| Opsawg Working Group | R. Zhang |
| Internet-Draft | China Telecom |
| Intended status: Experimental | R. Pazhyannur |
| Expires: March 12, 2018 | S. Gundavelli |
| Cisco | |
| Z. Cao | |
| H. Deng | |
| Z. Du | |
| Huawei | |
| September 8, 2017 |
Alternate Tunnel Encapsulation for Data Frames in CAPWAP
draft-ietf-opsawg-capwap-alt-tunnel-10
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. Furthermore, it may also be desirable to use different tunnel encapsulation modes between the WTP and the Access Router. This document defines extension to CAPWAP protocol for supporting 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 such as IP-IP, IP-GRE, CAPWAP. The WTP may advertise support for alternate tunnel encapsulation during the discovery and join process and AC may select one of the supported alternate tunnel encapsulation types while configuring the WTP.
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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 https://datatracker.ietf.org/drafts/current/.
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This Internet-Draft will expire on March 12, 2018.
Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved.
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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:
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.
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).
+-----+
| WTP |
+-----+
\\
\\ CAPWAP Control Channel +----------+
++=========================| AC |
// CAPWAP Data Channel: | |
// IEEE 802.11 Mgmt traffic | |
// Data Frames +----------+
//
+-----+
| WTP |
+-----+
Figure 2: Centralized Control and Centralized Data
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 AC 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. 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]).
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
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.
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. 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 can notify multiple AR addresses for load balancing or redundancy.
+----+
| 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-DATA (SSID1) +---------------+
| +---------------------------|Access Router 2|
| +---------------+
|
| VNO 2
| CAPWAP-DATA (SSID2) +---------------+
+-----------------------------|Access Router 3|
+---------------+
Figure 4: Third-party WLAN Service Provider
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].
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 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).
This document was started to accommodate Service Provider's need of a more flexible deployment mode with alternative tunnels [RFC7494]. Experiments and tests have been done for this alt-tunnel network infrastructure. However important, the deployment of relevant technology is yet to complete. This experimental document is intended to serve as a historical reference for any future work as to the operational and deployment requirements..
+-+-+-+-+-+-+ +-+-+-+-+-+-+
| 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
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.
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.
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). It MAY be carried in the CAPWAP Station Configuration Request 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, 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.
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-Type1 | Tunnel-Type [2...N] +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Supported Alternate Tunnel Encapsulations
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
The Alternate Tunnel Failure Indication message element is sent by the WTP to inform the AC about the status of the Alternate Tunnel. It MAY be included in the CAPWAP Station Configuration Request message. 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
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:
The message element structure for CAPWAP encapsulation is shown in
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
Proxy Mobile IPv6 (PMIPv6) (defined in [RFC5213]) based user plane can also be used as 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:
The message element structure for PMIPv6 encapsulation is shown in
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
Generic Routing Encapsulation (defined in [RFC2784]) mode based user plane can also be used as alternate tunnel encapsulation between the WTP and the AR. In this scenario, a WTP and the access routers represent the two end points 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:
The message element structure for GRE encapsulation is shown in
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
This section defines the various elements described in Section 4.1, Section 4.2, and Section 4.3.
These information elements can only be inluded in the Alternate Tunnel Encapsulations Type message element, and the IEEE 802.11 WTP Alternate Tunnel Failure Indication message element as their sub-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, or IPv6 address.This information element SHOULD be contained whatever the tunnel type is.
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 with IPv6 transport is used.
This 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 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.
This 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: IPv6 address of the AR. At least one IPv6 address SHALL be present. Multiple addresses may be provided for load balancing or redundancy.
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 obeys 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 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 Policy Element Type| Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved |A|D|C|R| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . AR Information (optional) . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 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 (see [RFC5415]).
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].
If there are more than one ARs information provided by the AC for reliability reasons, the same IEEE 802.11 Tagging Mode Policy (see Figure 15) is generally applied for all tunnels associated with the ARs. Otherwise, IEEE 802.11 Tagging Mode Policy MUST be bonding together with each of the ARs, then WTP will enforce the independent tunnel 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 |A|P|Q|D|O|I| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . AR Information (optional) . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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.
A: If A bit is set, there is an AR information associated with the Tagging Mode policy. There may be an array of pairs binding Tagging Mode policy information and AR information contained in the Tagging Mode Policy Element. Otherwise, the same Tagging Mode Policy (see Figure 15) is generally applied for all tunnels associated with the ARs configured by the AC.
P: When set, the WTP is to employ the 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 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 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]).
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=4 | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Transport | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 16: CAPWAP Transport Protocol Element
Type: 4
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.
If a WTP receives the GRE Key Element in the Alternate Tunnel Encapsulation message element for GRE 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].
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 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 number which is inserted by the WTP according to [RFC2890].
If AC has chosen a tunneling mechanism based on IPv6, it SHOULD support the minimum IPv6 MTU requirements [RFC2460]. This issue is described in [I-D.ietf-intarea-tunnels]. AC SHOULD inform the WTP about the IPv6 MTU information in the "Tunnel Info Element" field.
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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 number indicate the minimum IPv6 MTU in the tunnel.
Tunnel-Type Type Value Reference
CAPWAP 0 [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]
Type Type 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
This document requires the following IANA 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.
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 Kühlewind, Catherine Meadows, and Paul Kyzivat for their valuable comments.
| [I-D.ietf-intarea-tunnels] | Touch, J. and M. Townsley, "IP Tunnels in the Internet Architecture", Internet-Draft draft-ietf-intarea-tunnels-07, June 2017. |
| [RFC5213] | Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K. and B. Patil, "Proxy Mobile IPv6", RFC 5213, DOI 10.17487/RFC5213, August 2008. |
| [RFC5844] | Wakikawa, R. and S. Gundavelli, "IPv4 Support for Proxy Mobile IPv6", RFC 5844, DOI 10.17487/RFC5844, May 2010. |
| [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. |
| [TS29281] | "3rd Generation Partnership Project; Technical Specification Group Core Network and Terminals; General Packet Radio System (GPRS) Tunnelling Protocol User Plane (GTPv1-U)", 2016. |