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Versions: 00 01 02 03 draft-ietf-opsawg-capwap-alt-tunnel

Network Working Group                                           R. Zhang
Internet-Draft                                             China Telecom
Intended status: Standards Track                                  Z. Cao
Expires: September 6, 2014                                       H. Deng
                                                            China Mobile
                                                           R. Pazhyannur
                                                           S. Gundavelli
                                                                   Cisco
                                                                  L. Xue
                                                                  Huawei
                                                           March 5, 2014


        Alternate Tunnel Encapsulation for Data Frames in CAPWAP
                    draft-zhang-opsawg-capwap-cds-03

Abstract

   CAPWAP defines a specification to encapsulate a station's data frames
   between the Wireless Transmission Point (WTP) and Access Controller
   (AC) using CAPWAP.  Specifically, the station's IEEE 802.11 data
   frames can be either locally bridged or tunneled to the AC.  When
   tunneled, a CAPWAP data channel is used for tunneling.  In many
   deployments it is desirable to encapsulate date frames to an entity
   different from the AC for example to an Access Router (AR).  Further,
   it may also be desirable to use different tunnel encapsulations to
   carry the stations' data frames.  This document provides a
   specification for this and refers to it as Alternate tunnel
   encapsulation.  The Alternate tunnel encapsulation allows 1) the WTP
   to tunnel non-management data frames to an endpoint different from
   the AC and 2) the WTP to tunnel using one of many known encapsulation
   types such as IP-IP, IP-GRE, CAPWAP.  The WTP may advertise support
   for Alternate tunnel encapsulation during the discovery or join
   process and AC may select one of the supported Alternate Tunnel
   encapsulation types while configuring the WTP.

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



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   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 September 6, 2014.

Copyright Notice

   Copyright (c) 2014 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
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   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.  Conventions used in this document . . . . . . . . . . . .   5
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   5
   2.  Alternate Tunnel Encapsulation  . . . . . . . . . . . . . . .   6
     2.1.  Description . . . . . . . . . . . . . . . . . . . . . . .   6
     2.2.  Supported Alternate Tunnel Encapsulations . . . . . . . .   8
     2.3.   Alternate Tunnel Encapsulations Type . . . . . . . . . .   8
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   5.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  10
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   Service Providers are deploying very large Wi-Fi deployments (ranging
   from hundreds of thousands of APs to millions of APs).  These
   networks are designed to carry traffic generated from mobile users.
   The volume in mobile user traffic is already very large (in the order
   of petabytes per day) and expected to continue growing rapidly.  As a
   result, operators are looking for solutions that can scale to meet
   the increasing demand.  One way to meet the scalability requirement
   is to split the control/management plane from the data plane.  This
   separation enables the data plane be scaled independently of the



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   control/management plane.  This document provides a description of a
   CAPWAP specification change that enables the separation of data plane
   from control plane.

   CAPWAP ([RFC5415], [RFC5416]) defines a tunnel mode that specifies
   the frame tunneling type to be used for 802.11 data frames from
   stations associated with the WLAN.  The following types are
   supported:

   o  Local Bridging: All user traffic is to be locally bridged.
   o  802.3 Tunnel: All user traffic is to be tunneled to the AC in
      802.3 format.
   o  802.11 Tunnel: All user traffic is to be tunneled to the AC in
      802.11 format.

   There are two shortcomings with currently specified tunneled modes:
   1) it does not allow the WTP to tunnel data frames to an endpoint
   different from the AC and 2) it does not allow the WTP to tunnel data
   frames using any encapsulation other than CAPWAP (as specified in
   Section 4.4.2 of [RFC5415]).  Next, we describe what is driving the
   above mentioned two requirements.

   Some operators deploying large number of Access Points prefer to
   centralize the management and control of Access Points while
   distributing the handling of data traffic to increase scaling.  This
   motivates an architecture as shown in Figure 1 that has the AC in a
   centralized location and one or more tunnel gateways (or Access
   Routers) that terminate the data tunnels from the various WTPs.  This
   split architecture has two benefits over an architecture where data
   traffic is aggregated at the AC: 1) reduces the scale requirement on
   data traffic handling capability of the AC and 2) leads to more
   efficient/optimal routing of data traffic.



















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                  Locally Bridged
               +-----+   DATA   +----------------+
               | WTP |==========|  Access Router |
               +-----+          +----------------+
                     \\
                      \\       CAPWAP            +--------+
                         ++======================+   AC   |
                        //                       +--------+
                       //
               +-----+//  DATA   +----------------+
               | WTP |===========|  Access Router |
               +=====+           +----------------+
                  Locally Bridged

            Figure 1: Centralized Control with Distributed Data

   The above system (shown in Figure 1) could be achieved by setting the
   tunnel mode to Local bridging.  In such a case the AC would handle
   control of WTPs as well as handle the management traffic to/from the
   stations.  There is CAPWAP Control and Data Channel between the WTP
   and the AC.  The CAPWAP Data channel carries the IEEE 802.11
   management traffic (like IEEE 802.11 Action Frames).  The station's
   data frames are locally bridged, i.e., not carried over the CAPWAP
   data channel.  The station's data frames are handled by the Access
   Router.  However, in many deployments the operator managing the WTPs/
   AC may be different from the operator providing the internet
   connectivity to the WTPs.  Further, the WTP operator may want (or be
   required by legal/regulatory requirements) to tunnel the traffic back
   to an Access Router in its network as shown in Figure 2.  The
   tunneling requirement may be driven by the need to apply policy at
   the Access Router or a legal requirement to support lawful intercept
   of user traffic.  What this means is that local bridging does not
   meet their requirements.  Their requriements are met either by having
   the WTP tunnel the station's traffic to the AC or the WTP support an
   alternate tunnel, i.e., a tunnel to an alternate entity different
   from the AC.  This is the motivation for Alternate Tunnel
   encapsulation support where the data tunnels from the WTP are
   terminated at an AR (and more specifically at an end point different
   from the AC).












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          Tunnel to AR _________
         +-----+      (         )              +-----------------+
         | WTP |======+Internet +==============|Access Router(AR)|
         +-----+      (_________}              +-----------------+
               \\      ________
                \\    (        ) CAPWAP        +--------+
                   ++==Internet+===============|   AC   |
                  //  (        )               +--------+
                 //  ________
         +-----+//  (         )                +----------------+
         | WTP |====+Internet +================|  Access Router |
         +=====+    (_________}                +----------------+
          Tunnel to AR

            Figure 2: Centralized Control with Distributed Data

   In the case where the WTP is tunneling data frames to an AR (and not
   the AC), the choice of tunnel encapsulation need not be restricted
   only to CAPWAP (as described in Section 4.4.2 of [RFC5415]).  In
   fact, the WTP may additionally support other widely used
   encapsulation types such as L2TP, L2TPv3, IP-in-IP, IP/GRE, etc.  The
   WTP may advertise the different alternate tunnel encapsulation types
   supported and the AC can select one of the supported encapsulation
   types.  As shown in the figure there is still a CAPWAP control and
   data channel between the WTP and AC wherein the CAPWAP data channel
   carries the stations' management traffic.  Thus the WTP will maintain
   three tunnels: CAPWAP Control, CAPWAP Data, and another (alternate)
   tunnel to the AR.  The main reason to maintain a CAPWAP data channel
   is to minimize the changes on the WTP and AC required to transport
   stations' management frames (like EAP, IEEE 802.11 Action Frames).
   These management frames are transported over the CAPWAP data channel
   as they are done for case when the WTP's tunnel mode is configured as
   the local bridging.  In this specification we describe how the WTP
   can be configured with this alternate tunnel.

1.1.  Conventions used in this document

   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]

1.2.  Terminology

   Station (STA): A device that contains an IEEE 802.11 conformant
   medium access control (MAC) and physical layer (PHY) interface to the
   wireless medium (WM).





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   Access Controller (AC): The network entity that provides WTP access
   to the network infrastructure in the data plane, control plane,
   management plane, or a combination therein.

   Wireless Termination Point (WTP), The physical or network entity that
   contains an RF antenna and wireless Physical Layer (PHY) to transmit
   and receive station traffic for wireless access networks.

   CAPWAP Control Channel: A bi-directional flow defined by the AC IP
   Address, WTP IP Address, AC control port, WTP control port, and the
   transport-layer protocol (UDP or UDP-Lite) over which CAPWAP Control
   packets are sent and received.

   CAPWAP Data Channel: A bi-directional flow defined by the AC IP
   Address, WTP IP Address, AC data port, WTP data port, and the
   transport-layer protocol (UDP or UDP-Lite) over which CAPWAP Data
   packets are sent and received.

2.  Alternate Tunnel Encapsulation

2.1.  Description






























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       +-+-+-+-+-+-+                             +-+-+-+-+-+-+
       |    WTP    |                             |    AC     |
       +-+-+-+-+-+-+                             +-+-+-+-+-+-+
             |Join Request[Supported Alternate Tunnel  |
             |       Encapsulations ]                  |
             |---------------------------------------->|
             |                                         |
             |Join Response                            |
             |<----------------------------------------|
             |                                         |
             |IEEE 802.11 WLAN Config. Request [       |
             | IEEE 802.11 Add WLAN,                   |
             | Alternate Tunnel Encapsulation (        |
             |   Tunnel Type, Tunnel Specific Info)    |
             |   ]                                     |
             |<----------------------------------------|
             |                                         |
             |IEEE 802.11 WLAN Config. Response        |
             |---------------------------------------->|
             |                                         |
             |                                         |
        +-+-+-+-+-+-+                                  |
        | Setup     |                                  |
        | Alternate |                                  |
        | Tunnel    |                                  |
        +-+-+-+-+-+-+                                  |
             |                                         |
             |WTP Event Request[Alt Tunnel Established]|
             |---------------------------------------->|
             |                                         |
             |                                         |
        +-+-+-+-+-+-+                                  |
        | Tunnel    |                                  |
        | Failure   |                                  |
        |           |                                  |
        +-+-+-+-+-+-+                                  |
             |                                         |
             |Change State Event[Tunnel Failure]       |
             |---------------------------------------->|

                    Figure 3: Setup of Alternate Tunnel

   The above example describes how the alternate tunnel encapsulation
   may be established.  When the WTP joins the AC, it should indicate
   its alternate tunnel encapsulation capability.  The AC would
   determine whether an alternate tunnel configuration is required.  If
   required, it would select an appropriate alternate tunnel
   encapsulation.  The AC provides the alternate tunnel encapsulation



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   message element that provides both the tunnel-type and tunnel
   specific information.  The tunnel specific information may contain
   configuration information to help the WTP setup the tunnel.  For
   example, the IP address of the access router that will terminate the
   WTP tunnel.  Once the WTP sets up the tunnel, the WTP may inform the
   AC about the tunnel setup.  Correspondingly, if the WTP discovers
   that the tunneled link to the AR has failed, then it may inform the
   AC.

2.2.  Supported Alternate Tunnel Encapsulations

   This message element enables a WTP to communicate its capability to
   support alternate tunnel encapsulations to the AC.  The WTP may
   commmunicate its capability during the discovery or join process.

           0               1               2               3
           0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0
          +=+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
          | Num_Tunnels   |  Tunnel_1     |  Tunnel_[2..N]..
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

            Figure 4: Supported Alternate Tunnel Encapsulations

   o  Type: TBD for Supported Tunnel Encapsulations
   o  Num_Tunnels >=1: This refers to number of profiles presnt in this
      messaage element.  There must be at least one profile.
   o  Tunnel: Each Tunnel is identified by value defined in the Tunnel
      Type field in Section 2.3

2.3.  Alternate Tunnel Encapsulations Type

   The IEEE 802.11 Alternate Tunnel Encapsulation message element allows
   the AC to select the alternate tunnel encapsulation.  This messsage
   element may be provided along with the IEEE 802.11 Add WLAN message
   element.  When the message element is present the following fields of
   the IEEE 802.11 Add WLAN element shall be set as follows: MAC mode is
   set to 0 (Local MAC) and Tunnel Mode is set to 0 (Local Bridging).


        0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
       |  Tunnel Type  | Tunnel Specific
       |               |   Information
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

              Figure 5: Alternate Tunnel Encapsulations Type

   o  Type: TBD for Alternate Tunnel Encapsulation Type



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   o  Tunnel Type: The profile is identified by a value given below

      *  0: CAPWAP data channel as described in [RFC5415][RFC5416]
      *  1: L2TP
      *  2: L2TPv3
      *  3: IP-in-IP
      *  4: IP/GRE
   o  Tunnel Specific Information: This field contains tunnel specific
      information that is used to configure the WTP with parameters
      needed for alternate tunnel setup.


       0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
      |  Length       | Data
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

                   Figure 6: Tunnel Specific Information

      *  Length:
      *  Data: The data field would contain tunnel specific information
         to assist the WTP in setting up the alternate tunnel.  For
         example if the tunnel type is CAPWAP then the data field would
         contain the following (non-exhaustive) list of parameters

         +  Access Router IPv4 address
         +  Access Router IPv6 address
         +  Tunnel DTLS Policy
         +  IEEE 802.11 Tagging Policy

         This specification only defines a generic container for such
         message elements.  We anticipate that these message elements
         (for the different protocols) will be defined in separate
         documents, potentially one for each tunneling protocols.  See
         [I-D.xue-opsawg-capwap-separation-capability] for example of
         such a specification.

3.  IANA Considerations

   To be specified in later versions

4.  Security Considerations

   To be specified in later versions.







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5.  Contributors

   This document stems from the joint work of Hong Liu, Yifan Chen,
   Chunju Shao from China Mobile Research.

6.  References

6.1.  Normative References

   [RFC5415]  Calhoun, P., Montemurro, M., and D. Stanley, "Control And
              Provisioning of Wireless Access Points (CAPWAP) Protocol
              Specification", RFC 5415, March 2009.

   [RFC5416]  Calhoun, P., Montemurro, M., and D. Stanley, "Control and
              Provisioning of Wireless Access Points (CAPWAP) Protocol
              Binding for IEEE 802.11", RFC 5416, March 2009.

6.2.  Informative References

   [I-D.xue-opsawg-capwap-separation-capability]
              Xue, L., Du, Z., Liu, D., Zhang, R., and J.
              Kaippallimalil, "Capability Announcement and AR Discovery
              in CAPWAP Control and Data Channel Separation", draft-xue-
              opsawg-capwap-separation-capability-01 (work in progress),
              October 2013.

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

Authors' Addresses

   Rong Zhang
   China Telecom
   No.109 Zhongshandadao avenue
   Guangzhou  510630
   China

   Email: zhangr@gsta.com


   Zhen Cao
   China Mobile
   Xuanwumenxi Ave. No. 32
   Beijing  100871
   China

   Phone: +86-10-52686688
   Email: zehn.cao@gmail.com, caozhen@chinamobile.com



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   Hui Deng
   China Mobile
   No.32 Xuanwumen West Street
   Beijing  100053
   China

   Email: denghui@chinamobile.com


   Rajesh S. Pazhyannur
   Cisco
   170 West Tasman Drive
   San Jose, CA 95134
   USA

   Email: rpazhyan@cisco.com


   Sri Gundavelli
   Cisco
   170 West Tasman Drive
   San Jose, CA 95134
   USA

   Email: sgundave@cisco.com


Li Xue
Huawei
No.156 Beiqing Rd. Z-park, Shi-Chuang-Ke-Ji-Shi-Fan-Yuan, HaiDian District
Beijing
China

Email: xueli@huawei.com

















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