wdiff rfc8350.original rfc8350.txt

Opsawg Working Group
Internet Engineering Task Force (IETF) R. Zhang
Internet-Draft
Request for Comments: 8350 China Telecom
Intended status:
Category: Experimental R. Pazhyannur
Expires: August 2, 2018
ISSN: 2070-1721 S. Gundavelli
Cisco
Z. Cao
H. Deng
Z. Du
Huawei
January 29,
April 2018

Alternate Tunnel Encapsulation for Data Frames in CAPWAP
draft-ietf-opsawg-capwap-alt-tunnel-12
Control and Provisioning of Wireless Access Points (CAPWAP)

Abstract

Control and Provisioning of Wireless Access Points (CAPWAP) defines is a
specification to encapsulate
protocol for encapsulating 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 Data
Channel is used for tunneling. In many deployments deployments, encapsulating
data frames to an entity other than the AC (for example example, to an Access
Router (AR)) is desirable. Furthermore, it may also be desirable to
use different tunnel encapsulation modes between the WTP and the
Access Router. This document defines an extension to the CAPWAP
protocol
for supporting that supports this capability 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 types, such as IP-IP, IP-GRE, or CAPWAP. The WTP may
advertise support for alternate tunnel encapsulation during the
discovery and join
process process, and the AC may select one of the
supported alternate tunnel encapsulation types while configuring the
WTP.

Status of This Memo

This Internet-Draft document is submitted in full conformance with the
provisions of BCP 78 not an Internet Standards Track specification; it is
published for examination, experimental implementation, and BCP 79.

Internet-Drafts are working documents
evaluation.

This document defines an Experimental Protocol for the Internet
community. This document is a product of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list It represents the consensus of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft the IETF
community. It has received public review and has been approved for
publication by the Internet Engineering Steering Group (IESG). Not
all documents valid approved by the IESG are candidates for a maximum any level of
Internet Standard; see Section 2 of six months RFC 7841.

Information about the current status of this document, any errata,
and how to provide feedback on it may be updated, replaced, or obsoleted by other documents obtained 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 August 2, 2018.
https://www.rfc-editor.org/info/rfc8350.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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described in the Simplified BSD License.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions used Used in this document This Document . . . . . . . . . . . . 7
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 7
1.3. History of the document Document . . . . . . . . . . . . . . . . . 8
2. Alternate Tunnel Encapsulation Overview . . . . . . . . . . . 8
3. Extensions for CAPWAP Protocol Message Elements Extensions . . . . . . . . . 11
3.1. Supported Alternate Tunnel Encapsulations . . . . . . . . 11
3.2. Alternate Tunnel Encapsulations Type . . . . . . . . . . 11
3.3. IEEE 802.11 WTP Alternate Tunnel Failure Indication . . . 12
4. Alternate Tunnel Types . . . . . . . . . . . . . . . . . . . 13
4.1. CAPWAP based CAPWAP-Based Alternate Tunnel . . . . . . . . . . . . . . 13
4.2. PMIPv6 based PMIPv6-Based Alternate Tunnel . . . . . . . . . . . . . . 14
4.3. GRE based GRE-Based Alternate Tunnel . . . . . . . . . . . . . . . 15
5. Alternate Tunnel Information Elements . . . . . . . . . . . . 15
5.1. Access Router Information Elements . . . . . . . . . . . 15 16
5.1.1. AR IPv4 List Element . . . . . . . . . . . . . . . . 16
5.1.2. AR IPv6 List Element . . . . . . . . . . . . . . . . 16 17
5.2. Tunnel DTLS Policy Element . . . . . . . . . . . . . . . 17
5.3. IEEE 802.11 Tagging Mode Policy Element . . . . . . . . . 19
5.4. CAPWAP Transport Protocol Element . . . . . . . . . . . . 20
5.5. GRE Key Element . . . . . . . . . . . . . . . . . . . . . 22
5.6. IPv6 MTU Element . . . . . . . . . . . . . . . . . . . . 23
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23
7. Security Considerations . . . . . . . . . . . . . . . . . . . 25
8. Contributors References . . . . . . . . . . . . . . . . . . . . . . . . . 25
9.
8.1. Normative References . . . . . . . . . . . . . . . . . . 25
8.2. Informative References . . . . . . . 25
9.1. Normative References . . . . . . . . . . 26
Contributors . . . . . . . . 25
9.2. Informative References . . . . . . . . . . . . . . . . . 26 . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27

1. Introduction

Service Providers are deploying very large Wi-Fi network networks containing
hundreds of thousands of Access Points (APs), which are referred to
as Wireless Transmission Points (WTPs) in Control and Provisioning of
Wireless Access Points (CAPWAP) terminology [RFC5415]. 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]) [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 IEEE 802.3 Tunnel: All data frames are tunneled to the Access
Controller (AC) in IEEE 802.3 format.

o IEEE 802.11 Tunnel: All data frames are tunneled to the AC in IEEE
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 WTPs;
this leads to a system with a centralized control plane with and a
distributed data plane. This system has two benefits: 1) it reduces
the scale requirement on the data traffic handling capability of the AC
AC, and 2) it leads to more efficient/optimal routing of data traffic
while maintaining centralized control/management.

Locally Bridged
+-----+ Data Frames +----------------+
| WTP |===============| Access Router |
+-----+ +----------------+
\\
\\ CAPWAP Control Channel +----------+
++=========================| AC |
// CAPWAP Data Channel: | |
// IEEE 802.11 Mgmt traffic 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 a
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 either the IEEE 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 AC. This requirement could be met in the locally bridged system
(Figure 1) if the Access Router (AR) implemented the required policy.
However, in many deployments 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.

+-----+
| WTP |
+-----+
\\
\\ CAPWAP Control Channel +----------+
++=========================| AC |
// CAPWAP Data Channel: | |
// IEEE 802.11 Mgmt traffic 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 the system in Figure 2. 2: 1) They do it does
not allow the WTP to tunnel data frames to an endpoint different from
the AC AC, and 2) They do 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]).

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 L2TP, Layer 2 Tunneling Protocol
(L2TP), L2TPv3, IP-in-IP, IP/
GRE, IP/GRE, etc. This enables 1) independent
scaling of data plane and 2) leveraging of commonly used tunnel
encapsulations such as L2TP, GRE, etc.

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 Traffic
// _________
+-----+ ( ) +----------------+
| WTP |====+Internet +================| Access Router |
+-----+ (_________) +----------------+
Alternate Tunnel to AR (L2TPv3, IP-in-IP, CAPWAP, etc.)

Figure 3: Centralized Control with an 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 is shown in the figure Figure 3,
there is a CAPWAP control Control and data channel Data Channel between the WTP and AC.
The CAPWAP data channel Data Channel carries the stations' management traffic traffic, as
in the case of the locally bridged system. The main reason to
maintain a CAPWAP data channel 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
frames. The data frames are transported by an alternate tunnel
between the WTP and a tunnel termination point 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, for 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. (i.e., Virtual Network Operator, VNO). Operator (VNO)).
Under this scenario, the WLAN provider owns the WTP and AC resources, 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 1 and VNO 2 don't possess the network
access
resources, however 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. For example, SSID1 is advertised by the WTP
for VNO1; while VNO 1 while SSID2 is advertised by the WTP for VNO2. Therefore VNO 2. Therefore,
the data traffic from the user can be directly steered to the
corresponding access router Access Router of the VNO who owns that user. As is
shown in Figure 4, AC can notify multiple AR addresses for load
balancing or redundancy.

+----+
| AC |
+--+-+
CAPWAP-CTL |
+-----------------+
| CAPWAP-DATA: IEEE 802.11 Mgmt traffic Traffic
|
WLAN Provider| VNO 1
+-----+ CAPWAP-DATA (SSID1) +---------------+
SSID1 | WTP +--------------------------|Access Router 1|
SSID2 +--+-++ +---------------+
| |
| | VNO 1
| | GRE-DATA (SSID1) +---------------+
| +---------------------------|Access Router 2|
| +---------------+
|
| VNO 2
| CAPWAP-DATA (SSID2) +---------------+
+-----------------------------|Access Router 3|
+---------------+

Figure 4: Third-party Third-Party WLAN Service Provider

1.1. Conventions used Used in this document This Document

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in [RFC2119].
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.

1.2. Terminology

Station (STA): A device that contains an IEEE 802.11 conformant
medium access control 802.11-conformant
Medium Access Control (MAC) and physical Physical layer (PHY) interface to the
wireless medium
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
its network with external networks, a wide area network network, or the
Internet.

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

CAPWAP Control Channel: A bi-directional bidirectional 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 bidirectional 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).

1.3. History of the document Document

This document was started to accommodate Service Providers' need of a
more flexible deployment mode with alternative tunnels [RFC7494].
Experiments and tests have been done for this alt-tunnel alternate tunnel
network infrastructure. However important, the deployment of
relevant technology is yet to complete. be completed. This experimental Experimental
document is intended to serve as an archival record for any future
work as to on the operational and deployment requirements.

2. Alternate Tunnel Encapsulation Overview
+-+-+-+-+-+-+ +-+-+-+-+-+-+
| WTP | | AC |
+-+-+-+-+-+-+ +-+-+-+-+-+-+
|Join Request [ Supported Alternate |
| Tunnel Encapsulations ] |
|---------------------------------------->|
| |
|Join Response |
|<----------------------------------------|
| |
|IEEE 802.11 WLAN Configuration Request [ |
| IEEE 802.11 Add WLAN, |
| Alternate Tunnel Encapsulation ( |
| Tunnel Type, Tunnel Info Element) |
| ] |
|<----------------------------------------|
| |
| |
+-+-+-+-+-+-+ |
| Setup | |
| Alternate | |
| Tunnel | |
+-+-+-+-+-+-+ |
|IEEE 802.11 WLAN Configuration Response |
|[ Alternate Tunnel Encapsulation ( |
| Tunnel Type, Tunnel Info Element) ] |
|---------------------------------------->|
| |
| |
+-+-+-+-+-+-+ |
| Tunnel | |
| Failure | |
+-+-+-+-+-+-+ |
|WTP Alternate Tunnel Failure Indication |
|(report failure
|(Report Failure (AR address(es))) Address(es))) |
|---------------------------------------->|
| |
+-+-+-+-+-+-+-+ |
| Tunnel | |
| Established | |
+-+-+-+-+-+-+-+ |
|WTP Alternate Tunnel Failure Indication |
|(report clearing failure)
|(Report Clearing Failure) |
|---------------------------------------->|
| |

Figure 5: Setup of an 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 determines
whether an alternate tunnel configuration is required. If an
appropriate alternate tunnel type is selected, then the AC provides
the alternate tunnel encapsulation Alternate Tunnel Encapsulations Type message element containing
the tunnel type and a tunnel-specific information element. The tunnel-
specific
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 Alternate Tunnel
Encapsulations Type message element.

Since an 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 carry the alternate
tunnel encapsulation Alternate
Tunnel Encapsulations Type message element containing the AR list
element corresponding to the selected AR as shown in Figure 5.

On detecting a tunnel failure, the WTP SHALL forward data frames to
the AC and discard the frames. In addition, the 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 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, IEEE
802.11 WTP Alternate Tunnel Fail Failure Indication (defined in this specification).
Section 3.3). It MAY be carried in the WTP Event Request message message,
which is defined in [RFC5415].

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, SSIDs and provide this information to the WTP for the
purpose of load balancing or master-slave mode.

The message element has a status Status field that indicates whether the
message denotes is reporting a failure or the clearing of the previously reported
failure.

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

3. Extensions for CAPWAP Protocol Message Elements Extensions

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

Figure 6: Supported Alternate Tunnel Encapsulations

o Type: <IANA-1> 54 for Supported Alternate Tunnel Encapsulations Type

o Length: The length in bytes, bytes; two bytes for each Alternative tunnel
type
Tunnel-Type that is included

o Tunnel-Type: This is identified by the value defined in
Section 3.2. There may be one or more Tunnel-Types Tunnel-Types, as shows is shown
in Figure 6.

3.2. Alternate Tunnel Encapsulations Type

This message element can be sent by the AC. This message element AC, allows the AC to select
the alternate tunnel encapsulation. This
message element encapsulation, and 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) MAC), and Tunnel
Mode is set to 0 (Local Bridging). Besides, the message element can
also be sent by the WTP to communicate the selected AR(s).

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> 55 for Alternate Tunnel Encapsulation Encapsulations Type

o Length: > 4

o Tunnel-Type: The tunnel type Tunnel-Type is specified by a 2 byte 2-byte value. This
specification defines the values from zero (0) 0 to six (6) 6 as given below. The
remaining values are reserved for future use.

* 0: CAPWAP. This refers to a CAPWAP data channel Data Channel described in
[RFC5415] and [RFC5416].

* 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-UDP. This refers to the UDP encapsulation mode for
Proxy Mobile IPv6 (PMIPv6) described in [RFC5844]. This
encapsulation mode is the basic encapsulation mode and does not
include the TLV header specified in section 7.2, Section 7.2 of [RFC5845].

* 5: GRE. This refers to GRE tunnel encapsulation as described
in [RFC2784].

* 6: GTPv1-U. This refers to GTPv1 user plane the GPRS Tunnelling Protocol (GTP)
User Plane mode as described in [TS29281].

o Info Element: This field contains tunnel specific tunnel-specific configuration
parameters to enable the WTP to setup set up the alternate tunnel. This
specification provides details for this elements element for CAPWAP,
PMIPv6, and GRE. This specification reserves the tunnel type
values for the key tunnel types and defines the most common
message elements. It is anticipated that message elements for the
other protocols (like L2TPv3, etc.) L2TPv3) will be defined in other
specifications in the future.

3.3. IEEE 802.11 WTP Alternate Tunnel Failure Indication

The WTP MAY include the Alternate Tunnel Failure Indication message
in a WTP Event Request message to inform the AC about the status of
the Alternate Tunnel. alternate tunnel. For the case where the WTP establishes data
tunnels with multiple ARs (e.g., under a 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> 1062 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) 1 and 16.

o Status: An 8-bit boolean indicating whether the radio failure is
being reported or cleared. A value of zero 0 is used to clear the
event, while a value of one 1 is used to report the event.

o Reserved: MUST be set to a value of 0 and MUST be ignored by the
receiver.

o Access Router Information Element: The IPv4 address or IPv6 address of the
Access Router that terminates the alternate tunnel. The Access
Router Information Elements allow the WTP to notify the AC of
which AR(s) are unavailable.

4. Alternate Tunnel Types

4.1. CAPWAP based 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: The IPv4 address or IPv6 address 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 is determined by the associated AC policy
policy. (This is consistent with the WTP behavior described in [RFC5415]).
[RFC5415].)
o IEEE 802.11 Tagging Mode Policy: It is used to specify how the
CAPWAP data channel packet Data Channel packets 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. Data Channels. When run over IPv6, the CAPWAP data
channel Data
Channel may use either UDP or UDP-lite. 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

4.2. PMIPv6 based PMIPv6-Based Alternate Tunnel

Proxy Mobile IPv6 (PMIPv6)

A user plane based on PMIPv6 (defined in [RFC5213]) based user plane can also be used
as an 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 UDP encapsulation is
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 (acting as LMA) Information: IPv4 or IPv6 address
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 Information Element .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 10: Alternate Tunnel Encapsulation - PMIPv6

4.3. GRE based GRE-Based Alternate Tunnel

A user plane based on Generic Routing Encapsulation (defined in
[RFC2784]) mode based user
plane can also be used as an alternate tunnel encapsulation
between the WTP and the AR. In this scenario, a WTP and the access router Access
Router represent the two end points endpoints of the GRE tunnel. If GRE encapsulation is
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 Information: The IPv4 or IPv6 address for the
alternate tunnel endpoint.

o GRE Key Information: The Key field is intended to be used for
identifying an individual traffic flow within a tunnel [RFC2890].

The message element structure for GRE encapsulation is shown in Figure 11:

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=5 | Info Element Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. Access Router Information Element .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. GRE Key Element .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 11: Alternate Tunnel Encapsulation - GRE

5. Alternate Tunnel Information Elements

This section defines the various elements described in Section Sections 4.1,
Section
4.2, and Section 4.3.

These information elements can only be included in the Alternate
Tunnel Encapsulations Type message element, element and the IEEE 802.11 WTP
Alternate Tunnel Failure Indication message element as their sub-
elements.

5.1. 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 an IPv4 address, or IPv6 address.This address. For any Tunnel-Type,
this information element SHOULD be contained whatever included in the tunnel type is. Alternate Tunnel
Encapsulations Type message element.

If the Alternate Tunnel Encapsulations Type message element is sent
by the WTP to communicate the selected AR(s), this Access Router
Information Element SHOULD be contained. included in it.

The following are the Access Router Information Elements defined in
this specification. The AC can use one of them to notify the WTP
about the destination information of the data tunnel to the WTP. tunnel. The Elements
containing the AR IPv4 address MUST NOT be used if an IPv6 data
channel with Data
Channel with IPv6 transport is used.

5.1.1. AR IPv4 List Element

This Element element (see Figure 12) 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.

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 12: AR IPv4 List Element

Type: 0

Length: This refers to the total length in octets of the element element,
excluding the Type and Length fields.

AR IPv4 Address: The IPv4 address of the AR. At least one IPv4
address SHALL be present. Multiple addresses may be provided for
load balancing or redundancy.

5.1.2. AR IPv6 List Element

This Element element (see Figure 13) 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 13: AR IPv6 List Element

Type: 1

Length: This refers to the total length in octets of the element
excluding the Type and Length fields.

AR IPv6 Address: The IPv6 address of the AR. At least one IPv6
address SHALL be present. Multiple addresses may be provided for
load balancing or redundancy.

5.2. Tunnel DTLS Policy Element

The AC distributes its DTLS Datagram Transport Layer Security (DTLS) usage
policy for the CAPWAP data tunnel between a WTP and the AR. There
are multiple supported options, which are represented by the bit field
fields 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 obeys the definition in [RFC5415].
If, for reliability reasons, the AC has provided more than one AR
address in the Access Router Information Element, the same Tunnel
DTLS Policy (the last one in Figure 14) is generally applied for all
tunnels associated with those ARs. Otherwise, Tunnel DTLS Policy
MUST be bonded together with each of the Access Router Information
Elements, and the 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 Policy Element Type| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |D|C|R|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. AR Information .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |D|C|R|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. AR Information .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. ...... .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |D|C|R|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 14: Tunnel DTLS Policy Element

Type: 2

Length: This refers to the total length in octets of the element
excluding the Type and Length fields.

Reserved: A set of reserved bits for future use. All implementations
complying with this protocol MUST set to zero 0 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.

D: DTLS-Enabled Data Channel Supported (see [RFC5415]).

C: Clear Text Data Channel Supported (see [RFC5415]).

R: A reserved bit for future use (see [RFC5415]).

AR Information: This means Access Router Information Element. In
this context, each address in AR information Information MUST be one of
previously specified AR addresses.

The

In Figure 14, the last element having that has no AR Information in Figure 14 is the
default tunnel DTLS policy, and which provides options for any address
not previously mentioned. Therefore, the AR information Information field here
is optional. If In this element, if all ARs share the same tunnel DTLS
policy, in this
element, there will not won't be an AR information Information field and or its specific tunnel
DTLS policy.

5.3. IEEE 802.11 Tagging Mode Policy Element

In IEEE 802.11 networks, the IEEE 802.11 Tagging Mode Policy Element
is used to specify how the WTP applies 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 by the IEEE 802.11 WTP
Quality of Service defined in Section 6.22 of [RFC5416].

If, for reliability reasons, the AC has provided more than one AR
address in the Access Router Information Element, the same IEEE
802.11 Tagging Mode Policy (the last one in Figure 15) is generally
applied for all tunnels associated with those ARs. Otherwise, IEEE
802.11 Tagging Mode Policy MUST be bonded together with each of the
Access Router Information Elements, and the WTP will enforce the
independent IEEE 802.11 Tagging Mode 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tagging Mode Policy Ele. Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |P|Q|D|O|I|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. AR Information .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |P|Q|D|O|I|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. AR Information .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. ...... .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |P|Q|D|O|I|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 15: IEEE 802.11 Tagging Mode Policy Element

Type: 3

Length: This refers to the total length in octets of the element
excluding the Type and Length fields.

Reserved: A set of reserved bits for future use.

P: When set, the WTP is to employ the IEEE 802.1p QoS mechanism (see
[RFC5416]).

Q: When the 'P' bit is set, the 'Q' bit is used by the AC to
communicate to the WTP how IEEE 802.1p QoS is to be enforced (see
[RFC5416]).

D: When set, the WTP is to employ the DSCP QoS mechanism (see
[RFC5416]).

O: When the 'D' bit is set, the 'O' bit is used by the AC to
communicate to the WTP how DSCP Differentiated Services Code Point (DSCP)
QoS is to be enforced on the outer (tunneled) header (see [RFC5416]).

I: When the 'D' bit is set, the 'I' bit is used by the AC to
communicate to the WTP how DSCP QoS is to be enforced on the
station's packet (inner) header (see [RFC5416]).

AR Information: This means Access Router Information Element. In
this context, each address in AR information MUST be one of the
previously specified AR addresses.

The

In Figure 15, the last element having that has no AR Information in Figure 15 information is the
default IEEE 802.11 Tagging Mode Policy, and which provides options for
any address not previously mentioned. Therefore, the AR information Information
field here is optional. If all ARs share the same IEEE 802.11
Tagging Mode Policy, in this element, there will not be an AR information
Information field and its specific IEEE 802.11 Tagging Mode Policy.

5.4. 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. Data
Channels. When run over IPv6, the CAPWAP data channel Data Channel may use either
UDP or UDP-lite. UDP-Lite. The AC specifies and configures the WTP for which
the transport protocol is to be used for the CAPWAP data tunnel.

The CAPWAP Transport Protocol Element abides by the definition in
Section 4.6.14 of [RFC5415].

If, for reliability reasons, the AC has provided more than one AR
address in the Access Router Information Element, the same CAPWAP
Transport Protocol (the last one in Figure 16) is generally applied
for all tunnels associated with those ARs. Otherwise, CAPWAP
Transport Protocol MUST be bonded together with each of the Access
Router Information Elements, and the WTP will enforce the independent
CAPWAP Transport Protocol 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Transport | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. AR Information .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Transport | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. AR Information .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. ...... .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Transport | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 16: CAPWAP Transport Protocol Element

Type: 4

Length: 1

Transport: The transport to use for the CAPWAP Data channel. Channel. The
following enumerated values are supported:

1 - UDP-Lite: The UDP-Lite transport protocol is to be used for
the CAPWAP Data channel. Channel. Note that this option MUST NOT be used
if the CAPWAP Control channel Channel is being used over IPv4 and if the
AR address is IPv4 contained in the AR Information Element. Element is an IPv4
address.

2 - UDP: The UDP transport protocol is to be used for the CAPWAP
Data
channel. Channel.

AR Information: This means Access Router Information Element. In
this context, each address in AR information MUST be one of the
previously specified AR addresses.

The

In Figure 16, the last element having that has no AR Information in Figure 16 information is the
default CAPWAP Transport Protocol, and which provides options for any
address not previously mentioned. Therefore, the AR information Information
field here is optional. If all ARs share the same CAPWAP Transport
Protocol, in this element, there will not be an AR information Information field
and its specific CAPWAP Transport Protocol.

5.5. GRE Key Element

If a WTP receives the GRE Key Element in the Alternate Tunnel
Encapsulation
Encapsulations Type message element for GRE selection, the WTP MUST
insert the GRE Key to the encapsulation packet (see [RFC2890]). An
AR acting as a decapsulating tunnel endpoint identifies packets
belonging to a traffic flow based on the Key value.

The GRE Key Element field contains a four octet 4-octet number defined in
[RFC2890].

If, for reliability reasons, the AC has provided more than one AR
address in the Access Router Information Element, a GRE Key Element
MAY be bonded together with each of the Access Router Information
Elements, and the WTP will enforce the independent GRE Key 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GRE Key Element Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GRE Key |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. AR Information .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GRE Key |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. AR Information .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. ...... .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 17: GRE Key Element

Type: 5

Length: This refers to the total length in octets of the element
excluding the Type and Length fields.

GRE Key: The Key field contains a four octet 4-octet number which that is inserted by
the WTP according to [RFC2890].

AR Information: This means Access Router Information Element. In
this context, it SHOULD be restricted to a single address, address and MUST be
the address of one of previously specified AR addresses.

Any address not explicitly mentioned here does not have a GRE key.

5.6. IPv6 MTU Element

If AC has chosen a tunneling mechanism based on IPv6, it SHOULD
support the minimum IPv6 MTU requirements [RFC8200]. This issue is
described in [I-D.ietf-intarea-tunnels]. [ARCH-TUNNELS]. AC SHOULD inform the WTP about the IPv6
MTU information in the "Tunnel Tunnel Info Element" Element field.

If, for reliability reasons, the AC has provided more than one AR
address in the Access Router Information Element, an IPv6 MTU Element
MAY be bonded together with each of the Access Router Information
Elements, and the WTP will enforce the independent IPv6 MTU 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 MTU Element Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Minimum IPv6 MTU | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. AR Information .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Minimum IPv6 MTU | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. AR Information .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ...... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 18: IPv6 MTU Element

Type: 6

Length: This refers to the total length in octets of the element
excluding the Type and Length fields.

Minimum IPv6 MTU: The field contains a two octet 2-octet number indicate indicating the
minimum IPv6 MTU in the tunnel.

AR Information: This means Access Router Information Element. In
this context, each address in AR information MUST be one of
previously specified AR addresses.

6. IANA Considerations

This document requires the following

Per this document, 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 has registered the following values in the
existing CAPWAP "CAPWAP Message Element Type 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 54: Supported Alternate Tunnel Encapsulations Type message element as defined in
Section 3.2. This element
needs to be registered in the existing CAPWAP Message Element 3.1.

o 55: Alternate Tunnel Encapsulations Type
registry, as defined in [RFC5415]. The Type value for this element
needs to be between 1 and 1023.
Section 3.2.

o <IANA-3>. This specification defines the 1062: IEEE 802.11 WTP Alternate Tunnel Failure Indication message element as
defined 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

Per this element needs to be between 1024 and 2047.
o Alternate Tunnel-Types Registry: document, IANA has created a registry called "Alternate
Tunnel-Types" under "CAPWAP Parameters". 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) values 0 through six (6) 6 and
can be found in Section 3.2. Future allocations of values in this name space
namespace are to be assigned by IANA using the "Specification
Required" policy. IANA needs to
create a registry called CAPWAP Alternate Tunnel-Types. policy [RFC8126]. The registry format is given below.

Tunnel-Type Type

Description Value Reference
CAPWAP 0 [RFC5415],[RFC5416] [RFC5415] [RFC5416]
L2TP 1 [RFC2661]
L2TPv3 2 [RFC3931]
IP-IP 3 [RFC2003]
PMIPv6-UDP 4 [RFC5844]
GRE 5 [RFC2784]
GTPv1-U 6 [3GPP TS 29.281]

o Alternate

Per this document, IANA has created a registry called "Alternate
Tunnel Sub-elements Registry: Sub-elements" under "CAPWAP Parameters". This specification
defines the Alternate Tunnel Sub-elements. Currently, these
information elements can only be included in the Alternate Tunnel
Encapsulations Type message element, and element with the IEEE 802.11 WTP
Alternate Tunnel Failure Indication message element as their its sub-
elements. These information elements contains contain a Type field. The
namespace for the field is 16 bits (0-65535). This specification
defines values, zero (0) values 0 through six (6) 6 in Section 5. This namespace is managed
by IANA IANA, and assignments require an Expert
Review.

Type Type Review [RFC8126].

Description Value
AR IPv4 List 0
AR IPv6 List 1
Tunnel DTLS Policy 2
IEEE 802.11 Tagging Mode Policy 3
CAPWAP Transport Protocol 4
GRE Key 5
IPv6 MTU 6

7. 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 to the control plane compared to
[RFC5415] and [RFC5416]. In the data plane, if the encapsulation
type selected itself is not secured, it is suggested to protect the
tunnel by using known secure methods, such as IPSec. IPsec.

8. Contributors

The authors would like to thank Andreas Schultz, Hong Liu, Yifan
Chen, Chunju Shao, Li Xue, Jianjie You, Jin Li, Joe Touch, Alexey
Melnikov, Kathleen Moriarty, Mirja Kuehlewind, Catherine Meadows, and
Paul Kyzivat for their valuable comments.

9. References

9.1.

8.1. Normative References

[RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003,
DOI 10.17487/RFC2003, October 1996,
<https://www.rfc-editor.org/info/rfc2003>.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.

[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,
<https://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,
<https://www.rfc-editor.org/info/rfc2784>.

[RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE",
RFC 2890, DOI 10.17487/RFC2890, September 2000,
<https://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, <https://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,
<https://www.rfc-editor.org/info/rfc3931>.

[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,
<https://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,
<https://www.rfc-editor.org/info/rfc5416>.

[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.

[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.

[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.

9.2.

8.2. Informative References

[I-D.ietf-intarea-tunnels]

[ARCH-TUNNELS]
Touch, J. and M. Townsley, "IP Tunnels in the Internet
Architecture", draft-ietf-intarea-tunnels-08 (work Work in
progress), Progress, draft-ietf-intarea-
tunnels-08, January 2018.

[RFC5213] Gundavelli, S., Ed., Leung, K., Devarapalli, V.,
Chowdhury, K., and B. Patil, "Proxy Mobile IPv6",
RFC 5213, DOI 10.17487/RFC5213, August 2008,
<https://www.rfc-editor.org/info/rfc5213>.

[RFC5844] Wakikawa, R. and S. Gundavelli, "IPv4 Support for Proxy
Mobile IPv6", RFC 5844, DOI 10.17487/RFC5844, May 2010,
<https://www.rfc-editor.org/info/rfc5844>.

[RFC5845] Muhanna, A., Khalil, M., Gundavelli, S., and K. Leung,
"Generic Routing Encapsulation (GRE) Key Option for Proxy
Mobile IPv6", RFC 5845, DOI 10.17487/RFC5845, June 2010,
<https://www.rfc-editor.org/info/rfc5845>.

[RFC7494] Shao, C., Deng, H., Pazhyannur, R., Bari, F., Zhang, R.,
and S. Matsushima, "IEEE 802.11 Medium Access Control
(MAC) Profile for Control and Provisioning of Wireless
Access Points (CAPWAP)", RFC 7494, DOI 10.17487/RFC7494,
April 2015, <https://www.rfc-editor.org/info/rfc7494>.

[TS29281] "3rd Generation Partnership Project; Technical
Specification Group Core Network and Terminals; General 3GPP, "General Packet Radio System (GPRS) Tunnelling
Protocol User Plane (GTPv1-U)", 3GPP TS 29.281, V13.1.0,
March 2016.

Contributors

Authors' Addresses

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

Email: zhangr@gsta.com

Rajesh S. Pazhyannur
Cisco
170 West Tasman Drive
San Jose, CA 95134
USA
United States of America

Email: rpazhyan@cisco.com

Sri Gundavelli
Cisco
170 West Tasman Drive
San Jose, CA 95134
USA
United States of America

Email: sgundave@cisco.com
Zhen Cao
Huawei
Xinxi Rd. 3
Beijing 100085
China

Email: zhencao.ietf@gmail.com

Hui Deng
Huawei
Xinxi Rd. 3
Beijing 100085
China

Email: denghui02@gmail.com

Zongpeng Du
Huawei
No.156 Beiqing Rd. Z-park, HaiDian District
Beijing 100095
China

Email: duzongpeng@huawei.com