[Docs] [txt|pdf|xml|html] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: (draft-penno-behave-rfc4787-5382-5508-bis) 00 01 02 03 04 05 06 07 08 RFC 7857

TSVWG                                                           R. Penno
Internet-Draft                                                     Cisco
Intended status: Best Current Practice                      S. Perreault
Expires: February 13, 2016                           Jive Communications
                                                            M. Boucadair
                                                          France Telecom
                                                            S. Sivakumar
                                                                   Cisco
                                                                K. Naito
                                                                     NTT
                                                         August 12, 2015


   Network Address Translation (NAT) Behavioral Requirements Updates
             draft-ietf-tsvwg-behave-requirements-update-03

Abstract

   This document clarifies and updates several requirements of RFC4787,
   RFC5382 and RFC5508 based on operational and development experience.
   The focus of this document is NAT44.

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 February 13, 2016.

Copyright Notice

   Copyright (c) 2015 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



Penno, et al.           Expires February 13, 2016               [Page 1]


Internet-Draft draft-ietf-tsvwg-behave-requirements-update   August 2015


   carefully, as they describe your rights and restrictions with respect
   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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Scope . . . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  TCP Session Tracking  . . . . . . . . . . . . . . . . . . . .   3
     2.1.  TCP Transitory Connection Idle-Timeout  . . . . . . . . .   4
     2.2.  TCP RST . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Port Overlapping Behavior . . . . . . . . . . . . . . . . . .   5
   4.  Address Pooling Paired (APP)  . . . . . . . . . . . . . . . .   6
   5.  EIF Protocol Independence . . . . . . . . . . . . . . . . . .   6
   6.  EIF Mapping Refresh . . . . . . . . . . . . . . . . . . . . .   7
     6.1.  Outbound Mapping Refresh and Error Packets  . . . . . . .   7
   7.  EIM Protocol Independence . . . . . . . . . . . . . . . . . .   7
   8.  Port Parity . . . . . . . . . . . . . . . . . . . . . . . . .   7
   9.  Port Randomization  . . . . . . . . . . . . . . . . . . . . .   8
   10. IP Identification (IP ID) . . . . . . . . . . . . . . . . . .   8
   11. ICMP Query Mappings Timeout . . . . . . . . . . . . . . . . .   8
   12. Hairpinning Support for ICMP Packets  . . . . . . . . . . . .   9
   13. IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   14. Security Considerations . . . . . . . . . . . . . . . . . . .   9
   15. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     15.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     15.2.  Informative References . . . . . . . . . . . . . . . . .  10
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  11
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   [RFC4787], [RFC5382] and [RFC5508] greatly advanced NAT
   interoperability and conformance.  But with widespread deployment and
   evolution of Network Address Translation (NAT) more development and
   operational experience was acquired some areas of the original
   documents need further clarification or updates.  This document
   provides such clarifications and updates.

1.1.  Scope

   The goal of this document is to clarify and update the set of
   requirements listed in [RFC4787], [RFC5382] and [RFC5508].  The
   document focuses exclusively on NAT44.



Penno, et al.           Expires February 13, 2016               [Page 2]


Internet-Draft draft-ietf-tsvwg-behave-requirements-update   August 2015


   The scope of this document has been set so that it does not create
   new requirements beyond those specified in the documents cited above.
   Carrier-Grade NAT (CGN) related requirements are defined in
   [RFC6888].

1.2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   The reader is assumed to be familiar withe terminology defined in:
   [RFC2663],[RFC4787],[RFC5382], and [RFC5508].

   In this document, the term "NAT" refers to both "Basic NAT" and
   "Network Address/Port Translator (NAPT)" (see Section 3 of
   [RFC4787]).  As a reminder, Basic NAT and NAPT are two variations of
   traditional NAT, in that translation in Basic NAT is limited to IP
   addresses alone, whereas translation in NAPT is extended to include
   IP address and Transport identifier (such as TCP/UDP port or ICMP
   query ID) (refer to Section 2 of [RFC3022]).

2.  TCP Session Tracking

   [RFC5382] specifies TCP timers associated with various connection
   states but does not specify the TCP state machine a NAT44 should
   follow as a basis to apply such timers.

   Update:  The TCP state machine depicted in Figure 1, adapted from
      [RFC6146], SHOULD be implemented by a NAT for TCP session tracking
      purposes.

                    +----------------------------+
                    |                            |
                    V                            |
                 +------+   Client               |
                 |CLOSED|-----SYN------+         |
                 +------+              |         |
                     ^                 |         |
                     |TCP_TRANS T.O.   |         |
                     |                 V         |
                 +-------+          +-------+    |
                 | TRANS |          |  INIT |    |
                 +-------+          +-------+    |
                   |    ^               |        |
             data pkt   |               |        |
                   | Server/Client RST  |        |
                   |  TCP_EST T.O.      |        |



Penno, et al.           Expires February 13, 2016               [Page 3]


Internet-Draft draft-ietf-tsvwg-behave-requirements-update   August 2015


                   V    |           Server SYN   |
              +--------------+          |        |
              | ESTABLISHED  |<---------+        |
              +--------------+                   |
               |           |                     |
         Client FIN    Server FIN                |
               |           |                     |
               V           V                     |
        +---------+   +----------+               |
        |  C FIN  |   |  S FIN   |               |
        |   RCV   |   |    RCV   |               |
        +---------+   +----------+               |
            |             |                      |
        Server FIN      Client FIN            TCP_TRANS
            |             |                    T.O.
            V             V                      |
        +----------------------+                 |
        |   C FIN + S FIN RCV  |-----------------+
        +----------------------+

    Legend:
      * Messages sent to (resp. received from) the server
        are prefixed with "Server".
      * Messages sent to (resp. received from) the client
        are prefixed with "Client".
      * "C" means "Client-side"
      * "S" means "Server-side".
      * TCP_EST T.O: refers to the established connection
        idle timeout as defined in [RFC5382].
      * TCP_TRANS T.O: refers to the transitory connection
        idle timeout as defined in [RFC5382].

                          Figure 1: State Machine

2.1.  TCP Transitory Connection Idle-Timeout

   The transitory connection idle-timeout is defined as the minimum time
   a TCP connection in the partially open or closing phases must remain
   idle before the NAT considers the associated session a candidate for
   removal (REQ-5 of [RFC5382]).  But [RFC5382] does not clearly state
   whether these can be configured separately.

   Clarification:  This document clarifies that a NAT SHOULD provide
      different configurable parameters for configuring the open and
      closing idle timeouts.

      To accommodate deployments that consider a partially open timeout
      of 4 minutes as being excessive from a security standpoint, a NAT



Penno, et al.           Expires February 13, 2016               [Page 4]


Internet-Draft draft-ietf-tsvwg-behave-requirements-update   August 2015


      MAY allow to configure the timeout to be less than 4 minutes.
      Still, this specification recommends the default "transitory
      connection idle-timeout" minimum value to be set to 4 minutes.

2.2.  TCP RST

   [RFC5382] leaves the handling of TCP RST packets unspecified.

   Update:  This document adopts a similar default behavior as in
      [RFC6146].  Concretely, when the NAT receives a TCP RST matching
      an existing mapping, it MUST translate the packet according the
      NAT mapping entry.  Moreover, the NAT SHOULD wait for 4 minutes
      before deleting the session and removing any state associate with
      it if no packets are received during that 4 minutes timeout.

      Admittedly, the NAT has to verify whether received TCP RST packets
      belong to a connection.  These verification checks are required to
      avoid off-path attacks.

      If the NAT removes immediately the NAT mapping upon receipt of a
      TCP RST message, stale connections may be maintained by endpoints
      if the first RST message is lost between the NAT and the
      recipient.

3.  Port Overlapping Behavior

   REQ-1 from [RFC4787] and REQ-1 from [RFC5382] specify a specific port
   overlapping behavior; that is the external IP address and port can be
   reused for connections originating from the same internal source IP
   address and port irrespective of the destination.  This is known as
   endpoint-independent mapping (EIM).

   Update:  This document clarifies that this port overlapping behavior
      may be extended to connections originating from different internal
      source IP addresses and ports as long as their destinations are
      different.

      The following mechanism MAY be implemented by a NAT:

         If destination addresses and ports are different for outgoing
         connections started by local clients, a NAT MAY assign the same
         external port as the source ports for the connections.  The
         port overlapping mechanism manages mappings between external
         packets and internal packets by looking at and storing their
         5-tuple (protocol, source address, source port, destination
         address, destination port).





Penno, et al.           Expires February 13, 2016               [Page 5]


Internet-Draft draft-ietf-tsvwg-behave-requirements-update   August 2015


      This enables concurrent use of a single NAT external port for
      multiple transport sessions, which allows a NAT to successfully
      process packets in an IP address resource limited network (e.g.,
      deployment with high address space multiplicative factor (refer to
      Appendix B.  of [RFC6269])).

4.  Address Pooling Paired (APP)

   The Address Pooling Paired (APP) behavior for a NAT was recommended
   in REQ-2 from [RFC4787], but the behavior when a public IPv4 runs out
   of ports was left undefined.

   Clarification:  This document clarifies that if APP is enabled, new
      sessions from a host that already has a mapping associated with an
      external IP that ran out of ports SHOULD be dropped.

      The administrator MAY provide a configurable parameter that allows
      a NAT to starting using ports from another external IP address
      when the one that anchored the APP mapping ran out of ports.  This
      is a trade-off between service continuity and APP strict
      enforcement.  (Note, this behavior is sometimes referred as 'soft-
      APP'.)

   Update:  This behavior SHOULD apply also for TCP.

5.  EIF Protocol Independence

   REQ-8 from [RFC4787] and REQ-3 from [RFC5382] do not specify whether
   EIF mappings are protocol-independent.  In other words, if an
   outbound TCP SYN creates a mapping, it is left undefined whether
   inbound UDP packets destined to that mapping should be forwarded.

   Update:  This document specifies that EIF mappings SHOULD be
      protocol-independent in order allow inbound packets for protocols
      that multiplex TCP and UDP over the same IP address and port
      through the NAT and also maintain compatibility with stateful
      NAT64 . The administrator MAY provide a configuration parameter to
      make it protocol-dependent.  The default value of this
      configuration parameter is to allow for protocol-independent EIF.

      Applications that can be transported over a variety of transport
      protocols and/or support transport fall back schemes won't
      experience connectivity failures as a function of the underlying
      transport protocol or the filtering mode enabled at the NAT.







Penno, et al.           Expires February 13, 2016               [Page 6]


Internet-Draft draft-ietf-tsvwg-behave-requirements-update   August 2015


6.  EIF Mapping Refresh

   The NAT mapping Refresh direction may have a "NAT Inbound refresh
   behavior" of "True" according to REQ-6 from [RFC4787], but [RFC4787]
   does not clarify how this behavior applies to EIF mappings.  The
   issue in question is whether inbound packets that match an EIF
   mapping but do not create a new session due to a security policy
   should refresh the mapping timer.

   Clarification:  This document clarifies that even when a NAT has an
      inbound refresh behavior set to 'TRUE', such packets SHOULD NOT
      refresh the mapping.  Otherwise a simple attack of a packet every
      2 minutes can keep the mapping indefinitely.

   Update:  This behavior SHOULD apply also for TCP.

6.1.  Outbound Mapping Refresh and Error Packets

   Update:  In the case of NAT outbound refresh behavior there are
      certain types of packets that should not refresh the mapping even
      if their direction is outbound.  For example, if the mapping is
      kept alive by ICMP Errors or TCP RST outbound packets sent as
      response to inbound packets, these SHOULD NOT refresh the mapping.

7.  EIM Protocol Independence

   REQ-1 from [RFC4787] and REQ-1 from [RFC5382] do not specify whether
   EIM are protocol-independent.  In other words, if a outbound TCP SYN
   creates a mapping it is left undefined whether outbound UDP can reuse
   such mapping and create session.  On the other hand, stateful NAT64
   [RFC6146] clearly specifies three binding information bases (TCP,
   UDP, ICMP).

   Update:  EIM mappings SHOULD be protocol-dependent.  A configuration
      parameter MAY be provided in order allow protocols that multiplex
      TCP and UDP over the same source IP address and port number to use
      a single mapping.

8.  Port Parity

   Update:  A NAT MAY disable port parity preservation for all dynamic
      mappings.  Nevertheless, A NAT SHOULD support means to explicitly
      request to preserve port parity (e.g., [I-D.ietf-pcp-port-set]).

      Note: According to [RFC6887], dynamic mappings are said to be
      dynamic in the sense that they are created on demand, either
      implicitly or explicitly:




Penno, et al.           Expires February 13, 2016               [Page 7]


Internet-Draft draft-ietf-tsvwg-behave-requirements-update   August 2015


      1.  Implicit dynamic mappings refer to mappings that are created
          as a side effect of traffic such as an outgoing TCP SYN or
          outgoing UDP packet.  Implicit dynamic mappings usually have a
          finite lifetime, though this lifetime is generally not known
          to the client using them.

      2.  Explicit dynamic mappings refer to mappings that are created
          as a result, for example, of explicit PCP MAP and PEER
          requests.  Explicit dynamic mappings have a finite lifetime,
          and this lifetime is communicated to the client.

9.  Port Randomization

   Update:  A NAT SHOULD follow the recommendations specified in
      Section 4 of [RFC6056], especially:

         "A NAPT that does not implement port preservation [RFC4787]
         [RFC5382] SHOULD obfuscate selection of the ephemeral port of a
         packet when it is changed during translation of that packet.  A
         NAPT that does implement port preservation SHOULD obfuscate the
         ephemeral port of a packet only if the port must be changed as
         a result of the port being already in use for some other
         session.  A NAPT that performs parity preservation and that
         must change the ephemeral port during translation of a packet
         SHOULD obfuscate the ephemeral ports.  The algorithms described
         in this document could be easily adapted such that the parity
         is preserved (i.e., force the lowest order bit of the resulting
         port number to 0 or 1 according to whether even or odd parity
         is desired)."

10.  IP Identification (IP ID)

   Update:  A NAT SHOULD handle the Identification field of translated
      IPv4 packets as specified in Section 5.3.1 of [RFC6864].

   Discussion:  This recommendation may have undesired effects on the
      performance of the NAT in environments in which fragmentation is
      massively experienced.  Such issue can be used as an attack vector
      against NATs.

11.  ICMP Query Mappings Timeout

   Section 3.1 of [RFC5508] precises that ICMP Query Mappings are to be
   maintained by a NAT.  However, the specification doesn't discuss
   Query Mapping timeout values.  Section 3.2 of [RFC5508] only
   discusses ICMP Query Session Timeouts.





Penno, et al.           Expires February 13, 2016               [Page 8]


Internet-Draft draft-ietf-tsvwg-behave-requirements-update   August 2015


   Update:  ICMP Query Mappings MAY be deleted once the last the session
      using the mapping is deleted.

12.  Hairpinning Support for ICMP Packets

   REQ-7 from [RFC5508] specifies that a NAT enforcing 'Basic NAT' must
   support traversal of hairpinned ICMP Query sessions.

   Clarification:  This implicitly means that address mappings from
      external address to internal address (similar to Endpoint
      Independent Filters) must be maintained to allow inbound ICMP
      Query sessions.  If an ICMP Query is received on an external
      address, a NAT can then translate to an internal IP.

   REQ-7 from [RFC5508] specifies that all NATs must support the
   traversal of hairpinned ICMP Error messages.

   Clarification:  This behavior requires a NAT to maintain address
      mappings from external IP address to internal IP address in
      addition to the ICMP Query Mappings described in Section 3.1 of
      [RFC5508].

13.  IANA Considerations

   This document does not require any IANA action.

14.  Security Considerations

   NAT behavioral considerations are discussed in [RFC4787].

   Security considerations discussed in Section 5 of [RFC6146] apply
   also fro NAT44.

   In the case of EIF mappings due to high risk of resource crunch, a
   NAT MAY provide a configurable parameter to limit the number of
   inbound sessions spawned from a EIF mapping.

15.  References

15.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.






Penno, et al.           Expires February 13, 2016               [Page 9]


Internet-Draft draft-ietf-tsvwg-behave-requirements-update   August 2015


   [RFC4787]  Audet, F., Ed. and C. Jennings, "Network Address
              Translation (NAT) Behavioral Requirements for Unicast
              UDP", BCP 127, RFC 4787, DOI 10.17487/RFC4787, January
              2007, <http://www.rfc-editor.org/info/rfc4787>.

   [RFC5382]  Guha, S., Ed., Biswas, K., Ford, B., Sivakumar, S., and P.
              Srisuresh, "NAT Behavioral Requirements for TCP", BCP 142,
              RFC 5382, DOI 10.17487/RFC5382, October 2008,
              <http://www.rfc-editor.org/info/rfc5382>.

   [RFC5508]  Srisuresh, P., Ford, B., Sivakumar, S., and S. Guha, "NAT
              Behavioral Requirements for ICMP", BCP 148, RFC 5508,
              DOI 10.17487/RFC5508, April 2009,
              <http://www.rfc-editor.org/info/rfc5508>.

   [RFC6056]  Larsen, M. and F. Gont, "Recommendations for Transport-
              Protocol Port Randomization", BCP 156, RFC 6056,
              DOI 10.17487/RFC6056, January 2011,
              <http://www.rfc-editor.org/info/rfc6056>.

   [RFC6146]  Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
              NAT64: Network Address and Protocol Translation from IPv6
              Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146,
              April 2011, <http://www.rfc-editor.org/info/rfc6146>.

   [RFC6864]  Touch, J., "Updated Specification of the IPv4 ID Field",
              RFC 6864, DOI 10.17487/RFC6864, February 2013,
              <http://www.rfc-editor.org/info/rfc6864>.

   [RFC6888]  Perreault, S., Ed., Yamagata, I., Miyakawa, S., Nakagawa,
              A., and H. Ashida, "Common Requirements for Carrier-Grade
              NATs (CGNs)", BCP 127, RFC 6888, DOI 10.17487/RFC6888,
              April 2013, <http://www.rfc-editor.org/info/rfc6888>.

15.2.  Informative References

   [I-D.ietf-pcp-port-set]
              Qiong, Q., Boucadair, M., Sivakumar, S., Zhou, C., Tsou,
              T., and S. Perreault, "Port Control Protocol (PCP)
              Extension for Port Set Allocation", draft-ietf-pcp-port-
              set-09 (work in progress), May 2015.

   [RFC2663]  Srisuresh, P. and M. Holdrege, "IP Network Address
              Translator (NAT) Terminology and Considerations",
              RFC 2663, DOI 10.17487/RFC2663, August 1999,
              <http://www.rfc-editor.org/info/rfc2663>.





Penno, et al.           Expires February 13, 2016              [Page 10]


Internet-Draft draft-ietf-tsvwg-behave-requirements-update   August 2015


   [RFC3022]  Srisuresh, P. and K. Egevang, "Traditional IP Network
              Address Translator (Traditional NAT)", RFC 3022,
              DOI 10.17487/RFC3022, January 2001,
              <http://www.rfc-editor.org/info/rfc3022>.

   [RFC6269]  Ford, M., Ed., Boucadair, M., Durand, A., Levis, P., and
              P. Roberts, "Issues with IP Address Sharing", RFC 6269,
              DOI 10.17487/RFC6269, June 2011,
              <http://www.rfc-editor.org/info/rfc6269>.

   [RFC6887]  Wing, D., Ed., Cheshire, S., Boucadair, M., Penno, R., and
              P. Selkirk, "Port Control Protocol (PCP)", RFC 6887,
              DOI 10.17487/RFC6887, April 2013,
              <http://www.rfc-editor.org/info/rfc6887>.

Acknowledgements

   Thanks to Dan Wing, Suresh Kumar, Mayuresh Bakshi, Rajesh Mohan, Lars
   Eggert, and Gorry Fairhurst for their review and discussion.

Contributors

   The following individual contributed text to the document:

      Sarat Kamiset, Insieme Networks, United States

Authors' Addresses

   Reinaldo Penno
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose, California  95134
   USA

   Email: repenno@cisco.com


   Simon Perreault
   Jive Communications
   Canada

   Email: sperreault@jive.com









Penno, et al.           Expires February 13, 2016              [Page 11]


Internet-Draft draft-ietf-tsvwg-behave-requirements-update   August 2015


   Mohamed Boucadair
   France Telecom
   Rennes  35000
   France

   Email: mohamed.boucadair@orange.com


   Senthil Sivakumar
   Cisco Systems, Inc.
   United States

   Email: ssenthil@cisco.com


   Kengo Naito
   NTT
   Tokyo
   Japan

   Email: k.naito@nttv6.jp






























Penno, et al.           Expires February 13, 2016              [Page 12]


Html markup produced by rfcmarkup 1.129c, available from https://tools.ietf.org/tools/rfcmarkup/