Opsawg Working Group R. Zhang
Internet-Draft China Telecom
Intended status: Standards Track Z. Cao
Expires: April 21, 2016 H. Deng
China Mobile
R. Pazhyannur
S. Gundavelli
Cisco
L. Xue
J. You
Huawei
October 19, 2015
Alternate Tunnel Encapsulation for Data Frames in CAPWAP
draft-ietf-opsawg-capwap-alt-tunnel-06
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/.
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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
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 April 21, 2016.
Copyright Notice
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document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions used in this document . . . . . . . . . . . . 7
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 7
2. Alternate Tunnel Encapsulation . . . . . . . . . . . . . . . 8
2.1. Description . . . . . . . . . . . . . . . . . . . . . . . 8
3. Protocol Considerations . . . . . . . . . . . . . . . . . . . 10
3.1. Supported Alternate Tunnel Encapsulations . . . . . . . . 10
3.2. Alternate Tunnel Encapsulations Type . . . . . . . . . . 11
3.3. IEEE 802.11 WTP Alternate Tunnel Failure Indication . . . 12
3.4. CAPWAP based Alternate Tunnel . . . . . . . . . . . . . . 13
3.5. PMIPv6 based Alternate Tunnel . . . . . . . . . . . . . . 13
3.6. Alternate Tunnel Information Elements . . . . . . . . . . 14
3.6.1. Access Router Information Elements . . . . . . . . . 14
3.6.2. IEEE 802.11 WLAN Configuration Response . . . . . . . 16
3.6.3. Tunnel DTLS Policy Element . . . . . . . . . . . . . 16
3.6.4. IEEE 802.11 Tagging Mode Policy Element . . . . . . . 17
3.6.5. CAPWAP Transport Protocol Element . . . . . . . . . . 18
3.6.6. GRE Key Element . . . . . . . . . . . . . . . . . . . 18
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
5. Security Considerations . . . . . . . . . . . . . . . . . . . 20
6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 20
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
7.1. Normative References . . . . . . . . . . . . . . . . . . 20
7.2. Informative References . . . . . . . . . . . . . . . . . 21
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
1. Introduction
Service Providers are deploying very large Wi-Fi deployments (ranging
from hundreds of thousands of Access Points, 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 and expected to continue
growing rapidly. As a result, operators are looking for scalable
solutions that can meet the increasing demand. The scalability
requirement can be met by splitting the control/management plane from
the data plane. This enables the data plane to scale independent of
the control/management plane. This specification provides a way to
enable such separation.
CAPWAP ([RFC5415], [RFC5416]) defines a tunnel mode that describes
how the WTP handles the data plane (user traffic). The following
types are defined:
o Local Bridging: All data frames are locally bridged.
o 802.3 Tunnel: All data frames are tunneled to the AC in 802.3
format.
o 802.11 Tunnel: All data frames are tunneled to the AC in 802.11
format.
Figure 1 describes a system with Local Bridging. The AC is in a
centralized location. The data plane is locally bridged by the WTPs
leading to a system with centralized control plane with distributed
data plane. This system has two benefits: 1) reduces the scale
requirement on data traffic handling capability of the AC and 2)
leads to more efficient/optimal routing of data traffic while
maintaining centralized control/management.
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Locally Bridged
+-----+ Data Frames +----------------+
| WTP |===============| Access Router |
+-----+ +----------------+
\\
\\ CAPWAP Control Channel +----------+
++=========================| AC |
// CAPWAP Data Channel: | |
// IEEE 802.11 Mgmt traffic +----------+
//
+-----+ +----------------+
| WTP |============== | Access Router |
+=====+ +----------------+
Locally Bridged
Data Frames
Figure 1: Centralized Control with Distributed Data
The AC handles control of WTPs. In addition, the AC also handles the
IEEE 802.11 management traffic to/ from the stations. There is
CAPWAP Control and Data Channel between the WTP and the AC. Note
that even though there is no user traffic transported between the WTP
and AC, there is still a CAPWAP Data Channel. The CAPWAP Data
channel carries the IEEE 802.11 management traffic (like IEEE 802.11
Action Frames).
Figure 2 shows a system where the tunnel mode is configured to tunnel
data frames between the WTP and the AC either using 802.3 Tunnel or
802.11 Tunnel configurations. Operators deploy this configuration
when they need to tunnel the user traffic. 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. This
requirement could be met in the locally bridged system (Figure 1) if
the access router implemented the required policy. However, in many
deployments the operator managing the WTP is different than the
operator managing the Access Router. When the operators are
different, the policy has to be enforced in a tunnel termination
point in the WTP operator's network.
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+-----+
| WTP |
+-----+
\\
\\ CAPWAP Control Channel +----------+
++=========================| AC |
// CAPWAP Data Channel: | |
// IEEE 802.11 Mgmt traffic | |
// Data Frames +----------+
//
+-----+
| WTP |
+=====+
Figure 2: Centralized Control and Centralized Data
The key difference with the locally bridged system is that the data
frames are tunneled to the AC instead of being locally bridged.
There are two shortcomings with system in Figure 2. 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]).
Figure 3 shows a system where the WTP tunnels data frames to an
alternate entity different from the AC. The WTP also uses an
alternate tunnel encapsulation such as such as L2TP, L2TPv3, IP-in-
IP, IP/GRE, etc. This enables 1) independent scaling of data plane
and 2) leveraging of commonly used tunnel encapsulations such as
L2TP, GRE, etc
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Alternate Tunnel to AR (L2TPv3, IP-IP, CAPWAP, etc)
_________
+-----+ ( ) +-----------------+
| WTP |======+Internet +==============|Access Router(AR)|
+-----+ (_________) +-----------------+
\\ ________ CAPWAP Control
\\ ( ) Channel +--------+
++==Internet+========================| AC |
// (________)CAPWAP Data Channel: +--------+
// IEEE 802.11 Mgmt traffic
// _________
+-----+ ( ) +----------------+
| WTP |====+Internet +================| Access Router |
+=====+ (_________) +----------------+
Alternate Tunnel to AR (L2TPv3, IP-IP, CAPWAP, etc)
Figure 3: Centralized Control with Alternate Tunnel for Data
The WTP may support widely used encapsulation types such as L2TP,
L2TPv3, IP-in-IP, IP/GRE, etc. The WTP advertises the different
alternate tunnel encapsulation types it can support. The AC
configures one of the advertised types. As shown in the figure there
is a CAPWAP control and data channel between the WTP and AC. The
CAPWAP data channel carries the stations' management traffic as in
the case of the locally bridged system. The main reason to maintain
a CAPWAP data channel is to maintain similarity with the locally
bridged system. The WTP maintains three tunnels: CAPWAP Control,
CAPWAP Data, and another alternate tunnel for the data frame. The
data frames are transported by an alternate tunnel between the WTP
and a tunnel termination point such as an Access Router. This
specification describes how the alternate tunnel can be established.
The specification defines message elements for the WTP to advertise
support for alternate tunnel encapsulation, the AC to configure
alternate tunnel encapsulation, and for the WTP to report failure of
the alternate tunnel.
The alternate tunnel encapsulation also supports the third-party WLAN
service provider scenario (i.e. Virtual Network Operator, VNO).
Under this scenario, the WLAN provider owns the WTP and AC resources,
while the VNOs can rent the WTP resources from the WLAN provider for
network access. The AC belonging to the WLAN service provider
manages the WTPs in the centralized mode.
As shown in Figure 4, VNO 1&2 don't possess the network access
resources, however they provide services by acquiring resources from
the WLAN provider. Since a WTP is capable of supporting up to 16
Service Set Identifiers (SSIDs), the WLAN provider may provide
network access service for different providers with different SSIDs.
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For example, SSID1 is advertised by the WTP for VNO1; while SSID2 is
advertised by the WTP for VNO2. Therefore the data traffic from the
user can be directly steered to the corresponding access router of
the VNO who owns that user.
+----+
| AC |
+--+-+
CAPWAP-CTL |
+-----------------+
| CAPWAP-DATA: IEEE 802.11 Mgmt traffic
|
WLAN Provider| VNO 1
+-----+ CAPWAP-DATA (SSID1) +---------------+
SSID1 | WTP +--------------------------|Access Router 1|
SSID2 +--+-++ +---------------+
| |
| | VNO 1
| | GRE-IPv4-DATA (SSID1) +---------------+
| +---------------------------|Access Router 2|
| +---------------+
|
| VNO 2
| CAPWAP-DATA (SSID2) +---------------+
+-----------------------------|Access Router 3|
+---------------+
Figure 4: Third-party WLAN Service Provider
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).
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.
Access Router (AR): A specialized router usually residing at the edge
or boundary of a network. This router ensures the connectivity of
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its network with external networks, a wide area network or the
Internet.
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. In certain WTP modes, the CAPWAP Data
Channel only transports IEEE 802.11 management frames and not the
data plane (user traffic).
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 (AR address(es))) |
|---------------------------------------->|
| |
+-+-+-+-+-+-+-+ |
| Tunnel | |
| Established | |
+-+-+-+-+-+-+-+ |
|WTP Alternate Tunnel Failure Indication |
|(report clearing failure) |
|---------------------------------------->|
| |
Figure 5: 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.
On detecting a tunnel failure, WTP shall forward data frames to the
AC and discard the frames. In addition, WTP may dissociate existing
clients and refuse association requests from new clients. Depending
on the implementation and deployment scenario, the AC may choose to
reconfigure the WLAN (on the WTP) to a local bridging mode or to
tunnel frames to the AC. When the WTP detects an alternate tunnel
failure, the WTP informs the AC using a message element, WTP
Alternate Tunnel Fail Indication (defined in this specification).
The WTP also needs to notify the AC of which AR(s) are unavailable.
Particularly, in the VNO scenario, the AC of the WLAN service
provider needs to maintain the association of the AR addresses of the
VNOs and SSIDs, and provide this information to the WTP for the
purpose of load balancing or master-slave mode.
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 alternate
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:
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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 6: 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
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 7: 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].
* 1: L2TP. This refers to tunnel encapsulation described in
[RFC2661].
* 2: L2TPv3. This refers to tunnel encapsulation described in
[RFC3931].
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* 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 RFC2874.
* 6: GRE-IPv6. This refers to GRE encapsulation with IPv6 as the
delivery protocol as described in RFC2874.
o Info Element: This field contains tunnel specific configuration
parameters to enable the WTP to setup the alternate tunnel. This
specification provides details for this elements for CAPWAP and
PMIPv6. We anticipate that message elements for the other
protocols (like L2TPv3, etc) will be defined in other
specifications in the future.
3.3. IEEE 802.11 WTP Alternate Tunnel Failure Indication
The Alternate Tunnel Failure Indication message element is sent by
the WTP to inform the AC about the status of the Alternate Tunnel.
For the case where WTP establishes data tunnels with multiple ARs
(e.g., under VNO scenario), the WTP needs to notify the AC of which
AR(s) are unavailable. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| WLAN ID | Status | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. Access Router Information Element .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: 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 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.
o Access Router Information Element: IPv4 address or IPv6 address or
Fully Qualified Domain Name (FQDN), of the Access Router for the
alternate tunnel. The Access Router Information Elements allow
the WTP to notify the AC of which AR(s) are unavailable.
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3.4. CAPWAP based Alternate Tunnel
If the CAPWAP encapsulation is selected by the AC and configured by
the AC to the WTP, the Info Element field defined in Section 3.2
should contain the following information:
o Access Router Information: IPv4 address or IPv6 address or Fully
Qualified Domain Name (FQDN), of the Access Router for the
alternate tunnel.
o Tunnel DTLS Policy: The CAPWAP protocol allows optional protection
of data packets using DTLS. Use of data packet protection on a
WTP is not mandatory but determined by the associated AC policy
(This is consistent with the WTP behavior described in [RFC5415]).
o IEEE 802.11 Tagging Mode Policy: It is used to specify how the
CAPWAP data channel packet are to be tagged for QoS purposes (see
[RFC5416] for more details).
o CAPWAP Transport Protocol: The CAPWAP protocol supports both UDP
and UDP-Lite (see RFC3828). When run over IPv4, UDP is used for
the CAPWAP data channels. When run over IPv6, the CAPWAP data
channel may use either UDP or UDP-lite.
The message element structure for CAPWAP encapsulation is shown in
Figure 9:
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=0 | Info Element Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. Access Router Information Element .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. Tunnel DTLS Policy Element .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. IEEE 802.11 Tagging Mode Policy Element .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. CAPWAP Transport Protocol Element .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: Alternate Tunnel Encapsulation - CAPWAP
3.5. PMIPv6 based Alternate Tunnel
Proxy Mobile IPv6 (PMIPv6) (defined in [RFC5213]) can also be used
for alternate tunnel encapsulation between the WTP and the AR. In
this scenario, a WTP acts as the Mobile Access Gateway (MAG) function
that manages the mobility-related signaling for a station that is
attached to the WTP IEEE 802.11 radio access. The Local Mobility
Anchor (LMA) function is at the AR. If PMIPv6 encapsulation is
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selected by the AC and configured by the AC to a WTP, the Info
Element field defined in Section 3.2 should contain the following
information:
o Access Router (acts as LMA) Information: IPv6 address or Fully
Qualified Domain Name (FQDN) for the alternate tunnel endpoint.
The message element structure for PMIPv6 encapsulation is shown in
Figure 10:
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=4 | Info Element Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. Access Router (LMA) Information Element .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: Alternate Tunnel Encapsulation - PMIPv6
3.6. Alternate Tunnel Information Elements
This section defines the various elements described in Section 3.4
and Section 3.5
3.6.1. Access Router Information Elements
The Access Router Information Elements allow the AC to notify a WTP
of which AR(s) are available for establishing a data tunnel. The AR
information may be IPv4 address, IPv6 address, or AR domain name. If
a WTP obtains the correct AR FQDN, the Name-to-IP address mapping is
handled in the WTP (see RFC2782).
The following are the Access Router Information Elements defined in
this specification. The AC can use one of them to notify the
destination information of the data tunnel to the WTP. The Elements
containing the AR IPv4 address MUST NOT be used if an IPv6 data
channel such as PMIPv6 or GREv6 is used.
3.6.1.1. AR IPv4 List Element
This Element (see Figure 11) is used by the AC to configure a WTP
with the AR IPv4 address available for the WTP to establish the data
tunnel for user traffic.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AR IPv4 Element Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. AR IPv4 Address-1 .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. AR IPv4 Address-2 .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. AR IPv4 Address-N .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11: AR IPv4 List Element
Length: This refers to the total length in octets of the element
excluding the Type and Length fields.
AR IPv4 Address: IPv4 address of the AR. At least one IPv4 address
shall be present. Multiple addresses may be provided for load
balancing or redundancy.
3.6.1.2. AR IPv6 List Element
This Element (see Figure 12) is used by the AC to configure a WTP
with the AR IPv6 address available for the WTP to establish the data
tunnel for user traffic.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AR IPv6 Element Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. AR IPv6 Address-1 .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. AR IPv6 Address-2 .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. AR IPv6 Address-N .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12: AR IPv6 List Element
Length: This refers to the total length in octets of the element
excluding the Type and Length fields.
AR IPv6 Address: IPv6 address of the AR. At least one IPv6 address
shall be present. Multiple addresses may be provided for load
balancing or redundancy.
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3.6.1.3. AR FQDN List Element
This Element (see Figure 13) is used by the AC to configure a WTP
with AR FQDN available to establish the data tunnel for user traffic.
Based on the FQDN, a WTP can acquire the AR IP address via DNS.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AR FQDN Element Type | Element Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | AR FQDN-1 .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | AR FQDN-2 .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | AR FQDN-N .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 13: AR FQDN List Element
Element Length: This refers to the total length in octets of the
element excluding the Type and element Length fields.
Length: The length of each AR FQDN.
AR FQDN: An array of variable-length string containing AR FQDN. This
can be used to satisfy load-balance and reliability requirements.
3.6.2. IEEE 802.11 WLAN Configuration Response
Since AC can configure a WTP with more than one AR available for the
WTP to establish the data tunnel(s) for user traffic, it may be
useful for the WTP to communicate the selected AR. To enable this,
the IEEE 802.11 WLAN Configuration Response may contain the AR list
element containing the selected AR.
3.6.3. Tunnel DTLS Policy Element
The AC distributes its DTLS usage policy for the CAPWAP data tunnel
between a WTP and the AR. There are multiple supported options,
represented by the bit field below as defined in AC Descriptor
message elements. The WTP MUST abide by one of the options for
tunneling user traffic with AR. The Tunnel DTLS Policy Element obey
the definition in [RFC5415]. If there are more than one ARs
information provided by the AC for reliability reasons, the same
Tunnel DTLS Policy (see Figure 14) is generally applied for all
tunnels associated with the ARs. Otherwise, Tunnel DTLS Policy MUST
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be bonding together with each of the ARs, then WTP will enforce the
independent tunnel DTLS policy for each tunnel with a specific AR.
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 DTLS Element Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |A|D|C|R|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. AR Information (optional) .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 14: Tunnel DTLS Policy Element
Reserved: A set of reserved bits for future use. All implementations
complying with this protocol MUST set to zero any bits that are
reserved in the version of the protocol supported by that
implementation. Receivers MUST ignore all bits not defined for the
version of the protocol they support.
A: If A bit is set, there is an AR information associated with the
DTLS policy. There may be an array of pairs binding DTLS policy
information and AR information contained in the Tunnel DTLS Policy
Element. Otherwise, the same Tunnel DTLS Policy (see Figure 14) is
generally applied for all tunnels associated with the ARs configured
by the AC.
D: DTLS-Enabled Data Channel Supported (see [RFC5415]).
C: Clear Text Data Channel Supported (see [RFC5415]).
R: A reserved bit for future use abide (see [RFC5415]).
3.6.4. IEEE 802.11 Tagging Mode Policy Element
In 802.11 networks, IEEE 802.11 Tagging Mode Policy Element is used
to specify how the WTP apply the QoS tagging policy when receiving
the packets from stations on a particular radio. When the WTP sends
out the packet to data channel to the AR(s), the packets have to be
tagged for QoS purposes (see [RFC5416]).
The IEEE 802.11 Tagging Mode Policy abides the IEEE 802.11 WTP
Quality of Service defined in Section 6.22 of [RFC5416].
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3.6.5. CAPWAP Transport Protocol Element
The CAPWAP data tunnel supports both UDP and UDP-Lite (see RFC3828).
When run over IPv4, UDP is used for the CAPWAP data channels. When
run over IPv6, the CAPWAP data channel may use either UDP or UDP-
lite. The AC specifies and configure the WTP for which transport
protocol is to be used for the CAPWAP data tunnel.
The CAPWAP Transport Protocol Element abides the definition in
Section 4.6.14 of [RFC5415].
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=51 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Transport |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 15: CAPWAP Transport Protocol Element
Type: 51 for CAPWAP Transport Protocol [RFC5415].
Length: 1
Transport: The transport to use for the CAPWAP Data channel. The
following enumerated values are supported:
1 - UDP-Lite: The UDP-Lite transport protocol is to be used for the
CAPWAP Data channel. Note that this option MUST NOT be used if the
CAPWAP Control channel is being used over IPv4 and AR address is IPv4
contained in the AR Information Element.
2 - UDP: The UDP transport protocol is to be used for the CAPWAP Data
channel.
3.6.6. GRE Key Element
If a WTP receives the GRE Key Element in the Alternate Tunnel
Encapsulation message element for GREv4 or GREv6 selection, the WTP
must insert the GRE Key to the encapsulation packet (see [RFC2890]).
An AR acting as decapsulating tunnel endpoint identifies packets
belonging to a traffic flow based on the Key value.
The GRE Key Element field contains a four octet number defined in
[RFC2890].
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GRE Key Element Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GRE Key |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 16: GRE Key Element
GRE Key: The Key field contains a four octet number which is inserted
by the WTP according to [RFC2890].
4. IANA Considerations
This document requires the following IANA considerations.
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.
o AR IPv4 Element Type: AR IPv4 List Element (see Figure 11) is used
by the AC to configure a WTP with the AR IPv4 address available
for the WTP to establish the data tunnel for user traffic.
o AR IPv6 Element Type: AR IPv6 List Element (see Figure 12) is used
by the AC to configure a WTP with the AR IPv6 address available
for the WTP to establish the data tunnel for user traffic.
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o AR FQDN Element Type: AR FQDN Element (see Figure 13) is used by
the AC to configure a WTP with AR FQDN available to establish the
data tunnel for user traffic.
o Tunnel DTLS Element Type: The Tunnel DTLS Policy Element obey the
definition in [RFC5415].
o GRE Key Element Type: If a WTP receives the GRE Key Element in the
Alternate Tunnel Encapsulation message element for GREv4 or GREv6
selection, the WTP must insert the GRE Key to the encapsulation
packet
Tunnel-Type Type Value Reference
CAPWAP 0 [RFC5415],[RFC5416]
L2TP 1 [RFC2661]
L2TPv3 2 [RFC3931]
IP-IP 3 [RFC2003]
PMIPv6 4 [RFC5213]
GRE-IPv4 5 [RFC2784]
GRE-IPv6 6 [RFC2784]
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].
In CAPWAP, security for CAPWAP Data Channel is optional and security
policy is determined by AC. Similarly, the AC determines the
security for the Alternate Tunnel between WTP and Alternate Tunnel
Encapsulation Gateway. The security considerations described in
[RFC5415] and [RFC5416] apply here as well.
6. Contributors
This document stems from the joint work of Hong Liu, Yifan Chen,
Chunju Shao from China Mobile Research. The authors would like to
thank Zongpeng Du and Jin Li for their valuable comments.
7. References
7.1. Normative References
[RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, DOI
10.17487/RFC2003, October 1996,
<http://www.rfc-editor.org/info/rfc2003>.
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[RFC2661] Townsley, W., Valencia, A., Rubens, A., Pall, G., Zorn,
G., and B. Palter, "Layer Two Tunneling Protocol "L2TP"",
RFC 2661, DOI 10.17487/RFC2661, August 1999,
<http://www.rfc-editor.org/info/rfc2661>.
[RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
DOI 10.17487/RFC2784, March 2000,
<http://www.rfc-editor.org/info/rfc2784>.
[RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE",
RFC 2890, DOI 10.17487/RFC2890, September 2000,
<http://www.rfc-editor.org/info/rfc2890>.
[RFC3828] Larzon, L-A., Degermark, M., Pink, S., Jonsson, L-E., Ed.,
and G. Fairhurst, Ed., "The Lightweight User Datagram
Protocol (UDP-Lite)", RFC 3828, DOI 10.17487/RFC3828, July
2004, <http://www.rfc-editor.org/info/rfc3828>.
[RFC3931] Lau, J., Ed., Townsley, M., Ed., and I. Goyret, Ed.,
"Layer Two Tunneling Protocol - Version 3 (L2TPv3)", RFC
3931, DOI 10.17487/RFC3931, March 2005,
<http://www.rfc-editor.org/info/rfc3931>.
[RFC5213] Gundavelli, S., Ed., Leung, K., Devarapalli, V.,
Chowdhury, K., and B. Patil, "Proxy Mobile IPv6", RFC
5213, DOI 10.17487/RFC5213, August 2008,
<http://www.rfc-editor.org/info/rfc5213>.
[RFC5415] Calhoun, P., Ed., Montemurro, M., Ed., and D. Stanley,
Ed., "Control And Provisioning of Wireless Access Points
(CAPWAP) Protocol Specification", RFC 5415, DOI 10.17487/
RFC5415, March 2009,
<http://www.rfc-editor.org/info/rfc5415>.
[RFC5416] Calhoun, P., Ed., Montemurro, M., Ed., and D. Stanley,
Ed., "Control and Provisioning of Wireless Access Points
(CAPWAP) Protocol Binding for IEEE 802.11", RFC 5416, DOI
10.17487/RFC5416, March 2009,
<http://www.rfc-editor.org/info/rfc5416>.
7.2. Informative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
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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: zhen.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
Jianjie You
Huawei
101 Software Avenue, Yuhuatai District
Nanjing, 210012
China
Email: youjianjie@huawei.com
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