2.8.10 Sharing of an IPv4 Address (shara)

NOTE: This charter is a snapshot of the 74th IETF Meeting in San Francisco, CA USA. It may now be out-of-date.

Last Modified: 2009-03-04


Marcelo Bagnulo <marcelo@it.uc3m.es>

Transport Area Director(s):

Magnus Westerlund <magnus.westerlund@ericsson.com>
Lars Eggert <lars.eggert@nokia.com>

Transport Area Advisor:

Magnus Westerlund <magnus.westerlund@ericsson.com>

Mailing Lists:

General Discussion:
To Subscribe:

Description of Working Group:

In the current Internet, it is fairly common for ISPs to provision their
subscribers with a single public IPv4 address and for those subscribers
to use NAT technology to allow multiple machines in their networks to
access the Internet. This setup essentially requires one public IPv4
address per subscriber. As the IPv4 free address pool becomes depleted,
it seems likely that  ISPs will not have enough public IPv4 addresses to
assign one address per subscriber. When that happens, multiple
subscriber networks will have to share a single public IPv4 address.
Multiple approaches have been proposed in order to implement the sharing
of public IPv4 addresses, as described in section 2.1 of

The goal of this BOF is to discuss and gain understanding of a
particular family of solutions, the so called distributed-NAT approaches
described in section 2.1.2 of draft-arkko-townsley-coexistence-00. This
family of solutions, essentially assigns a public IP address and a port
range to each subscriber and relies on some form of port range routing
capability within the ISP network. The result is that each subscriber
still obtains at least a part of a public IP address and retains some of
the capabilities of the current configuration.

During the BOF we intend to discuss the following items:
- Problem characterization: We need to understand what is exactly the
problem, what are the different scenarios that are affected by the IPv4
address space depletion and what are the possible approaches to address
the problem. In addition, we need to identify the different relevant
aspects of the problem and solution space that need to be taken into
account during the discussion of the solution space.
- Motivation for SHARA: Discuss the benefits and potential issues with a
distributed NAT approach.
- Distributed NAT approaches: Explore the solution space for distributed
NATs and the implications of the relevant aspects previously identified.
- Interaction with other efforts. There are a significant number of
efforts in related areas, such as the work being done in the BEHAVE WG
and the SOFTWIRES WG. It is then relevant to understand how the proposed
mechanisms interact with these.
- Implication for the deployment of IPv6. Any mechanism that aims to
extend the lifetime of IPv4 can potentially delay IPv6 deployment. An
analysis of the impact of the adoption of these techniques is needed.

This is non-wg forming BOF and the goal is to provide input material to
the community in general and the IESG in particular for them to scope
out what gaps still need to be addressed in chartered WG items in other WGs.

Goals and Milestones:

No Current Internet-Drafts

No Request For Comments

Meeting Minutes


Issues with address sharing approaches
SHARA Use cases
Benefits of NAT avoidance
Security Implications
What are we missing?
Implications of SHARA on Operations & Mgmt
Shara solutions space