multicast groups should be
evaluated and enhancement should be proposed if required. Besides
the membership issues, building multicast trees may be impacted.
This impact should be assessed and alternatives proposed.
6.14. Scalability
Any claimed solution to solve the IPv4 address shortage should be
able to deliver the IP connectivity services to a large amount of
customers, this limit should be evaluated.
6.15. Security
6.15.1. Port Randomization
A kind of blind attacks that can be performed against TCP relies on
the attacker's ability to guess the five-tuple (Protocol, Source
Address, Destination Address, Source Port, Destination Port) that
identifies the transport protocol instance to be attacked. Document
[I-D.ietf-tsvwg-port-randomization] describes a number of methods for
the random selection of the client port number, such that the
possibility of an attacker guessing the exact value is reduced. With
shared IPv4 addresses, the port selection space is reduced.
Intuitively, assuming the port range is known, the smaller the port
range is, the more predictable the port choice is.
Any solution to solve IPv4 address shortage should specify how port
randomization is impacted and what alternative means to bypass the
issue are.
6.15.2. Duplicate Effects
Some types of attacks that have an impact on a targeted IPv4 public
address, could see their effects increased by the number of customers
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who share this address. For example, if a given address that has,
deliberately or not misbehaved, is consequently forbidden to access
some resources, the whole set of customers who share this address
will be impacted.
6.16. Management Tools
ISPs deploy a set of tools and applications for the management of
their infrastructure, especially for supervision purposes. Impact on
these tools should be evaluated and solutions proposed when required.
Particularly, means to assign IP connectivity information, means to
monitor the overall network, to assess the reachability of devices
should be specified. In this context, impact on ICMP should be
evaluated.
6.17. Solution manageability
The manageability of any new solution to be activated within service
providers realms should be evaluated and complexity avoided.
Particularly, required provisioning operations should be known and
not complex to enforce. The orchestration of required functions and
nodes should be specified.
6.18. End-Users Facilities
In the current deployments, end-users are used to configure their
CPEs in order to control the traffic entering/exiting to their home
LAN. Examples of these facilities are: port forwarding or firewall
rules. These facilities should be allowed in the context of IPv4
address exhaustion solutions. No major degradation compared to the
current practice should be perceived by end users. Functional
richness and quality of experience should be at the same level.
6.19. Service Access Discrimination
End-users should not be discriminated based on the assigned IP
address. The IP connectivity services should be the same for all
users. Particularly, accessing the added value services should be at
large extent not based on IP address. Applications developers are
encouraged to not embed "hard" IPv4 addresses in their software.
7. IANA Considerations
There are no IANA considerations.
Note to RFC Editor: this section may be removed on publication as an
RFC.
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8. Security Considerations
Security considerations are discussed in the Security section
9. References
[I-D.ietf-tsvwg-port-randomization]
Larsen, M. and F. Gont, "Port Randomization",
draft-ietf-tsvwg-port-randomization-02 (work in progress),
August 2008.
[I-D.shirasaki-isp-shared-addr]
Shirasaki, Y., Miyakawa, S., Nakagawa, A., Yamaguchi, J.,
and H. Ashida, "ISP Shared Address",
draft-shirasaki-isp-shared-addr-01 (work in progress),
October 2008.
[I-D.wilson-class-e]
Wilson, P., Michaelson, G., and G. Huston, "Redesignation
of 240/4 from "Future Use" to "Private Use"",
draft-wilson-class-e-02 (work in progress),
September 2008.
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, February 1996.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, February 2006.
Authors' Addresses
Pierre Levis (editor)
France Telecom
42 rue des Coutures
BP 6243
Caen Cedex 4 14066
France
Email: pierre.levis@orange-ftgroup.com
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Mohamed Boucadair
France Telecom
Email: mohamed.boucadair@orange-ftgroup.com
Jean-Luc Grimault
France Telecom
Email: jeanluc.grimault@orange-ftgroup.com
Alain Villefranque
France Telecom
Email: alain.villefranque@orange-ftgroup.com
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