Internet DRAFT - draft-sivakumar-behave-edm-harmful

draft-sivakumar-behave-edm-harmful






Behave                                                      S. Sivakumar
Internet-Draft                                             Cisco Systems
Intended status: Informational                             March 5, 2012
Expires: September 6, 2012


                Issues with End-point dependent mapping
                 draft-sivakumar-behave-edm-harmful-00

Abstract

   Some NAT devices implement the End-point dependent mapping and
   filtering behavior.  This document describes the issues that would
   arise with End-point dependent mapping and filtering behavior.

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   This Internet-Draft will expire on September 6, 2012.

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Table of Contents

   1.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . . . 3
   3.  Why is End-point dependent mapping and filtering used . . . . . 4
   4.  Peer to Peer applications . . . . . . . . . . . . . . . . . . . 5
   5.  Issues with End-point dependent mapping and filtering . . . . . 5
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 5
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   8.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     9.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
     9.2.  Informative References  . . . . . . . . . . . . . . . . . . 6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 6




































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1.  Terminology

   The usage of the term "NAT device" in this document refer to any
   NAT44 and NAT64 devices.

   Address dependent end-point mapping - A NAT device creates a mapping
   taking into account the destination address and port.  The same
   mapping is reused if a packet from the same source address, source
   port destined to the same destination address.

   Address and port dependent end-point mapping - A NAT device creates a
   mapping taking into account the destination address and port.  The
   same mapping is reused if a packet from the same source address,
   source port destined to the same destination address and destination
   port.

   End-point dependent mapping - A NAT device that does either Address
   dependent mapping and/or Address and port dependent mapping is
   referred to follow End-point dependent mapping.

   Address dependent end-point filtering - A NAT device that allows
   inbound traffic to the internal hosts only if the internal host had
   previously communicated to the external address.

   Address and port dependent end-point filtering - A NAT device that
   allow inbound traffic to the internal hosts only if the internal host
   had previously communicated to the same external address and port.

   End-point dependent filtering - A NAT device that filters the
   incoming traffic based on the external hosts' source address and/or
   port.


2.  Introduction

   End-point dependent mapping and filtering is still prevalent in many
   NAT devices.  Even though [RFC4787] and [RFC5382] recommends against
   using end point dependent mapping and filtering, these two RFCs does
   not go into the details of why it is end point dependent mapping is
   bad for applications.  This document focuses on the negative impacts
   of End point dependent mapping and filtering on applications.

2.1.  Requirements Language

   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].




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3.  Why is End-point dependent mapping and filtering used

   There are two main reasons that End-point dependent mapping and
   filtering is used. a.  End-point independent mapping can be used to
   extend the number of ports available per global address, often
   referred to as port overloading.  For example, if there are two hosts
   behind the same NAT device

        +---------+  X1,x1                     P,p     +---------+
        |   X1    |---------+                +---------|   Y1    |
        +---------+         |   +--------+   |         +---------+
                            |---|  NAT   |---|
        +---------+         |   +--------+   | P,p     +---------+
        |   X2    |---------+                +---------|   Y2    |
        +---------+   X2, x2                           +---------+


                                 Figure 1

   Host X1 (X1, x1) initiating communication to destination (Y1, y1) and
   host X2 (Y1, y1) initiating communication to destination (Y2, y2).

   NAT device will translate the source address and port (X1, x1) to
   public address (P, p) and it will translate the source address and
   port (X2, x2) also to public address and port (P, p), as long as both
   the hosts are not destined to the same end point.  In order to
   correctly demultiplex the return packets, the NAT device will store
   the destination information.  So, when the return packet from (Y1,
   y1) to (P, p) is seen the NAT device can translate the destination to
   (X1, x1).  Similarly, when the return packet from (Y2, y2) destined
   to (P, p) is seen, the destination will be translated to (X2, x2).
   As can be seen with this example, the same external port p can be
   used for multiple flows thus by maximizing the use of a single
   external IPv4 address.

   This kind of implementation also gives a perception that the NAT
   device is actually doing end-point dependent filtering.

   The End-point dependent filtering is perceived to offer security.
   Since the outbound packet was sent to the external address, it is
   assumed that is a trusted entry.  Hence the return packets from the
   same external address is assumed to be trusted and doing filtering
   based on the external address and port is perceived to offer
   security.

   Secondly, most of the client server based applications with End-point
   dependent filtering will work fine.  This leads one to believe that
   End-point dependent filtering will work for all other applications as



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   well.


4.  Peer to Peer applications

   Peer to Peer (P2P) applications use a variety of techniques to
   traverse NATs like using Relay servers, TCP/UDP hole punching etc as
   described in [RFC5128].  For P2P applications to work reliably across
   NATs it is expected that the NAT devices does End-point independent
   mapping and filtering.

   Peer to Peer applications are becoming very common and some real life
   examples of P2P applications are SIP used by VoIP service providers,
   instant messaging, voice and video chat, Google Talk, Apple Facetime
   and several famous gaming applications.  The notion of not supporting
   P2P applications is not just practical and NATs MUST be designed to
   facilitate these applications.

   While it is tempting to maximize the return on the investment by
   maximizing the use of the existing IPv4 addresses, doing End point
   dependent mapping, the harmful effects of this overrides any benefits
   that it offers.


5.  Issues with End-point dependent mapping and filtering

   1.  End point dependent mapping does not guarantee that the same
   External address and port will be used regardless of the destination.
   This would prevent the inbound connection from an application.

   2.  End point dependent filtering will allow inbound connections only
   if a previous flow to the same host was previously initiated from an
   internal host.  This will prevent incoming connection requests from
   an application.


6.  Acknowledgements

   Thanks to Dan Wing for providing the idea to write this document and
   reviewing it.


7.  IANA Considerations

   None






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8.  Security Considerations

   None.


9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2663]  Srisuresh, P. and M. Holdrege, "IP Network Address
              Translator (NAT) Terminology and Considerations",
              RFC 2663, August 1999.

   [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.

   [RFC6146]  Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
              NAT64: Network Address and Protocol Translation from IPv6
              Clients to IPv4 Servers", RFC 6146, April 2011.

9.2.  Informative References

   [RFC5128]  Srisuresh, P., Ford, B., and D. Kegel, "State of Peer-to-
              Peer (P2P) Communication across Network Address
              Translators (NATs)", RFC 5128, March 2008.


Author's Address

   Senthil Sivakumar
   Cisco Systems
   7100-8 Kit Creek Road
   Research Triangle Park, North Carolina  27709
   USA

   Phone: +1 919 392 5158
   Email: ssenthil@cisco.com






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