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NSIS Working Group                                               C. Aoun
Internet-Draft                                           Nortel Networks
Expires: August 16, 2004                                      M. Brunner
                                                          M. Stiemerling
                                                               M. Martin
                                                                     NEC
                                                           H. Tschofenig
                                                                 Siemens
                                                       February 16, 2004


               NAT/Firewall NSLP Migration Considerations
                draft-aoun-nsis-nslp-natfw-migration-01

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 August 16, 2004.

Copyright Notice

   Copyright (C) The Internet Society (2004). All Rights Reserved.

Abstract

   This document discusses migration issues towards NSIS NAT/FW NSLP
   enabled NATs and Firewalls. The document will serve as input to the
   NSIS NATFW NSLP document.







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Table of Contents

   1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . .   3

   2. Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .   4

   3. NSIS unaware NAT Traversal . . . . . . . . . . . . . . . . . .   5

   4. Unilateral NSIS signaling  . . . . . . . . . . . . . . . . . .   8

   5. NSIS unaware Firewall Traversal  . . . . . . . . . . . . . . .  13

   6. NATFW NSLP NTLP requirements . . . . . . . . . . . . . . . . .  14

   7. Security Considerations  . . . . . . . . . . . . . . . . . . .  15

   8. Open issues  . . . . . . . . . . . . . . . . . . . . . . . . .  16

      Normative References . . . . . . . . . . . . . . . . . . . . .  17

      Informative References . . . . . . . . . . . . . . . . . . . .  18

      Authors' Addresses . . . . . . . . . . . . . . . . . . . . . .  18

      Intellectual Property and Copyright Statements . . . . . . . .  20


























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1. Introduction

   The overall NSIS protocol suite (including the NATFW NSLP) is
   impacted by NSIS NATFW NSLP unaware NATs and Firewalls, this document
   covers impacts as well as some suggestions to ease the deployments of
   the NSIS protocol suite until the installed base on NATs and
   Firewalls migrates to NSIS.

   The NATFW NSLP should allow an end host supporting NSIS to operate
   properly without the need of supporting true end-to-end NSIS
   signaling to its application correspondent. This is very practical
   during the initial phases of the NSIS migration and is applicable in
   simple network configurations not affected by asymmetric routing. In
   the early phases of the NSIS NATFW NSLP migration, this situation
   will occur quite frequent and hence this scenario must be supported.

   The NSIS protocol should traverse NSIS unaware NATs (and possibly
   Firewalls) to allow a smoother deployment of, for example, Qos NSLP
   in today's networks. To provide a smooth migration it is necessary to
   understand the coexistence of NSIS aware and unware NATs and
   Firewalls.






























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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 [1].

   The terminology used in this document is defined in [2].












































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3. NSIS unaware NAT Traversal

   This section discusses how an NE with any NSLP could still operate
   when an NSIS unaware NAT is on the data path. The detection of an
   NSIS unaware NAT could be a feature of the NTLP [3], allowing its
   usage on any NE regardless of the supported NSLPs.

   Several NSIS independent approaches could be used by the NE to learn
   its global scoped address in order to use it for its hosted NSLPs. In
   this version of the document, only the STUN protocol [5] is
   considered as means to acquire the global scoped address; the next
   versions will consider other approaches.

    +---------------------------------------+
    |                                       |          +--------+
    | +----------+                          |          | STUN   |
    | |Apps      |                          |          | Server |
    | +----------+                     +---+|          +--------+
    | | STUN     |                     |NAT||
    | | CLIENT   |                     |   ||
    | |__________|                     +---+|
    | |ANY_NSLP  |                          |
    | |  NI/NR   |                          |
    | +----------+                          |
    |  Host A                               |
    +---------------------------------------+

               Figure 1: STUN usage for NSIS unaware NATs

   Within the initial stages of the NSIS migration, NE functions will be
   co-hosting a STUN client that was already present on the application
   end-host. Within Host A, shown in Figure 1, the NSIS API could invoke
   the services of the STUN client (as shown in Figure 2) upon
   determination that an NSIS unaware NAT was on the path.This would
   allow applications using UDP transport to work (only applicable for
   cone NAT variants [5]).


                    +-----------------+
         ___________| NSIS aware NAT  |_________
         |          | Determination   |        |
   NSIS  |          +-----------------+        |  NSIS
   Aware |                                     |  Unaware
         |                                     |
         |                                     |
         V                                     V
    +-------------------+                +------------+
    |Proceed with       |     If not UDP |Used data   |



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    |normal NR operation|       +--------|transport   |
    +-------------------+       |        |protocol    |
                                |        +------------+
                                |              |  If UDP
                                V              |
                         +-------------+       |
                         |Log error    |       |
                         |to app layer |       |
                         +-------------+       V
                                         +-------------+
                                         | Invoke STUN |
                                         | Client      |
                                         +------+------+
                                                     |
                                                     |
                                                     |
                                                     V
                                                +------------+
                                                | Send STUN  |
                                                |   binding  |
                                                |  request   |
                                                +-----+------+
                                                      |
                                                 V
                                    +-------------------------+
                                    |Standard STUN operations |
                                    +-------------------------+

               Figure 2: Interactions with a STUN client

   NSLPs would use the STUN returned global scoped address for the flow
   id [3].To allow NSIS signaling to be received by the NR on host A,
   without impacting existing applications (i.e. without explicitly
   providing the address and port of the NSIS recipient in the
   application signaling), the NSIS protocols would need to use NTLP
   datagram mode transport (as defined in [3]). This would imply that
   the NTLP will be using the same port as the data flows, this might
   complicate the proposed mode of operations (and might not meet the
   expected performance). The next version of the draft will discuss
   whether this approach would be practical based on received feedback
   from implementors.

   Subsequently we discuss how the NATFW NSLP could co-exist with
   interim NAT traversal mechanisms described in [8]. In Figure 3, a
   STUN client (Host A) [5], an NE (Host B), a host using a Media Proxy
   [8] and host using a TURN client [9] co-exist in the same network
   with a NATFW NSLP aware NAT. There are no reasons for the existing
   mechanisms to be mutually exclusive every host could continue using



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   the existing interim solutions, meanwhile the unilateral NSIS
   signaling would be used until both ends support the NSIS NATFW NSLP.



   +---------------------------+
   |                          _|__1______.STUN Server
   |STUN Client ----'''''''''' |
   | Host A                    |                    App server
   |              2   _..NAT++ |                     .-'
   | NI/NR     __.--''         |                 3 .'+
   | Host B -''                |      Media Proxy.-'
   |                           |
   |                           |
   | Host C                    |
   |                      4    |
   | Turn Client---------------+---------- TURN Server
   | Host D                    |
   |                           |
   +---------------------------+

  Figure 3: Coexistence of NSIS NATFW NSLP and existing NAT traversal
                               mechanisms




























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4. Unilateral NSIS signaling

   When NSIS NAT/FW signaling will start to be deployed, it is quite
   possible that an NI sends an NSIS message without having an NR to
   respond to it. The NATFW NSLP should be able to handle this type of
   deployments. NSIS NATFW NSLP signaling for NAT binds is already local
   within the trust domain (the Reserve External Address is intercepted
   by the edge NAT, ref [2], however this is not the case with firewall
   signaling that should be end to end.

   Since the purpose of this section is to discuss how are end to end
   signaled messages handled when no NRs are available on the end-host
   only Firewalls (the NFs) are discussed within the example networks.

   There are two interesting cases to be analyzed:

   Approach 1: Implicit (not explicitly scoped) localized signaling: The
      local trust domain (from an NI perspective) has at least one NSIS
      aware Firewall, there is no NR on the far end as well as no NSIS
      aware NAT or Firewall. This approaches is similar to [13], however
      the NSIS messages do not included any scoping information. Figure
      4 shows this scenario graphically.

   +-----------------------+                    +--------------------+
   |+----------+           |                    |         +----------+
   ||App client|           |                    |         |App client|
   ||NI/NR     |      FW++ |      ,---------.   |         +----------+
   |+----------+           ''''''' The net   ---.            Host B  |
   | Host A                |      `---------'   |                    |
   |                       |                    |                    |
   |      Net A            |                    |     Net B          |
   +-----------------------+                    +--------------------+


                 Figure 4: Implicit localized signaling

   Approach 2: Missing trust with far end host's NFs: The local trust
      domain has no NSIS aware Firewall, there is no NR at the far end
      but there is at least an NSIS aware firewall with which the local
      NI has no direct trust relation (which implies an authorization
      issue and possibly authentication issues). The main addition to
      the issue discussed in the localized signaling case above
      (determination of the last NE on the path and response to the NSIS
      message by the last NE) is the lack of trust relations with the
      NI. Figure 5 shows this scenario graphically.






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   +-----------------------+                    +--------------------+
   |+----------+           |                    |         +----------+
   ||App client|           |                    |         |App client|
   ||NI/NR     |           |      ,---------.   | FW++    +----------+
   |+----------+           ''''''' The net   ---.            Host B  |
   | Host A                |      `---------'   |                    |
   |                       |                    |                    |
   |       Net A           |                    |      Net B         |
   +-----------------------+                    +--------------------+


         Figure 5: Missing trust with the remote host's network

   In approach (1), the NI sends its firewall policy rule creation
   message, it traverses the first NF (its own firewall) but there is no
   NR to respond back. If we consider to have a response timer on the
   last NF being traversed by an NATFW NSLP message then if no response
   is received to the NSIS message, the last NF will respond back to the
   NI with a notification of no far end NR response. This will imply
   that the signaling will be scoped to the last NF on the path that
   responded back. Using the network deployment shown in Figure 4, the
   following mode of operation would apply:


    Host A                                    Host B
    NI                 FW++                 Expected NR
     |                  |                    |
     |1-NSIS Init msg   |                    |
     |----------------> |                    |
     |                  |2-NSIS Init msg     |
     |                  | +--------------->  |
     |                  | |NATFW NSLP ON     |
     |                  | |                  |
     |                  | |                  |
     |                  | |                  |
     |                  | | Timeout          |
     3-NSIS Init msg Ack| V                  |
     |No NR             |                    |
     |<.................|                    |

                 Figure 6: Detecting the last NSIS peer

   Figure 7 provides the message sequences when more than one NSIS aware
   NAT or Firewall is deployed within the same trust domain. Upon
   determination of a previous NSIS hop, an NSIS aware node will notify
   the previous NSIS hop of its existence to avoid launching the timer
   that triggers sending of an NSIS message back to the NI. The current
   NTLP message association establishment procedures supports this



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   behavior. The last NF on the path will launch the timer since no
   valid downstream NSIS neighbor responded back.


                     Trust domain A               Trust domain B
    <..........................................>      <-------->
    Host A                                            Host B
    NI                  FW++               FW++       Expected NR
     |                   |                  |                 |
     |  NSIS Init msg    |                  |                 |
     | ----------------> |  NSIS Init msg   |                 |
     |                   | ---------------> | NSIS Init msg   |
     |                   |  NATFW NSLP ON   |---------------->|
     |                   |                  | |  with Token   |
     |                   | Valid            . | NATFW NSLP ON |
     |                   | NSIS Neighbor    | |               |
     |                   |<-----------------| |               |
     |                   |----------------->| | Timeout       |
     |                   |  Ack             | |               |
     |                   |                  | |               |
     |                   |                  | |               |
     |                   |                  | |               |
     |                   |                  | V               |
     |                   | <................+                 |
     |                   | NSIS Init msg Ack|                 |
     | NSIS Init msg Ack | No NR            |                 |
     | No NR             |                  |                 |
     | <.................|                  |                 |

         Figure 7: Detecting the last NSIS peer (multiple FWs)

   In approach (2), the NI sends its firewall policy rule creation
   message, it traverses the FW hosted in Host B's network, but host A
   is not authorized to install a policy rule unless the policy rule
   creation is approved by a trusted entity within Net B. Unfortunately
   Host B was not yet upgraded to support the NATFW NSLP, another entity
   needs to authorize the policy rule installation.
   Potentially a trusted third party already aware of the application
   session held between Host A and Host B could provide an authorization
   token to Host A [11], the token would be encapsulated within the
   NATFW NSLP message and would allow the NSIS aware Firewall in Net B
   to authorize Host A's requested policy rule to be installed. This
   approach would obviously require to put in place a mechanism to
   provide the authorization token to Host A. The token could be
   requested by the NI and included in the NSLP signaling by default or
   after receiving an error message from the far end NSIS aware Firewall
   indicating that authorization data is required. The authorization
   token would need to be associated with the identity of the NI,



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   associating the authorization token with an IP address is not
   sufficient, and could lead to issues if the IP address was not valid
   due to address translation occurring on the path, a proper mechanism
   should be put in place to allow proper authentication of the entitled
   token user.

   Figure 8 shows the architecture with two different networks and the
   trusted third party which creates the authorization. Figure 9
   provides a message flow for authorization token handling.


                               +---------------+
                               |  Authorization|1-Generate Token
                               |   mediator    |
                              .'--------------+
                            .'            \
         2-Provide       .-'               \
           Token       .'                   \
                     .'                      \
                   .'                         \4-Check token
                 .-'                            \ validity
   +-----------.'----------+                    ++----------------+
   |+--------.'+           |                    | \    +----------+
   ||App client|           |                    |  \   |App client|
   ||NI/NR     +-------.   |      ,-=.----.-.   | FW++ +----------+
   |+----------+        `---------'The net `--------      Host B  |
   | Host A                |      `---------'   |                 |
   |                       |          3-Send    |                 |
   | Network A             |      NSLP msg with | Network B       |
   +-----------------------+      Token         +-----------------+

                 Figure 8: Authorization Token Handling



















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         Trust domain A                         Trust domain B
    <........................>           <--------------------->
    Host A                                            Host B
    NI                  FW                 FW++       Expected NR
     |                   |                  |                 |
     |  NSIS Init msg    |                  |                 |
     | ------------------+----------------> |                 |
     |                   |                  |  NSIS Init msg  |
     |                   |                  | +-------------->|
     |                   |                  |  NATFW NSLP ON  |
     |                   | NSIS ERROR       .                 |
     | <....................................|                 |
     |                   |Need Authorization|                 |
     |  NSIS Init msg    |                  |                 |
     | ------------------------------------>|                 |
     |  with Token       |                  |                 |
     |                   |                  | NSIS Init msg   |
     |                   |                  |---------------->|
     |                   |                  | |  with Token   |
     |                   | Valid            + | NATFW NSLP ON |
     |                   | NSIS Neighbor    | |               |
     |                   |<-----------------| | Timeout       |
     |                   |----------------->| |               |
     | NSIS Init msg Ack |  Ack             | |               |
     | No NR             | <................| V               |
     | <.................| NSIS Init msg Ack|                 |
     |                   | No NR            |                 |


               Figure 9: Authorization Token Message Flow





















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5. NSIS unaware Firewall Traversal

   In case an NSIS unaware firewall is traversed by NSIS messages, NSIS
   messages should be allowed to go through it, as well as the exchanged
   data flows between the user application clients. This is not
   necessarily an obvious task to perform in case the NSIS messages
   cannot be identified by the NSIS unaware firewall. Same applies for
   the user application data flows.

   NSIS message identification should be supported by existing
   firewalls.
   Currently firewalls support flow identification by using the 5 tuple
   or a sub-set of it. The authors are still expecting feedback from
   firewall vendors to see if we can assume that existing firewalls will
   not drop packets including the the Router Alert Option (RAO) [12]. In
   case existing firewalls drop packets having the router alert option,
   then the RAO should not be the only element of the used
   identification filter.

   User application data flow identification, should be deterministic at
   a specific address and port range level. This means that the
   application clients uses a combination of an address and specific
   transport port range.This combination should be configured on the
   firewall.

   In case a NAT is deployed on the path and it is NSIS-NATFW, the
   assigned bind should be consistent with policy rules configured with
   the NSIS unaware firewall.

   Even though the deployed Firewall is not NSIS aware, the application
   data would still be forwarded if existing interim solutions were used
   such as a mix of stateless policy rules and flow based states with
   initial packets sent in the outbound direction (inside to outside a
   trust domain).

















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6. NATFW NSLP NTLP requirements

   In this section we list two requirements for the NTLP raised by this
   document.

   o  When NSIS signaling is used in presence of NSIS unware NATs then
      raw IP MUST NOT be used. Network address and port translation
      requires transport layer identifiers as mean to direct inbound
      traffic to the right recipient.

   o  If IPsec is used to secure NSIS signaling messages then UDP
      encapsulation for IPsec protected packets (see [4]) MUST be used
      to ensure that IPsec does not break. IKE with extensions or IKEv2
      is able to detect the presence of a NAT along the path.





































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7. Security Considerations

   This document discusses various security issues for NAT/Firewall
   signaling in migration scenarios.

   Further security considerations can be found in [2].













































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8. Open issues

   Working on this document we identified to the following open issues
   and actions that need to be taken:

   o  Add a network centric solution to address interim deployment
      phases where the end host doesn't support yet the NSIS protocol
      suite.

   o  Provide updates on the RAO firewall issues

   o  Update Section 3 with regards to the multiplexing/demultiplexing
      of NSIS messages and user data on the same socket.

   o  Move the mediated authorization discussion in Section 4 to [2]




































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Normative References

   [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", March 1997.

   [2]  Stiemerling, M., Martin, M., Tschofenig, H. and C. Aoun, "A NAT/
        Firewall NSIS Signaling Layer Protocol (NSLP)", DRAFT
        draft-ietf-nsis-nslp-natfw-01.txt, February 2004.

   [3]  "GIMPS: General Internet Messaging Protocol for Signaling",
        draft-draft-ietf-nsis-ntlp-00 (work in progress), October 2003.








































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Informative References

   [4]   A. Huttunen et all, A., "UDP Encapsulation of IPsec Packets",
         DRAFT draft-ietf-ipsec-udp-encaps-07.txt, Jan 2003.

   [5]   Rosenberg, J., Weinberger, J., Huitema, C. and R. Mahy, "STUN -
         Simple Traversal of User Datagram Protocol (UDP) Through
         Network Address Translators (NATs)", RFC 3489, March 2003.

   [6]   Handley, M. and V. Jacobson, "SDP: Session Description
         Protocol", RFC 2327, April 1998.

   [7]   ITU-T SG16, "Packet-based multimedia communications systems",
         ITU-T H.323, November 2000.

   [8]   Rosenberg, J., "NAT and Firewall Scenarios and Solutions for
         SIP", draft-rosenberg-sipping-nat-scenarios-00 (work in
         progress), November 2001.

   [9]   Rosenberg, J., "Traversal Using Relay NAT (TURN)",
         draft-rosenberg-midcom-turn-01 (work in progress), March 2003.

   [10]  Swale, R., Mart, P., Sijben, P., Brim, S. and M. Shore,
         "Middlebox Communications (midcom) Protocol Requirements", RFC
         3304, August 2002.

   [11]  Hamer, L-N., Gage, B. and H. Shieh, "Framework for Session
         Set-up with Media Authorization", RFC 3521, April 2003.

   [12]  Katz, D., "IP Router Alert Option", RFC 2113, February 1997.

   [13]  Manner, J., "Localized RSVP", draft-manner-lrsvp-03 (work in
         progress), January 2004.


Authors' Addresses

   Cedric Aoun
   Nortel Networks

   France

   EMail: cedric.aoun@nortelnetworks.com








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   Marcus Brunner
   Network Laboratories, NEC Europe Ltd.
   Kurfuersten-Anlage 36
   Heidelberg  69115
   Germany

   Phone: +49 (0) 6221 905 11 29
   EMail: brunner@ccrle.nec.de
   URI:   http://www.brubers.org/marcus


   Martin Stiemerling
   Network Laboratories, NEC Europe Ltd.
   Kurfuersten-Anlage 36
   Heidelberg  69115
   Germany

   Phone: +49 (0) 6221 905 11 13
   EMail: stiemerling@ccrle.nec.de
   URI:


   Miquel Martin
   Network Laboratories, NEC Europe Ltd.
   Kurfuersten-Anlage 36
   Heidelberg  69115
   Germany

   Phone: +49 (0) 6221 905 11 16
   EMail: miquel.martin@ccrle.nec.de
   URI:


   Hannes Tschofenig
   Siemens AG
   Otto-Hahn-Ring 6
   Munich  81739
   Germany

   Phone:
   EMail: Hannes.Tschofenig@siemens.com
   URI:









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Acknowledgment

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Aoun, et al.            Expires August 16, 2004                [Page 21]


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