IPv6 Site Renumbering (6renum)

Last modified: 2013-10-11


Operations and Management Area Advisor

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Description of Working Group:

As outlined in RFC 5887, renumbering, especially for medium to large sites and networks, is currently viewed as an expensive, painful, and error-prone process, avoided by network managers as much as possible.

As that RFC describes, there are triggers that mean some cases of renumbering are unavoidable, so it should be considered a given that a site may need partial or complete renumbering at some stage. It is thus important to implement and deploy techniques that facilitate simpler IPv6 site renumbering, so that as IPv6 becomes universally deployed, renumbering can be viewed as a more routine event. This includes consideration of how the initial assignment and subsequent management of address information is performed, as this will affect future renumbering operations.

If IPv6 site renumbering continues to be considered difficult, network managers will turn to PI addressing for IPv6 to attempt to minimise the need for future renumbering. However, widespread use of PI may create very serious BGP4 scaling problems. It is thus desirable to develop tools and practices that may make renumbering a simpler process to reduce demand for IPv6 PI space.

Renumbering, or partial renumbering, can be complicated in an enterprise site where a short prefix is divided into subnets with longer prefixes. Aggregation, synchronisation, coordination, etc., need to be carefully managed, and the use of manually inserted address literals minimised.

Other factors such as applications binding long-term to low level IP addresses may add constraints to what can be realistically achieved, but identifying and documenting such factors is a useful objective. In some scenarios, consideration may also need to be made for 'flag day' renumbering (in contrast to the procedure described in RFC4192).

The task of the 6RENUM working group is to document existing renumbering practices for enterprise site networks and to identify specific renumbering problems or 'gaps' in the context of partial or site-wide renumbering. Completion of these tasks should provide a basis for future work to identify and develop point solutions or system solutions to address those problems or to stimulate such development in other working groups as appropriate.

6RENUM is chartered to perform an analysis of IPv6 site renumbering. If the analysis leads to conclusions that are also applicable to IPv4 that will be an advantage, but it is not an objective of the WG to make its outputs more widely available than IPv6. Similarly the WG is targeting enterprise networks, but the analysis may also be applicable to SOHO or other (e.g. ad-hoc) scenarios.

It may be that for site renumbering to become more routine, a systematic address management approach will be required. By documenting current practices and undertaking a gap analysis, we should become better informed of the requirements of such an approach. Post-analysis rechartering may lead to further work in this area. RFC 4192, RFC 5887, and draft-jiang-ipv6-site-renum-guideline are starting points for this work.


The goals of the 6RENUM working group are:

  1. To undertake scenario descriptions, including documentation of current capability inventories and existing BCPs, for enterprise networks, including managed and unmanaged elements. These texts should contribute towards a gap analysis and provide an agreed basis for subsequent WG rechartering towards development of solutions (which may be more appropriate for other WGs to undertake) and improved practices. Operator input will be of high value for this text.
  2. To perform a gap analysis for renumbering practices, to identify generic issues for network design, network management, address management and renumbering operations. The methodology for the WG will be to begin building the enterprise scenario description while in parallel constructing an initial gap analysis drawing on existing work in (at least) RFC4192 and RFC5887. As the scenario text hardens, its contributions will be incorporated into the more detailed gap analysis, which can be published once the scenario text is completed. The deliverables are thus the scenario and gap analysis texts.

The following topics are out of scope for the working group:

  1. Renumbering avoidance; this can perhaps be considered by appropriate IRTF groups. As documented in RFC5887, renumbering cannot be completely avoided. The WG is limited to dealing with how to renumber when it is unavoidable.
  2. IPv4 renumbering. While many sites are likely to run dual-stack, IPv6 is the future and, especially given concerns over extensive use of IPv6 PI, the most appropriate place to focus effort.
  3. ISP renumbering; this is potentially the most complex renumbering case. However, more benefit can be achieved by focusing effort on site renumbering. The enterprise site analysis should include the ISP's role in the site's renumbering events.
  4. Neither SOHO nor manet networks are targeted by the WG. However, if outputs from the WG are applicable to those scenarios, that would be an advantage.

A recharter of the WG will be possible once the gap analysis and scenario description are completed and published. Such rechartering would identify more specific work items within the 6RENUM WG or appropriate protocol WGs, and may include a proposal for work on a systematic address management approach.

Goals and Milestones

Oct 2011
IPv6 enterprise site scenario draft ready for WG adoption
Nov 2011
Gap analysis document ready for WG adoption
Jun 2012
IPv6 enterprise site scenario draft ready for WGLC
Jul 2012
Gap analysis document ready for WGLC
Jul 2012
Static addressing gap analysis doc ready for WG adoption
Aug 2012
Static addressing gap analysis doc ready for WGLC

No Internet-Drafts

Request for Comments

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