Internet DRAFT - draft-naito-nat-port-overlapping
draft-naito-nat-port-overlapping
Network Working Group K. Naito
Internet-Draft A. Matsumoto
Intended status: Informational NTT
Expires: January 18, 2013 July 17, 2012
NAT Port Overlapping
draft-naito-nat-port-overlapping-01
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 18, 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 18, 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 18, 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 the
requirement. 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(e.g., SEIL,
FITELnet Series) adopted this port overlapping mechanism. The
netfilter, which is a popular packet filtering mechanism for Linux,
also adopts port overlapping behavior.
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 18, 2013 [Page 3]
Internet-Draft NAT Port Overlapping July 2012
Appendix A. Revision History
'draft-naito-nat-resource-optimizing-extension-01' was divided into
two drafts after IETF83 meeting.
'draft-naito-nat-resource-optimizing-extension-01' containes two
mechanisms. One mechanism, port overlapping is written in this
draft, and the other is written in
'draft-naito-nat-time-wait-reduction-01'.
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 18, 2013 [Page 4]
