Network Working Group L. Daigle Internet-Draft Editor Expires: July 10, 2002 Internet Architecture Board IAB January 9, 2002 IAB Considerations for UNilateral Self-Address Fixing (UNSAF) draft-iab-unsaf-considerations-00.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on July 10, 2002. Copyright Notice Copyright (C) The Internet Society (2002). All Rights Reserved. Abstract In order to alleviate the fundamental problem with current NA[P]T middleboxes altering the relationship between the apparent location and true identity of endpoints, various proposals have been made for "UNilateral Self-Address Fixing (UNSAF)" processes. These are processes whereby some originating process attempts to determine or fix the address (and port) by which it is known -- e.g., to be able to use address data in the protocol exchange, or to advertise a public address from which it will receive connections. This document outlines the reasons for which these proposals can be Internet Architecture Board Expires July 10, 2002 [Page 1] Internet-Draft draft-iab-unsaf-considerations-00 January 2002 considered at best as short term fixes to specific problems, and the specific issues to be carefully evaluated before creating an UNSAF proposal. 1. Introduction As predicted some years ago, the fundamental problem with current NA[P]T middleboxes is that they alter the relationship between the apparent location and true identity of endpoints. For some purposes, endpoints need to know their own apparent location, or fix a public address from which they will receive packets. "UNilateral Self- Address Fixing (UNSAF)" is a process whereby some originating process attempts to determine or fix the address (and port) by which it is known -- e.g., to be able to use address data in the protocol exchange, or to advertise a public address from which it will receive connections. There are only heuristics and workarounds to attempt to achieve this effect; there is no 100% solution. Use of these workarounds MUST be considered transitional in IETF protocols; a better architectural solution is being sought. The explicit intention is to deprecate any such workarounds when sound technical approaches are available. 2. Architectural Considerations for UNSAF Systems Any users of these workarounds should be aware that specific technical issues that impede the creation of a general solution include: o there *is* no unique "outside" to a NAT -- it may be impossible to tell where the target UNSAF partner is with respect to the source; how does a client find an appropriate server to reflect its address? o specifically because it is impossible to tell where "outside" or "public" is, an address can only be determined relative to one specific point in the network. If the UNSAF partner that reflected a client's address is in a different NAT-masked subnet from some other service X that the client wishes to use, there is _no_ guarantee that the client's "perceived" address from the UNSAF partner would be the same as the address viewed from the perspective of X. o absent "middlebox communication (midcom)" there is no usable way to let incoming communications make their way through a firewall under proper supervision: that is, respecting the firewall policies and as opposed to circumventing security mechanisms. Internet Architecture Board Expires July 10, 2002 [Page 2] Internet-Draft draft-iab-unsaf-considerations-00 January 2002 o the proposed "ping"-like services create stateful conditions; there is no guarantee that the state will remain consistent for the duration of the communication. o since the reflecting service is not integrated with the middlebox, it does not really know what the middlebox thinks it is doing and can only guess in an attempt to use past behavior as a predictor of future behavior. o the communication exchange is made more "brittle" by the introduction of other servers (UNSAF partners) that need to be reachable in order for the communication to succeed -- more boxes that are "fate sharing" in the communication. Work-arounds may mitigate some of these problems through tight scoping of applicability and specific fixes. For example, o rather than finding the address from "the" outside of the NAT, the applicability of the approach may be limited to finding the "self- address" from a specific service, for use exclusively with that service; o limiting the scope to outbound requests for service (or service initiation). By distinguishing these approaches as short term fixes, the IAB believes the following considerations must be explicitly addressed in any proposal: o Precise definition of a specific, limited-scope problem that is to be solved with the UNSAF proposal. A short term fix should not be generalized to solve other problems; this is why "short term fixes usually aren't". o Description of an exit strategy/transition plan. The better short term fixes are the ones that will naturally see less and less use as the appropriate technology is deployed. o Discussion of specific issues that may render systems more "brittle". For example, approaches that involve using data at multiple network layers create more dependencies, increase debugging challenges, and make it harder to transition. o Identify requirements for longer term, sound technical solutions - - contribute to the process of finding the right longer term solution. Internet Architecture Board Expires July 10, 2002 [Page 3] Internet-Draft draft-iab-unsaf-considerations-00 January 2002 3. Security Considerations As a general class of workarounds, as noted above UNSAF proposals may introduce security holes because, absent "middlebox communication (midcom)", there is no usable way to let incoming communications make their way through a firewall under proper supervision: respecting the firewall policies as opposed to circumventing security mechanisms. Authors' Addresses Leslie Daigle Editor Internet Architecture Board IAB EMail: iab@iab.org Appendix A. IAB Members at the time of this writing Harald Alvestrand Ran Atkinson Rob Austein Fred Baker Brian Carpenter Steve Bellovin Jon Crowcroft Leslie Daigle Steve Deering Sally Floyd Geoff Huston John Klensin Henning Schulzrinne Internet Architecture Board Expires July 10, 2002 [Page 4] Internet-Draft draft-iab-unsaf-considerations-00 January 2002 Full Copyright Statement Copyright (C) The Internet Society (2002). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. 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