Internet DRAFT - draft-zhang-opsawg-capwap-cds
draft-zhang-opsawg-capwap-cds
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.
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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
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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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