Network Working Group K. Naito Internet-Draft A. Matsumoto Intended status: Informational NTT Expires: January 10, 2013 July 9, 2012 NAT Port Overlapping draft-naito-nat-port-overlapping-00 Abstract When network address translation (NAT) is used in an address resource restricted environment, or when a lot of users are located under a NAT device, IP addresses and port resources may be eaten up, and this affects user experiences very negatively. This situation can be greatly mitigated by tweaking mapping behavior and session timer handling in NAT functions. This document proposes extension for optimizing NAT IP address and port resources in address resource restricted environments. The extension enables simultaneous use of a NAT external port for different transport sessions. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on January 10, 2013. Copyright Notice Copyright (c) 2012 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect Naito & Matsumoto Expires January 10, 2013 [Page 1] Internet-Draft NAT Port Overlapping July 2012 to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English. 1. Introduction After IPv4 addresses run out, IPv4 address resources will be further restricted site-by-site. If global IPv4 address are shared between several clients, assignable port resources at each client will be limited. NAT is a tool that is widely used to deal with this IPv4 address shortage problem. However, the demand for resources to provide Internet access to users and devices will continue to increase. IPv6 is a fundamental solution to this problem, but the deployment of IPv6 will take time. In some cases, e.g. browsing a dynamic web page for a map service, a lot of sessions are used by the browser, and a number of ports are eaten up in a short time. What is worse is that when a NAT is between a PC and a server, TIME_WAIT state of each TCP connection is kept for certain period, typically for four minutes, which consumes port resources. Therefore, new connections cannot be established. This problem is caused or worsened by the following behavior. In a lot of NAT implementations, a port that is available in NAT is allocated for a transport session.That is, a NAT does not use a port for multiple sessions simultaneously. We propose mechanisms to change the above behavior that make it possible to save addresses and ports resources. Naito & Matsumoto Expires January 10, 2013 [Page 2] Internet-Draft NAT Port Overlapping July 2012 2. NAT resource optimizing extension proposal 2.1. Apply Port Overlapping mechanism If destination addresses and ports are different at the outgoing sessions started by local clients, NAT MAY assign the same external port as the source ports at the sessions. Port overlapping mechanism manages mappings between external packets and internal packets by looking at and storing the 5-tuple (protocol, source address, source port, destination address, destination port) of them. Thus, enables concurrent use of single port for multiple transport sessions, which enables NAT to work correctly in IP address resource limited network. Discussions: RFC4787 [RFC4787] and RFC5382 [RFC5382] requires "endpoint- independent mapping" at NAT, and port overlapping NAT cannot meet therequirement. This mechanism can degrade the transparency of NAT in that its mapping mechanism is endpoint-dependent and makes NAT traversal harder. However, if a NAT adopts endpoint-independent mapping together with endpoint-dependent filtering, then the actual behavior of the NAT will be the same as port overlapping NAT. It should also be noted that a lot of existing NAT devices adopted this port overlapping mechanism. 3. Security Considerations Security issues are not discussed in this memo. 4. Normative References [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC 793, September 1981. [RFC4787] Audet, F. and C. Jennings, "Network Address Translation (NAT) Behavioral Requirements for Unicast UDP", BCP 127, RFC 4787, January 2007. [RFC5382] Guha, S., Biswas, K., Ford, B., Sivakumar, S., and P. Srisuresh, "NAT Behavioral Requirements for TCP", BCP 142, RFC 5382, October 2008. Naito & Matsumoto Expires January 10, 2013 [Page 3] Internet-Draft NAT Port Overlapping July 2012 Authors' Addresses Kengo Naito NTT NT Lab 3-9-11 Midori-Cho Musashino-shi, Tokyo 180-8585 Japan Phone: +81 422 59 4949 Email: naito.kengo@lab.ntt.co.jp Arifumi Matsumoto NTT NT Lab 3-9-11 Midori-Cho Musashino-shi, Tokyo 180-8585 Japan Phone: +81 422 59 3334 Email: arifumi@nttv6.net Naito & Matsumoto Expires January 10, 2013 [Page 4]