Optimizing NAT and Firewall Keepalives Using Port Control Protocol (PCP)
draft-reddy-pcp-optimize-keepalives-00

PCP                                                             T. Reddy
Internet-Draft                                                     Cisco
Intended status: Standards Track                              M. Isomaki
Expires: March 20, 2013                                            Nokia
                                                                 D. Wing
                                                                P. Patil
                                                                   Cisco
                                                      September 16, 2012

Optimizing NAT and Firewall Keepalives Using Port Control Protocol (PCP)
                 draft-reddy-pcp-optimize-keepalives-00

Abstract

   This document describes how Port Control Protocol is useful to reduce
   NAT and firewall keepalive messages for a variety of applications.

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
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   This Internet-Draft will expire on March 20, 2013.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   the Trust Legal Provisions and are provided without warranty as

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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Notational Conventions . . . . . . . . . . . . . . . . . . . .  3
   3.  Overview of Operation  . . . . . . . . . . . . . . . . . . . .  3
     3.1.  Application Scenarios  . . . . . . . . . . . . . . . . . .  3
     3.2.  NAT and Firewall Topologies and Detection  . . . . . . . .  5
     3.3.  Keepalive Optimization . . . . . . . . . . . . . . . . . .  6
   4.  Application-Specific Operation . . . . . . . . . . . . . . . .  6
     4.1.  SIP  . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
     4.2.  HTTP . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
     4.3.  Media and data channels with ICE . . . . . . . . . . . . .  8
     4.4.  Detecting Flow Failure . . . . . . . . . . . . . . . . . .  9
     4.5.  Firewall . . . . . . . . . . . . . . . . . . . . . . . . .  9
       4.5.1.  IPv6 Network with Firewalls  . . . . . . . . . . . . .  9
       4.5.2.  Mobile Network with Firewalls  . . . . . . . . . . . .  9
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 10
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 11
   Appendix A.  Example PHP script  . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11

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1.  Introduction

   Many types of applications need to keep their Network Address
   Translator (NAT) and Firewall (FW) mappings alive for long periods of
   time, even when they are otherwise not sending or receiving any
   traffic.  This is typically done by sending periodic keep-alive
   messages just to prevent the mappings from expiring.  As NAT/FW
   mapping timers may be short and unknown to the endpoint, the
   frequency of these keep-alives may be high.  An IPv4 or IPv6 host can
   use the Port Control Protocol (PCP)[I-D.ietf-pcp-base] to flexibly
   manage the IP address and port mapping information on NATs and FWs to
   facilitate communications with remote hosts.  This document describes
   how PCP can be used to reduce keep-alive messages for both client-
   server and peer-to-peer type of communication.

   The mechanism described in this document is especially useful in
   cellular mobile networks, where frequent keep-alive messages make the
   radio transition between active and power-save states causing
   signaling congestion.  The excessive time spent on the active state
   due to keep-alives also greatly reduces the battery life of the
   cellular connected devices such as smartphones or tablets.

2.  Notational Conventions

   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].

   This note uses terminology defined in [RFC5245] and
   [I-D.ietf-pcp-base] .

3.  Overview of Operation

3.1.  Application Scenarios

   PCP can help both client-server and peer-to-peer applications to
   reduce their keep-alive rate.  The relevant applications are the ones
   that need to keep their NAT/FW mappings alive for long periods of
   time, for instance to be able to send or receive application messages
   to both directions at any time.

   A typical client-server scenario is described in Figure 1.  A client,
   who may reside behind one or multiple layers of NATs/FWs, opens a
   connection to a globally reachable server, and keeps it open to be
   able to receive messages from the server at any time.  The connection
   may be a real transport connection using TCP or SCTP, or just an flow

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   of UDP packets.  Protocols operating in this manner include Session
   Initiation Protocol (SIP), Extensible Messaging and Presence Protocol
   (XMPP), Internet Mail Application Protocol (IMAP) with its IDLE
   command, the WebSocket protocol and the various HTTP long-polling
   protocols.  There are also a number of proprietary instant messaging,
   Voice over IP, e-mail and notification delivery protocols that belong
   in this category.  All of these protocols aim to keep the client-
   server connection alive for as long as the application is running.
   When the application has otherwise no traffic to send, specific keep-
   alive messages are sent periodically to ensure that the NAT/FW state
   in the middle does not expire.  Instead of application keep-alives,
   the client can use PCP to keep up the required mapping at the NAT/FW.

        PCP          PCP
       Client       Server      __________
   +-----------+   +------+    /          \   +-----------+
   |Application|___| NAT/ |____| Internet |___|Application|
   |  Client   |   |  FW  |    |          |   |   Server  |
   +-----------+   +------+    \__________/   +-----------+
                  (multiple
                   layers)

          ------------> PCP

          ----------------------------------------->
                  Application keep-alive

               Figure 1: PCP with Client-Server applications

   There are also scenarios where the long-term communication
   association is between two peers, both of whom may reside behind a
   (layers of) NAT/FW.  This is depicted in Figure 2.  The initiation of
   the association may have happened using mechanisms such as
   Interactive Communications Establishment (ICE), perhaps first
   triggered by a "signaling" protocol such as SIP or XMPP or RTCWeb.
   Examples of the peer-to-peer protocols include RTP and RTCWeb data
   channel.  A number of proprietary VoIP or video call or streaming or
   file transfer protocols also exist in this category.  Typically the
   communication is based on UDP, but TCP or SCTP may be used.  Unless
   there is no traffic flowing otherwise, the peers have to inject
   periodic keep-alive packets to keep the NAT/FW mappings on both sides
   of the communication active.  Instead of application keep-alives,
   both peers can use PCP to control the mappings on the NAT/FWs in
   front of them.

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        PCP          PCP                        PCP          PCP
       Client       Server      __________     Server       Client
   +-----------+   +------+    /          \   +------+   +-----------+
   |Application|___| NAT/ |____| Internet |___| NAT/ |___|Application|
   |   Peer    |   |  FW  |    |          |   |  FW  |   |    Peer   |
   +-----------+   +------+    \__________/   +------+   +-----------+
                  (multiple                  (multiple
                   layers)                    layers)

          ------------> PCP                   PCP <------------

          <--------------------------------------------------->
                          Application keep-alive

               Figure 2: PCP with Peer-to-Peer applications

3.2.  NAT and Firewall Topologies and Detection

   Before an application can reduce its keep-alive rate, it has to make
   sure it has all of the NATs and Firewalls on its path under control.
   This means it has to detect the presence of any PCP-unaware NATs and
   Firewalls on its path.  PCP itself is able to detect unexpected NATs
   between the PCP client and server as depicted in Figure 3.  The PCP
   client includes its own IP address and UDP port within the PCP
   request.  The PCP server compares them to the source IP address and
   UDP port it sees on the packet.  If they are differ, there are one or
   more additional NATs between the PCP client and server, and the
   server will return an error.  Unless the application has some other
   means to control these PCP unaware NATs, it has to fall back to its
   default keep-alive mechanism.

        PCP           PCP       PCP
       Client       Unaware    Aware       __________
   +-----------+   +------+   +------+    /          \   +-----------+
   |Application|___| NAT  |___| NAT/ |____| Internet |___|Application|
   |  Client   |   |      |   |  FW  |    |          |   |   Server  |
   +-----------+   +------+   +------+    \__________/   +-----------+

         <-----------///---------->
             PCP based detection

          Figure 3: PCP unaware NAT between PCP client and server

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   Figure 4 shows a topology where one or more PCP unaware NATs are
   deployed on the exterior of the PCP capable NAT/FWs.  To detect this,
   the application must have the capability to request from its server
   or peer what IP and transport address it sees.  If those differ from
   the IP and transport address given to the application by the out most
   PCP aware NAT/FW, the application can detect that there is at least
   one more PCP unaware NAT on the path.  In this case, the application
   has to fall back to its default keep-alive mechanism.

        PCP          PCP        PCP
       Client       Aware     Unaware      __________
   +-----------+   +------+   +------+    /          \   +-----------+
   |Application|___| NAT/ |___| NAT  |____| Internet |___|Application|
   |  Client   |   |  FW  |   |      |    |          |   |   Server  |
   +-----------+   +------+   +------+    \__________/   +-----------+

         <------------>
               PCP

         <---------------------///--------------------------->
                    Application based detection

       Figure 4: PCP unaware NAT external to the last PCP aware NAT

   Section 4 describes how the detection works in a number of real
   application protocols.

   The caveat is that Firewalls can not be detected this way.

3.3.  Keepalive Optimization

   If the application determines that all NATs and Firewalls on its path
   support PCP, it can start using PCP instead of its default keep-
   alives to maintain the NAT/FW state.  It can use PCP PEER Request
   with Requested Lifetime set to appropriate value.  The application
   may still send some application specific heartbeat messages end-to-
   end.

4.  Application-Specific Operation

   This section describes how PCP is used with specific application
   protocols.

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4.1.  SIP

   For connection-less transports the User Agent (UA) sends STUN Binding
   Request over the SIP flow as described in section 4.4.2 of [RFC5626].
   The UA then learns External IP Address and Port using PEER request/
   response.  If the XOR-MAPPED-ADDRESS in the STUN Binding Response
   matches the external address and port provided by PCP PEER response
   then the UA optimizes the keepalive traffic as described in
   Section 3.3.  There is no further need to send STUN Binding Requests
   over the SIP flow to keep the NAT binding alive.

   If the XOR-MAPPED-ADDRESS in the STUN Binding Response does not match
   the external address and port provided by PCP PEER response then PCP
   will not be used to keep the NAT bindings alive for the flow that is
   being used for the SIP traffic.  This means that multiple layers of
   NAT are involved and intermediate NATs are not PCP aware.  In this
   case UA will continue to use the technique in section 4.4.2 of
   [RFC5626].

   For connection-oriented transport, the UA sends STUN Binding Request
   multiplexed with SIP over the TCP connection.  STUN multiplexed with
   other data over a TCP or TLS-over-TCP connection is explained in
   section 7.2.2 of [RFC5389].  UA then learns the External IP address
   and port using PEER request/response.  If the XOR-MAPPED-ADDRESS in
   the STUN Binding Response matches the external address and port
   provided by PCP PEER response then the UA optimizes the keepalive
   traffic as described in Section 3.3.

   If the XOR-MAPPED-ADDRESS in the STUN Binding Response does not match
   the external address and port provided by PCP PEER response then PCP
   will not be used to keep the NAT bindings alive.  In this case UA
   performs keep-alive check by sending a double-CRLF (the "ping") then
   waits to receive a single CRLF (the "pong") using the technique in
   section 4.4.1 of [RFC5626].

4.2.  HTTP

   Web Applications that require persistent connections use techniques
   such as HTTP long polling and Websockets for session keep alive as
   explained in section 3.1 of [I-D.isomaki-rtcweb-mobile].  In such
   scenarios, after the client establishes a connection with the HTTP
   server, it can execute server side scripts such as PHP residing on
   the server to provide the transport address and port of the HTTP
   client seen at the HTTP server.  In addition, the HTTP client also
   learns the external IP Address and port using PCP PEER request/
   response.

   If the IP address and port learned from the server matches the

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   external address and port provided by PCP PEER response then the HTTP
   client optimizes keepalive traffic as described in Section 3.3.

   If the IP address and port do not match then PCP will not be used to
   keep the NAT bindings alive for the flow that is being used for the
   HTTP traffic.  This means that there are NATs between the PCP server
   and the HTTP server.  The HTTP client will have to resort to use
   existing techniques for keep alive.

   Please see Appendix A for an example server side PHP script to obtain
   client source IP address.

4.3.  Media and data channels with ICE

   ICE agent learns the External IP Address and Port using MAP request/
   response.  This candidate learnt through PCP is encoded in the ICE
   offer and answer just like the server reflexive candidate, If the
   server reflexive candidate and External IP address learnt using PCP
   are different.  When using the Recommended Formula in section 4.1.2.1
   of [RFC5245] to compute priority for the candidates learnt through
   PCP, ICE agent can use preference value greater than or equal to the
   server reflexive candidates.

   The ICE agent in addition to ICE connectivity checks and performs the
   following :

   The ICE agent checks if the XOR-MAPPED-ADDRESS from the STUN
   [RFC5389] Binding response received as part of ICE connectivity check
   matches the external address and port provided by PCP MAP response.

   1.  If the match is successful then PCP will be used to keep the NAT
       bindings alive.  The ICE agent optimizes keepalive traffic by
       refreshing the mapping via new PCP MAP request containing
       information from the earlier PCP response.

   2.  If the match is not successful then PCP will not be used for keep
       NAT binding alive.  ICE agent will use technique in section 4..4
       of [RFC6263] to keep NAT bindings alive.  This means that
       multiple layers of NAT are involved and intermediate NATs are not
       PCP aware.

   Some network operators deploying a PCP Server may allow PEER but not
   MAP.  In such cases the ICE agent learns the external IP address and
   port using STUN binding request/response during ICE connectivity
   checks.  The ICE agent also learns the external IP Address and port
   using PCP PEER request/response.  If the IP address and port learned
   from STUN binding response matches the external address and port
   provided by PCP PEER response then the ICE agent optimizes keepalive

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   traffic as described in Section 3.3.

4.4.  Detecting Flow Failure

   Using the Rapid Recovery technique in section 14 of
   [I-D.ietf-pcp-base] PCP client upon receiving PCP ANNOUNCE from NAT
   device becomes aware that NAT has rebooted or lost its mapping state.
   PCP client issues new PCP requests to recreate any lost mapping state
   and thus reconstruct lost mapping fast enough that existing media,
   HTTP and SIP flows do not break.  If the NAT state cannot be
   recovered the endpoint will find the new external address and port as
   part of Rapid Recovery technique in PCP itself and reestablish
   connection with the peer.

   In lieu of this mechanism if NAT reboots and loses its mapping state
   or when a NAT gateway has its external IP address changed so that its
   current mapping state becomes invalid, it may take several seconds
   before the endpoints realize that the connectivity is lost.

4.5.  Firewall

   PCP allows applications to communicate with Firewall devices with PCP
   functionality to create mappings for incoming connections.  In such
   cases PCP can be used by the endpoint to create explicit mapping on
   Firewall to permit inbound traffic and further use PCP to avoid
   sending keep-alives to keep the Firewall mappings alive.

4.5.1.  IPv6 Network with Firewalls

   As part of the call setup, the endpoint would gather its host
   candidates and relayed candidate from a TURN server, send the
   candidates in the offer to the peer endpoint.  On receiving the
   answer from the peer endpoint, PCP client sends PCP MAP request to
   create dynamic mapping in Firewall to permit ICE connectivity checks
   and subsequent media traffic from remote peer.

4.5.2.  Mobile Network with Firewalls

   Mobile Networks are also making use of a Firewall to protect their
   customers from various attacks like downloading malicious content.
   The Firewall is usually configured to block all unknown inbound
   connections as explained in section 2.1 of
   [I-D.chen-pcp-mobile-deployment] .  In such cases PCP can be used by
   Mobile devices to create explicit mapping on Firewall to permit
   inbound traffic and optimize the keepalive traffic as described in
   Section 3.3.  This would result in saving of radio and power
   consumption of the Mobile device while protecting it from attacks.

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5.  IANA Considerations

   None

6.  Security Considerations

   Security considerations in [RFC5245]and [I-D.ietf-pcp-base] apply to
   this use.

7.  Acknowledgements

   The authors would like to thank Basavaraj Patil for valuable input to
   the document.

8.  References

8.1.  Normative References

   [I-D.ietf-pcp-base]
              Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
              Selkirk, "Port Control Protocol (PCP)",
              draft-ietf-pcp-base-26 (work in progress), June 2012.

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

   [RFC5245]  Rosenberg, J., "Interactive Connectivity Establishment
              (ICE): A Protocol for Network Address Translator (NAT)
              Traversal for Offer/Answer Protocols", RFC 5245,
              April 2010.

   [RFC5389]  Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
              "Session Traversal Utilities for NAT (STUN)", RFC 5389,
              October 2008.

   [RFC5626]  Jennings, C., Mahy, R., and F. Audet, "Managing Client-
              Initiated Connections in the Session Initiation Protocol
              (SIP)", RFC 5626, October 2009.

   [RFC6263]  Marjou, X. and A. Sollaud, "Application Mechanism for
              Keeping Alive the NAT Mappings Associated with RTP / RTP
              Control Protocol (RTCP) Flows", RFC 6263, June 2011.

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8.2.  Informative References

   [I-D.chen-pcp-mobile-deployment]
              Chen, G., Cao, Z., Boucadair, M., Ales, V., and L.
              Thiebaut, "Analysis of Port Control Protocol in Mobile
              Network", draft-chen-pcp-mobile-deployment-01 (work in
              progress), July 2012.

   [I-D.isomaki-rtcweb-mobile]
              Isomaki, M., "RTCweb Considerations for Mobile Devices",
              draft-isomaki-rtcweb-mobile-00 (work in progress),
              July 2012.

Appendix A.  Example PHP script
<html>
Connected to <?PHP echo gethostname(); ?> on port <?PHP echo
getenv(SERVER_PORT) ?> on <?PHP echo date("d-M-Y H:i:s"); ?> Pacific Time
<p>
Your IP address is: <?PHP echo getenv(REMOTE_ADDR); ?>,
port <?PHP echo getenv(REMOTE_PORT); ?>

<?PHP if (getenv(SERVER_PORT) == 80) {
??echo "<p>Click <a href=\"http://";
??echo getenv(SERVER_NAME);
??echo ":81\">here</a> to also obtain information when connecting to port
81.</p>";
??}
?>

Authors' Addresses

   Tirumaleswar Reddy
   Cisco Systems, Inc.
   Cessna Business Park, Varthur Hobli
   Sarjapur Marathalli Outer Ring Road
   Bangalore, Karnataka  560103
   India

   Email: tireddy@cisco.com

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   Markus Isomaki
   Nokia
   Keilalahdentie 2-4
   FI-02150 Espoo
   Finland

   Email: markus.isomaki@nokia.com

   Dan Wing
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose, California  95134
   USA

   Email: dwing@cisco.com

   Prashanth Patil
   Cisco Systems, Inc.
   Cessna Business Park, Varthur Hobli
   Sarjapur Marthalli Outer Ring Road
   Bangalore, Karnataka  560103
   India

   Email: praspati@cisco.com

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