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Solutions for IPv4 address exhaustion

Eurescom study P1952                                                                           

Pierre_LÚvis

Pierre LÚvis
Orange Labs
pierre.levis@orange-ftgroup.com

By the end of 2012, there will be no more public IPv4 addresses left to allocate to Internet Service Providers (ISPs). They will be left with an address pool that cannot be increased anymore. Immediate action is required by all stakeholders in order to mitigate and survive the consequences of IPv4 address exhaustion. Eurescom study P1952 explored how ISPs could tackle the problem in the short term. 

The principal solution for the shortage of IPv4 addresses is IPv6, which provides a much larger address space using 128 bits instead of 32 bits. However, at the exhaustion date, many customers and services will not yet have migrated to IPv6 and will only be accessible via IPv4. Therefore, deploying IPv6 is not sufficient to cope with the IPv4 address shortage in the short term. 

Facing the IPv4 shortage

There are three main components to solving the problem of IPv4 address shortage, all of which must be carried out in parallel. 

The first is the wide deployment of IPv6. IPv6 was created specifically to solve the problem of IP address depletion, and is the only long-term solution. 

The second is better utilisation of the existing IPv4 address space. For an ISP this may include network renumbering or restructuring, using private IP addresses or IPv6 addresses internally, using centralised address pools to raise efficiency, or re-assignment of delegated but unused IPv4 addresses (time-multiplexing of public IPv4 addresses). 

The third is the implementation of address sharing mechanisms. So far, the practice has been to give a unique IPv4 public address to each customer. In this context, the public addresses that can be seen in any Internet packets always refer to a unique customer. To cope with the IPv4 address exhaustion, this practice is no longer affordable. ISPs should allocate the same IPv4 public address to several customers at the same time. In this new context, a public IPv4 address seen in an Internet packet can refer to several customers. P1952 considers three main IPv4 address sharing solutions: NAT444 (Network Address Translation), DS-lite (Dual Stack-lite), and A+P (Address+Port).

IPv4 address allocation strategy

ISPs will have to consider the availability of addresses and should decide to whom they allocate shared addresses and to whom they allocate unique public addresses.

This choice will depend on several parameters such as:

  • Shared address eligibility (it may not be possible to provide a shared address to all customers).

  • Multiplicative factor (how many customers for the same address).

  • Service differentiation (e.g. “Premium service” with unique IPv4 address vs. “Standard service” with shared IPv4 address). 

ISP high level requirements to IPv4 address exhaustion solutions

All of the approaches to cope with the IPv4 address shortage introduce certain burdens and costs to the ISP. The following high-level requirements have been defined in order to help the ISPs with their decision process. The chosen solution for the IPv4 address space exhaustion has to:

  • Address the individual ISPs specific IPv4 address exhaustion problem.

  • Ensure business flexibility and future-readiness.

  • Provide transparency to the customer.

  • Be simple to operate and provide.

  • Be incrementally deployable. 

Conclusion

The IPv4 public address exhaustion is one of the main challenges the Internet is currently confronted with. ISPs should deploy address sharing solutions to maintain connectivity to the IPv4 Internet after the IPv4 addresses are exhausted. The important message to keep in mind is that IPv6 is the only solution which truly solves the IPv4 address exhaustion problem, and should be deployed as widely and as soon as possible.  

Further information on Eurescom study P1952 is available at www.eurescom.eu/Public/Projects/P1900-series/P1952

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