Opsawg Working Group R. Zhang Internet-Draft China Telecom Intended status: Standards Track Z. Cao Expires: January 9, 2017 H. Deng China Mobile R. Pazhyannur S. Gundavelli Cisco L. Xue J. You Huawei July 8, 2016 Alternate Tunnel Encapsulation for Data Frames in CAPWAP draft-ietf-opsawg-capwap-alt-tunnel-08 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. 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 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/. Zhang, et al. Expires January 9, 2017 [Page 1] Internet-Draft Alternate-- Tunnel July 2016 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 January 9, 2017. Copyright Notice Copyright (c) 2016 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Zhang, et al. Expires January 9, 2017 [Page 2] Internet-Draft Alternate-- Tunnel July 2016 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Conventions used in this document . . . . . . . . . . . . 8 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 8 2. Alternate Tunnel Encapsulation . . . . . . . . . . . . . . . . 9 2.1. Description . . . . . . . . . . . . . . . . . . . . . . . 10 3. Protocol Considerations . . . . . . . . . . . . . . . . . . . 11 3.1. Supported Alternate Tunnel Encapsulations . . . . . . . . 11 3.2. Alternate Tunnel Encapsulations Type . . . . . . . . . . . 12 3.3. IEEE 802.11 WTP Alternate Tunnel Failure Indication . . . 13 3.4. CAPWAP based Alternate Tunnel . . . . . . . . . . . . . . 14 3.5. PMIPv6 based Alternate Tunnel . . . . . . . . . . . . . . 15 3.6. GRE based Alternate Tunnel . . . . . . . . . . . . . . . . 16 3.7. Alternate Tunnel Information Elements . . . . . . . . . . 16 3.7.1. Access Router Information Elements . . . . . . . . . . 16 3.7.2. IEEE 802.11 WLAN Configuration Response . . . . . . . 17 3.7.3. Tunnel DTLS Policy Element . . . . . . . . . . . . . . 17 3.7.4. IEEE 802.11 Tagging Mode Policy Element . . . . . . . 18 3.7.5. CAPWAP Transport Protocol Element . . . . . . . . . . 19 3.7.6. GRE Key Element . . . . . . . . . . . . . . . . . . . 19 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 5. Security Considerations . . . . . . . . . . . . . . . . . . . 21 6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 21 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21 7.1. Normative References . . . . . . . . . . . . . . . . . . . 21 7.2. Informative References . . . . . . . . . . . . . . . . . . 22 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23 Zhang, et al. Expires January 9, 2017 [Page 3] Internet-Draft Alternate-- Tunnel July 2016 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. Zhang, et al. Expires January 9, 2017 [Page 4] Internet-Draft Alternate-- Tunnel July 2016 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. Zhang, et al. Expires January 9, 2017 [Page 5] Internet-Draft Alternate-- Tunnel July 2016 +-----+ | 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 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) Zhang, et al. Expires January 9, 2017 [Page 6] Internet-Draft Alternate-- Tunnel July 2016 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. 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. Zhang, et al. Expires January 9, 2017 [Page 7] Internet-Draft Alternate-- Tunnel July 2016 +----+ | 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 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 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. Zhang, et al. Expires January 9, 2017 [Page 8] Internet-Draft Alternate-- Tunnel July 2016 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 Zhang, et al. Expires January 9, 2017 [Page 9] Internet-Draft Alternate-- Tunnel July 2016 2.1. Description +-+-+-+-+-+-+ +-+-+-+-+-+-+ | 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) | |---------------------------------------->| | | Zhang, et al. Expires January 9, 2017 [Page 10] Internet-Draft Alternate-- Tunnel July 2016 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. 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: Zhang, et al. Expires January 9, 2017 [Page 11] Internet-Draft Alternate-- Tunnel July 2016 0 1 2 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- | Tunnel-Type 1 | Tunnel-Type [2..N] +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- Figure 6: Supported Alternate Tunnel Encapsulations o Type: for Supported Alternate Tunnel Encapsulations o Length: The length in bytes, one byte for each Alternative tunnel type that is included. 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: 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]. Zhang, et al. Expires January 9, 2017 [Page 12] Internet-Draft Alternate-- Tunnel July 2016 * 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 tunneling encapsulation described in [RFC5844]. * 5: GRE. This refers to GRE tunnel encapsulation as described in [RFC2784]. * 6: GTPv1-U. This refers to GTPv1 user plane mode as described in [TS29281]. 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. This specification reserves the tunnel type values for the key tunnel types and defines the most common message elements. 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 Zhang, et al. Expires January 9, 2017 [Page 13] Internet-Draft Alternate-- Tunnel July 2016 o Type: 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 Reserved: Must be set to a value of 0 and must be ignored by the receiver. o Access Router Information Element: 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. 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 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: Zhang, et al. Expires January 9, 2017 [Page 14] Internet-Draft Alternate-- Tunnel July 2016 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]) 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: o Access Router (acts 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 (LMA) Information Element . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 10: Alternate Tunnel Encapsulation - PMIPv6 Zhang, et al. Expires January 9, 2017 [Page 15] Internet-Draft Alternate-- Tunnel July 2016 3.6. GRE based Alternate Tunnel Generic Routing Encapsulation mode [RFC2784] 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. The information elements needed for supporting this mode are defined in Section 3.7 and Section 3.7.6. 3.7. Alternate Tunnel Information Elements This section defines the various elements described in Section 3.4 and Section 3.5 3.7.1. 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 with IPv6 transport is used. 3.7.1.1. 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. 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 Zhang, et al. Expires January 9, 2017 [Page 16] Internet-Draft Alternate-- Tunnel July 2016 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. 3.7.1.2. 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. 3.7.2. 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. 3.7.3. 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 Zhang, et al. Expires January 9, 2017 [Page 17] Internet-Draft Alternate-- Tunnel July 2016 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 13) 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 Element Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved |A|D|C|R| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . AR Information (optional) . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 13: 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 13) 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]). 3.7.4. 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]). Zhang, et al. Expires January 9, 2017 [Page 18] Internet-Draft Alternate-- Tunnel July 2016 The IEEE 802.11 Tagging Mode Policy abides the IEEE 802.11 WTP Quality of Service defined in Section 6.22 of [RFC5416]. 3.7.5. 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 14: 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. 3.7.6. GRE Key Element 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 Zhang, et al. Expires January 9, 2017 [Page 19] Internet-Draft Alternate-- Tunnel July 2016 [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 15: 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 . 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 . 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 . 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 Alternate Tunnel-Types Registry: 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 Zhang, et al. Expires January 9, 2017 [Page 20] Internet-Draft Alternate-- Tunnel July 2016 registry format is given below. o 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] 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 The authors would like to thank Andreas Schultz, Hong Liu, Yifan Chen, Chunju Shao, 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, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ RFC2119, March 1997, . [RFC2661] Townsley, W., Valencia, A., Rubens, A., Pall, G., Zorn, Zhang, et al. Expires January 9, 2017 [Page 21] Internet-Draft Alternate-- Tunnel July 2016 G., and B. Palter, "Layer Two Tunneling Protocol "L2TP"", RFC 2661, DOI 10.17487/RFC2661, August 1999, . [RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, DOI 10.17487/RFC2784, March 2000, . [RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE", RFC 2890, DOI 10.17487/RFC2890, September 2000, . [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, . [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, . [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, . 7.2. Informative References [RFC5213] Gundavelli, S., Ed., 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, . [TS29281] "3rd Generation Partnership Project; Technical Specification Group Core Network and Terminals; General Packet Radio System (GPRS) Tunnelling Protocol User Plane (GTPv1-U)", 2016. Zhang, et al. Expires January 9, 2017 [Page 22] Internet-Draft Alternate-- Tunnel July 2016 Authors' Addresses Rong Zhang China Telecom No.109 Zhongshandadao avenue Guangzhou, 510630 China Phone: Fax: Email: zhangr@gsta.com URI: 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 Phone: Fax: Email: rpazhyan@cisco.com URI: Zhang, et al. Expires January 9, 2017 [Page 23] Internet-Draft Alternate-- Tunnel July 2016 Sri Gundavelli Cisco 170 West Tasman Drive San Jose, CA 95134, USA Phone: Fax: Email: sgundave@cisco.com URI: Li Xue Huawei No.156 Beiqing Rd. Z-park, HaiDian District Beijing, China Phone: Fax: Email: xueli@huawei.com URI: Jianjie You Huawei 101 Software Avenue, Yuhuatai District Nanjing, 210012 China Email: youjianjie@huawei.com Zhang, et al. Expires January 9, 2017 [Page 24]