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(See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (March 26, 2012) is 4415 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- ** Obsolete normative reference: RFC 793 (Obsoleted by RFC 9293) ** Obsolete normative reference: RFC 1323 (Obsoleted by RFC 7323) Summary: 4 errors (**), 0 flaws (~~), 2 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group K. Naito 3 Internet-Draft A. Matsumoto 4 Intended status: Informational NTT 5 Expires: September 27, 2012 March 26, 2012 7 NAT resource optimizing extension 8 draft-naito-nat-resource-optimizing-extension-01 10 Abstract 12 When network address translation (NAT) is used in an address resource 13 restricted environment, or when a lot of users are located under a 14 NAT device, IP addresses and port resources may be eaten up, and this 15 affects user experiences very negatively. This situation can be 16 greatly mitigated by tweaking mapping behavior and session timer 17 handling in NAT functions. This document proposes two extensions for 18 optimizing NAT IP address and port resources in address resource 19 restricted environments. One extension enables simultaneous use of a 20 NAT external port for different transport sessions, and the other 21 makes use of a TCP timestamp for TIME_WAIT assassination. 23 Status of this Memo 25 This Internet-Draft is submitted in full conformance with the 26 provisions of BCP 78 and BCP 79. 28 Internet-Drafts are working documents of the Internet Engineering 29 Task Force (IETF). Note that other groups may also distribute 30 working documents as Internet-Drafts. The list of current Internet- 31 Drafts is at http://datatracker.ietf.org/drafts/current/. 33 Internet-Drafts are draft documents valid for a maximum of six months 34 and may be updated, replaced, or obsoleted by other documents at any 35 time. It is inappropriate to use Internet-Drafts as reference 36 material or to cite them other than as "work in progress." 38 This Internet-Draft will expire on September 27, 2012. 40 Copyright Notice 42 Copyright (c) 2012 IETF Trust and the persons identified as the 43 document authors. All rights reserved. 45 This document is subject to BCP 78 and the IETF Trust's Legal 46 Provisions Relating to IETF Documents 47 (http://trustee.ietf.org/license-info) in effect on the date of 48 publication of this document. Please review these documents 49 carefully, as they describe your rights and restrictions with respect 50 to this document. Code Components extracted from this document must 51 include Simplified BSD License text as described in Section 4.e of 52 the Trust Legal Provisions and are provided without warranty as 53 described in the Simplified BSD License. 55 This document may contain material from IETF Documents or IETF 56 Contributions published or made publicly available before November 57 10, 2008. The person(s) controlling the copyright in some of this 58 material may not have granted the IETF Trust the right to allow 59 modifications of such material outside the IETF Standards Process. 60 Without obtaining an adequate license from the person(s) controlling 61 the copyright in such materials, this document may not be modified 62 outside the IETF Standards Process, and derivative works of it may 63 not be created outside the IETF Standards Process, except to format 64 it for publication as an RFC or to translate it into languages other 65 than English. 67 1. Introduction 69 After IPv4 addresses run out, IPv4 address resources will be further 70 restricted site-by-site. If global IPv4 address are shared between 71 several clients, assignable port resources at each client will be 72 limited. 74 NAT is a tool that is widely used to deal with this IPv4 address 75 shortage problem. However, the demand for resources to provide 76 Internet access to users and devices will continue to increase.IPv6 77 is a fundamental solution to this problem, but the deployment of IPv6 78 will take time. 80 In some cases, e.g. browsing a dynamic web page for a map service, a 81 lot of sessions are used by the browser, and a number of ports are 82 eaten up in a short time. What is worse is that when a NAT is 83 between a PC and a server, TIME_WAIT state of each TCP connection is 84 kept for certain period, typically for four minutes, which consumes 85 port resources. Therefore, new connections cannot be established. 87 This problem is caused or worsened by the following behaviors. 89 1: In a lot of NAT implementations, a port that is available in NAT 90 is allocated for a transport session.That is, a NAT does not use a 91 port for multiple sessions simultaneously. 93 2: TIME_WAIT state assigned for a TCP connection remains active for 94 2MSL after the last ACK to the last FIN is transferred. 96 We propose two mechanisms to change the above behaviors that make it 97 possible to save addresses and ports resources. 99 1.1. TCP TIME_WAIT 101 The TCP TIME_WAIT state is described in RFC793 [RFC0793]. The TCP 102 TIME_WAIT state needs to be kept for 2MSL before a connection is 103 CLOSED, for the reasons below. 105 1: In the event that packets from a session are delayed in the in- 106 between network, and delivered to the end relatively later, we 107 should prevent the packets from being transferred and interpreted 108 as a packet that belongs to a new session. 109 2: If the remote TCP has not received the acknowledgment of its 110 connection termination request, it will re-send the FIN packet 111 several times. 113 These points are important for the TCP to work without problems. 115 1.2. TIME_WAIT Assassination 117 A TCP server MAY accept a TCP SYN for the 5-tuple session that is 118 just finished and marked as TIME_WAIT state, as far as the TCP 119 sequence number is increased. This is known as TIME-WAIT 120 assassination. It should also be noted that some assassination 121 hazards are described in RFC1337 [RFC1337]. 123 1.3. Protect Against Wrapped Sequence numbers (PAWS) 125 The TCP sequence number wraps frequently especially in a high 126 bandwidth session. PAWS is used to prevent old duplicate packets 127 that occurred in a previous session from being transferred to the new 128 session whose valid TCP sequence numbers happen to overlap with the 129 old duplicate packets. This is implemented by introducing TCP 130 timestamp option, and checking the timestamp option value of each 131 packet. PAWS is described in RFC1323 [RFC1323]. 133 2. NAT resource optimizing extension proposal 135 2.1. Port overloading mechanism 137 If destination addresses and ports are different at the outgoing 138 sessions started by local clients, NAT MAY assign the same external 139 port as the source ports at the sessions. Port overlapping mechanism 140 manages mappings between external packets and internal packets by 141 looking at and storing the 5-tuple (protocol, source address, source 142 port, destination address, destination port) of them. Thus, enables 143 concurrent use of single port for multiple transport sessions, which 144 enables NAT to work correctly in IP address resource limited network. 146 Discussions: 148 RFC4787 [RFC4787] and RFC5382 [RFC5382] requires "endpoint- 149 independent mapping" at NAT, and port overlapping NAT cannot meet the 150 requirement. This mechanism can degrade the transparency of NAT in 151 that its mapping mechanism is endpoint-dependent and makes NAT 152 traversal harder. However, if a NAT adopts endpoint-independent 153 mapping together with endpoint-dependent filtering, then the actual 154 behavior of the NAT will be the same as port overlapping NAT. It 155 should also be noted that a lot of existing NAT devices adopted this 156 port overlapping mechanism. 158 2.2. Apply RFC6191 to NAT 160 RFC 6191 [RFC6191] defines a mechanism for reducing the TIME_WAIT 161 state using TCP timestamps. This document proposes to apply this 162 RFC6191 mechanism at NAT. By tracing timestamp values in NAT that 163 manages states of traversing TCP sessions, a TIME_WAIT remaining 164 wait-time can be reduced to zero, when a TCP-SYN packet carrying a 165 larger timestamp value arrives. In this case, PAWS (Protect Against 166 Wrapped Sequence Numbers) works to discard old duplicate packets at 167 NAT. A packet can be discarded as an old duplicate if it is received 168 with a timestamp value less than a timestamp recently received on the 169 connection. When there are several clients with nonsuccessive 170 timestamp values are connected to a NAT device (i.e. not 171 monotonically increasing among clients), it prevents some clients 172 from getting a port to start a connection for a long time because 173 other clients with larger timestamp values are preferred.Two 174 workarounds for this issue are described below. 176 2.2.1. Rewrite timestamp values at NAT 178 Rewrite timestamp values of outgoings packets at NAT to be 179 monotonically increasing. 181 2.2.2. Split an assignable number of port space to each client 183 Set some rules among clients connecting to NAT, e.g., split 184 assignable ports between clients. This MAY be done by distributing 185 rules to clients via NAT equipment. 187 3. Security Considerations 189 Security issues are not discussed in this memo. 191 4. Normative References 193 [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, 194 RFC 793, September 1981. 196 [RFC1323] Jacobson, V., Braden, B., and D. Borman, "TCP Extensions 197 for High Performance", RFC 1323, May 1992. 199 [RFC1337] Braden, B., "TIME-WAIT Assassination Hazards in TCP", 200 RFC 1337, May 1992. 202 [RFC4787] Audet, F. and C. Jennings, "Network Address Translation 203 (NAT) Behavioral Requirements for Unicast UDP", BCP 127, 204 RFC 4787, January 2007. 206 [RFC5382] Guha, S., Biswas, K., Ford, B., Sivakumar, S., and P. 207 Srisuresh, "NAT Behavioral Requirements for TCP", BCP 142, 208 RFC 5382, October 2008. 210 [RFC6191] Gont, F., "Reducing the TIME-WAIT State Using TCP 211 Timestamps", BCP 159, RFC 6191, April 2011. 213 Authors' Addresses 215 Kengo Naito 216 NTT SI Lab 217 3-9-11 Midori-Cho 218 Musashino-shi, Tokyo 180-8585 219 Japan 221 Phone: +81 422 59 4949 222 Email: naito.kengo@lab.ntt.co.jp 223 Arifumi Matsumoto 224 NTT SI Lab 225 3-9-11 Midori-Cho 226 Musashino-shi, Tokyo 180-8585 227 Japan 229 Phone: +81 422 59 3334 230 Email: arifumi@nttv6.net