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Versions: (draft-zhang-opsawg-capwap-cds) 00 01 02 03 04 05 06 07 08 09 10 11 12 RFC 8350

Network Working Group                                           R. Zhang
Internet-Draft                                             China Telecom
Intended status: Standards Track                                  Z. Cao
Expires: March 12, 2015                                          H. Deng
                                                            China Mobile
                                                           R. Pazhyannur
                                                           S. Gundavelli
                                                                   Cisco
                                                                  L. Xue
                                                                  Huawei
                                                       September 8, 2014


        Alternate Tunnel Encapsulation for Data Frames in CAPWAP
                 draft-ietf-opsawg-capwap-alt-tunnel-03

Abstract

   Control And Provisioning of Wireless Access Points (CAPWAP) defines a
   specification to encapsulate a station's data frames between the
   Wireless Transmission Point (WTP) and Access Controller (AC).
   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 encapsulating
   data frames to an entity other than the AC (for example to an Access
   Router (AR)) is desirable.  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 March 12, 2015.

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
   publication of this document.  Please review these documents
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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
   3.  Protocol Considerations . . . . . . . . . . . . . . . . . . .   8
     3.1.  Supported Alternate Tunnel Encapsulations . . . . . . . .   8
     3.2.   Alternate Tunnel Encapsulations Type . . . . . . . . . .   9
     3.3.   IEEE 802.11 WTP Alternate Tunnel Failure Indication  . .  10
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   6.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  12
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   Service Providers are deploying very large Wi-Fi deployments (ranging
   from hundreds of thousands of APs (referred to as WTPs in CAPWAP
   terminology) 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.



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   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 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) They do not allow the WTP to tunnel data frames to an endpoint
   different from the AC and 2) They do 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 requirements 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 when the WTP's tunnel mode is configured as 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 Info Element)     |
                    | ]                                       |
                    |<----------------------------------------|
                    |                                         |
                    |                                         |
               +-+-+-+-+-+-+                                  |
               | Setup     |                                  |
               | Alternate |                                  |
               | Tunnel    |                                  |
               +-+-+-+-+-+-+                                  |
                    |                                         |
                    |IEEE 802.11 WLAN Config. Response        |
                    |---------------------------------------->|
                    |                                         |
                    |                                         |
               +-+-+-+-+-+-+                                  |
               | Tunnel    |                                  |
               | Failure   |                                  |
               +-+-+-+-+-+-+                                  |
                    |WTP Alternate Tunnel Failure Indication  |
                    |(report failure)                         |
                    |---------------------------------------->|
                    |                                         |
               +-+-+-+-+-+-+-+                                |
               | Tunnel      |                                |
               | Established |                                |
               +-+-+-+-+-+-+-+                                |
                    |WTP Alternate Tunnel Failure Indication  |
                    |(report clearing failure)                |
                    |---------------------------------------->|
                    |                                         |

                    Figure 3: Setup of Alternate Tunnel





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   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 determines
   whether an alternate tunnel configuration is required.  If an
   appropriate alternate tunnel type is selected, then the AC provides
   the alternate tunnel encapsulation message element containing the
   tunnel type and a tunnel-specific information element.  (The tunnel-
   specific information element, for example, may contain information
   like the IP address of the tunnel termination point.)  The WTP sets
   up the alternate tunnel using the alternate tunnel encapsulation
   message element.

   When the WTP detects an alternate tunnel failure, the WTP informs the
   AC using a message element (defined in this specification), WTP
   Alternate Tunnel Fail Indication.  The message element has a status
   field that indicates whether the message denotes reporting a failure
   or the clearing of the previously reported failure.

   For the case where AC is unreachable but the tunnel end point is
   still reachable, the WTP behavior is up to the implementation.  For
   example, the WTP could either choose to tear down the tunnel or let
   the existing user's traffic continue to be tunneled.

3.  Protocol Considerations

3.1.  Supported Alternate Tunnel Encapsulations

   This message element is sent by a WTP to communicate its capability
   to support alternate tunnel encapsulations.  The message element
   contains the following fields:

           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-Type 1 |  Tunnel-Type [2..N]
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 4: Supported Alternate Tunnel Encapsulations

   o  Type: <IANA-1> for Supported Alternate Tunnel Encapsulations
   o  Length: The length in bytes is 1 + Num_Tunnels
   o  Num_Tunnels: This refers to number of tunnel types present in the
      message element.  At least one tunnel type must be present.
   o  Tunnel-Type: This is identified by value defined in Section 3.2







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3.2.  Alternate Tunnel Encapsulations Type

   This message element is sent by the AC.  This message element allows
   the AC to select the alternate tunnel encapsulation.  This message
   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).
   The message element contains the following fields


       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |      Tunnel-Type            |  Info Element Length            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Info Element
       +-+-+-+-+-+-+-+-+-+




              Figure 5: Alternate Tunnel Encapsulations Type

   o  Type: <IANA-2> for Alternate Tunnel Encapsulation Type
   o  Length: > 4
   o  Tunnel-Type: The tunnel type is specified by a 2 byte value.  This
      specification defines the values from zero (0) to five (5) as
      given below.  The remaining values are reserved for future use.

      *  0: CAPWAP.  This refers to a CAPWAP data channel described in
         [RFC5415][RFC5416].  Additional description in
         [I-D.xue-opsawg-capwap-alt-tunnel-information].
      *  1: L2TP.  This refers to tunnel encapsulation described in
         [RFC2661].
      *  2: L2TPv3.  This refers to tunnel encapsulation described in
         [RFC3931].
      *  3: IP-in-IP.  This refers to tunnel encapsulation described in
         [RFC2003].
      *  4: PMIPv6.  This refers to the tunneling encapsulation
         described in [RFC5213]
      *  5: GRE-IPv4.  This refers to GRE encapsulation with IPv4 as the
         delivery protocol as described in [RFC2784]
      *  6: GRE-IPv6.  This refers to GRE encapsulation with IPv6 as the
         delivery protocol as described in [RFC2784]
   o  Info Element: This field contains tunnel specific configuration
      parameters to enable the WTP to setup the alternate tunnel.  For




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      example if the tunnel type is CAPWAP then this field may 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-alt-tunnel-information] for example of such
      a specification.

3.3.  IEEE 802.11 WTP Alternate Tunnel Failure Indication

   The Alternate Tunnel Encapsulation message element is sent by the WTP
   to inform the AC about the status of the Alternate Tunnel.  The
   message element contains the following fields


       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Radio ID  |  WLAN ID      |    Status     |   Reserved      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



       Figure 6: IEEE 802.11 WTP Alternate Tunnel Failure Indication

   o  Type: <IANA-3> for IEEE 802.11 WTP Alternate Tunnel Failure
      Indication
   o  Length: == 4
   o  Radio ID: The Radio Identifier, whose value is between one (1) and
      31, typically refers to some interface index on the WTP.
   o  WLAN ID: An 8-bit value specifying the WLAN Identifier.  The value
      MUST be between one (1) and 16.
   o  Status: An 8-bit boolean indicating whether the radio failure is
      being reported or cleared.  A value of zero is used to clear the
      event, while a value of one is used to report the event.

4.  IANA Considerations

   This document requires the following IANA considerations.





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   o  <IANA-1>.  This specification defines the Supported Alternate
      Tunnel Encapsulations Type message element in Section 3.1.  This
      elements needs to be registered in the existing CAPWAP Message
      Element Type registry, defined in [RFC5415].  The Type value for
      this element needs to be between 1 and 1023 (see Section 15.7 in
      [RFC5415]).
   o  <IANA-2>.  This specification defines the Alternate Tunnel
      Encapsulations Type message element in Section 3.2.  This element
      needs to be registered in the existing CAPWAP Message Element Type
      registry, defined in [RFC5415].  The Type value for this element
      needs to be between 1 and 1023.
   o  <IANA-3>.  This specification defines the IEEE 802.11 WTP
      Alternate Tunnel Failure Indication message element in
      Section 3.3.  This element needs to be registered in the existing
      CAPWAP Message Element Type registry, defined in [RFC5415].  The
      Type value for this element needs to be between 1024 and 2047.
   o  Tunnel-Type: This specification defines the Alternate Tunnel
      Encapsulations Type message element.  This element contains a
      field Tunnel-Type.  The namespace for the field is 16 bits
      (0-65535)).  This specification defines values, zero (0) through
      six (6) and can be found in Section 3.2.  Future allocations of
      values in this name space are to be assigned by IANA using the
      "Specification Required" policy.  IANA needs to create a registry
      called CAPWAP Alternate Tunnel-Types.  The registry format is
      given below.

        Tunnel-Type           Type Value   Reference
        CAPWAP                0
        L2TP                  1
        L2TPv3                2
        IP-IP                 3
        PMIPv6                4
        GRE-IPv4              5
        GRE-IPv6              6

5.  Security Considerations

   This document introduces three new CAPWAP WTP message elements.
   These elements are transported within CAPWAP Control messages as the
   existing message elements.  Therefore, this document does not
   introduce any new security risks compared to [RFC5415] and [RFC5416].
   The security considerations described in [RFC5415] and [RFC5416]
   apply here as well.








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6.  Contributors

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

7.  References

7.1.  Normative References

   [RFC2003]  Perkins, C., "IP Encapsulation within IP", RFC 2003,
              October 1996.

   [RFC2661]  Townsley, W., Valencia, A., Rubens, A., Pall, G., Zorn,
              G., and B. Palter, "Layer Two Tunneling Protocol "L2TP"",
              RFC 2661, August 1999.

   [RFC2784]  Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
              Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
              March 2000.

   [RFC3931]  Lau, J., Townsley, M., and I. Goyret, "Layer Two Tunneling
              Protocol - Version 3 (L2TPv3)", RFC 3931, March 2005.

   [RFC5213]  Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K.,
              and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008.

   [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.

7.2.  Informative References

   [I-D.xue-opsawg-capwap-alt-tunnel-information]
              Liu, D., Zhang, R., Xue, L., Kaippallimalil, J.,
              Pazhyannur, R., and S. Gundavelli, "Specification
              Alternate Tunnel Information for Data Frames in WLAN",
              draft-xue-opsawg-capwap-alt-tunnel-information-00 (work in
              progress), July 2014.

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






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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


   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





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   Li Xue
   Huawei
   No.156 Beiqing Rd. Z-park, HaiDian District
   Beijing
   China

   Email: xueli@huawei.com












































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