RFC 8350
Alternate Tunnel Encapsulation for Data Frames in Control and Provisioning of Wireless Access Points (CAPWAP)
RFC 8350: Alternate Tunnel Encapsulation for Data Frames in CAPWAP ✨
Bestie, the title block is giving: this is RFC 8350 💖, written by R. Zhang (China Telecom), R. Pazhyannur and S. Gundavelli (Cisco), and Z. Cao, H. Deng, and Z. Du (Huawei). It's dated April 2018 📅 and the category is Experimental 🧪. The ISSN is 2070-1721. There's no Obsoletes or Updates line in the header, so it doesn't replace or change any other RFC 🦋.
Abstract 🌸
Okay so CAPWAP (Control and Provisioning of Wireless Access Points) is the protocol for wrapping up a station's data frames as they travel between the Wireless Transmission Point (WTP) and the Access Controller (AC) 🎀. The station's IEEE 802.11 data frames can either be locally bridged or tunneled to the AC, and when they're tunneled, a CAPWAP Data Channel does the tunneling 🫶.
Here's the tea: in lots of deployments, you want those frames sent to something other than the AC, like an Access Router (AR) 👑. You might also want different tunnel encapsulation modes between the WTP and the Access Router 🧚. This document adds an extension to CAPWAP for exactly that, and it calls it alternate tunnel encapsulation 💅.
Alternate tunnel encapsulation lets 1) the WTP tunnel non-management data frames to an endpoint that isn't the AC, and 2) the WTP tunnel using one of many known encapsulation types, like IP-IP, IP-GRE, or CAPWAP 🌈. The WTP can advertise that it supports alternate tunnel encapsulation during discovery and join, and then the AC can pick one of the supported types while it configures the WTP ✨. Iconic, honestly.
Status of This Memo 💜
Heads up: this document is not an Internet Standards Track specification 🙈. It's published for examination, experimental implementation, and evaluation 🔬.
It defines an Experimental Protocol for the Internet community 🧪. It's a product of the Internet Engineering Task Force (IETF) and represents the consensus of the IETF community. It got public review and was approved for publication by the Internet Engineering Steering Group (IESG) 💖. Not every document the IESG approves is a candidate for any level of Internet Standard, so check Section 2 of RFC 7841 for the details 📖.
For the current status, any errata, and how to send feedback, go to https://www.rfc-editor.org/info/rfc8350 🦋.
Copyright Notice 🎀
Copyright (c) 2018 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 (https://trustee.ietf.org/license-info) as they were in effect on the date of publication. Please read these carefully, because they describe your rights and restrictions for 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 they're provided without warranty as described in the Simplified BSD License 🌸.
Table of Contents 📚
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions Used in This Document . . . . . . . . . . . . 7
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 7
1.3. History of the Document . . . . . . . . . . . . . . . . . 8
2. Alternate Tunnel Encapsulation Overview . . . . . . . . . . . 9
3. Extensions for CAPWAP Protocol Message Elements . . . . . . . 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 Alternate Tunnel . . . . . . . . . . . . . . 13
4.2. PMIPv6-Based Alternate Tunnel . . . . . . . . . . . . . . 14
4.3. GRE-Based Alternate Tunnel . . . . . . . . . . . . . . . 15
5. Alternate Tunnel Information Elements . . . . . . . . . . . . 16
5.1. Access Router Information Elements . . . . . . . . . . . 16
5.1.1. AR IPv4 List Element . . . . . . . . . . . . . . . . 16
5.1.2. AR IPv6 List Element . . . . . . . . . . . . . . . . 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 . . . . . . . . . . . . . . . . . . . . . 24
7. Security Considerations . . . . . . . . . . . . . . . . . . . 25
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 25
8.1. Normative References . . . . . . . . . . . . . . . . . . 25
8.2. Informative References . . . . . . . . . . . . . . . . . 27
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 281. Introduction ✨
Okay bestie, so Service Providers are deploying huge Wi-Fi networks with hundreds of thousands of Access Points (APs). In CAPWAP land these are called Wireless Transmission Points (WTPs) [RFC5415] 📶. These networks carry traffic from mobile users, and that traffic is already massive and still growing fast 📈. So operators are hunting for scalable solutions. The scalability requirement can be met by splitting the control/management plane from the data plane, so the data plane can scale on its own 💅. This specification gives a way to make that separation happen 🦋.
CAPWAP [RFC5415] [RFC5416] defines a tunnel mode that describes how the WTP handles the data plane (user traffic). There are three types:
- Local Bridging: All data frames are locally bridged.
- IEEE 802.3 Tunnel: All data frames are tunneled to the Access Controller (AC) in IEEE 802.3 format.
- 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 sits in a centralized location, and the WTPs locally bridge the data plane. That gives you a centralized control plane with a distributed data plane. It has two benefits: 1) it reduces the scale requirement on the data traffic handling capability of the AC, and 2) it leads to more efficient/optimal routing of data traffic while maintaining centralized control/management. Iconic, honestly 👑.
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 DataThe AC handles control of WTPs. It also handles the IEEE 802.11 management traffic to and from the stations 🧚. There's a CAPWAP Control and Data Channel between the WTP and the AC. Note that even though no user traffic gets transported between the WTP and AC, there is still a CAPWAP Data Channel 🙈. That 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, using either the IEEE 802.3 Tunnel or 802.11 Tunnel configurations. Operators go with this when they need to tunnel the user traffic 💖. The tunneling requirement may be driven by the need to apply policy at the AC. That requirement could be met in the locally bridged system (Figure 1) if the Access Router (AR) implemented the required policy. But in many deployments, the operator managing the WTP is different from 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. Ngl, the operator drama is real 💀.
+-----+
| WTP |
+-----+
\\
\\ CAPWAP Control Channel +----------+
++=========================| AC |
// CAPWAP Data Channel: | |
// IEEE 802.11 Mgmt Traffic | |
// Data Frames +----------+
//
+-----+
| WTP |
+-----+
Figure 2: Centralized Control and Centralized DataThe big difference from the locally bridged system is that the data frames get tunneled to the AC instead of being locally bridged. Figure 2 has two shortcomings: 1) it does not allow the WTP to tunnel data frames to an endpoint different from the AC, and 2) it does not allow the WTP to tunnel data frames using any encapsulation other than CAPWAP (as specified in Section 4.4.2 of [RFC5415]). Not it, fr fr 🙅♀️.
Figure 3 shows a system where the WTP tunnels data frames to an alternate entity that isn't the AC 🦋. The WTP also uses an alternate tunnel encapsulation such as Layer 2 Tunneling Protocol (L2TP), L2TPv3, IP-in-IP, IP/GRE, etc. This enables 1) independent scaling of the data plane and 2) leveraging of commonly used tunnel encapsulations such as L2TP, GRE, etc. Main character energy ✨.
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-in-IP, CAPWAP, etc.)
Figure 3: Centralized Control with an Alternate Tunnel for DataThe 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, and the AC configures one of the advertised types 📣. As Figure 3 shows, there's a CAPWAP Control and Data Channel between the WTP and AC. The CAPWAP Data Channel carries the stations' management traffic, same as in the locally bridged system. The main reason to keep a CAPWAP Data Channel is to stay similar to the locally bridged system 🫶. So the WTP maintains three tunnels: CAPWAP Control, CAPWAP Data, and another alternate tunnel for the data frames. The data frames get transported by that 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. It 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. Lots of moving parts, but make it make sense 🎀.
The alternate tunnel encapsulation also supports the third-party WLAN service provider scenario (i.e., Virtual Network Operator (VNO)) 🌸. In this scenario, the WLAN provider owns the WTP and AC resources, while the VNOs rent 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 Figure 4 shows, VNO 1 and VNO 2 don't possess the network access resources. They still provide services by acquiring resources from the WLAN provider 💅. A WTP can support up to 16 Service Set Identifiers (SSIDs), so the WLAN provider can provide network access service for different providers with different SSIDs. For example, SSID1 is advertised by the WTP for VNO 1, while SSID2 is advertised by the WTP for VNO 2. That means the data traffic from the user can be directly steered to the corresponding Access Router of the VNO who owns that user 🍓. As Figure 4 shows, the 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 Provider1.1. Conventions Used in 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 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 (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 a Radio Frequency (RF) antenna and wireless Physical layer (PHY) to transmit and receive station traffic for wireless access networks. 📡
CAPWAP Control Channel: A 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 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
This document was started to accommodate Service Providers' need for a more flexible deployment mode with alternative tunnels [RFC7494]. Experiments and tests have been done for this alternate tunnel network infrastructure. However important, the deployment of relevant technology is yet to be completed. This Experimental document is intended to serve as an archival record for any future work on the operational and deployment requirements. 🗂️✨
2. Alternate Tunnel Encapsulation Overview 🦋
okay so let's walk through how a WTP and an AC set up an alternate tunnel, bestie 💅
+-+-+-+-+-+-+ +-+-+-+-+-+-+
| 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 (AR Address(es))) |
|---------------------------------------->|
| |
+-+-+-+-+-+-+-+ |
| Tunnel | |
| Established | |
+-+-+-+-+-+-+-+ |
|WTP Alternate Tunnel Failure Indication |
|(Report Clearing Failure) |
|---------------------------------------->|
| |Figure 5: Setup of an Alternate Tunnel
The example above shows how an alternate tunnel encapsulation may get set up ✨ When the WTP joins the AC, it should indicate its alternate tunnel encapsulation capability 🎀 The AC then decides whether an alternate tunnel configuration is needed. If it picks a suitable alternate tunnel type, the AC sends the Alternate Tunnel Encapsulations Type message element, which holds the tunnel type and a tunnel-specific information element. That tunnel-specific information element could, for example, carry something like the IP address of the tunnel termination point. Then the WTP sets up the alternate tunnel using that Alternate Tunnel Encapsulations Type message element 🦋
Since an AC can set up a WTP with more than one AR for the WTP to use for its data tunnels carrying user traffic, it's helpful for the WTP to tell everyone which AR it picked 💖 To make that happen, the IEEE 802.11 WLAN Configuration Response may carry the Alternate Tunnel Encapsulations Type message element with the AR list element for the selected AR, as shown in Figure 5 🌸
When the WTP detects a tunnel failure, it SHALL forward data frames to the AC and discard the frames 😭 On top of that, the WTP may dissociate existing clients and refuse association requests from new clients. Depending on the implementation and the deployment scenario, the AC may decide to reconfigure the WLAN (on the WTP) to Local Bridging mode, or to tunnel frames to the AC 🧚 When the WTP detects an alternate tunnel failure, it lets the AC know using a message element called IEEE 802.11 WTP Alternate Tunnel Failure Indication (defined in Section 3.3). It MAY be carried in the WTP Event Request message, which is defined in [RFC5415] 💅
The WTP also needs to tell the AC which AR(s) are unavailable 👑 This matters a lot in the VNO scenario, where the AC of the WLAN service provider has to keep track of which AR addresses go with which VNOs and SSIDs, and pass that info to the WTP for load balancing or master-slave mode. Main character energy, honestly 💜
The message element has a Status field that says whether the message is reporting a failure or clearing a failure that was reported before ✨
And if the AC is unreachable but the tunnel endpoint is still reachable, what the WTP does is up to the implementation 🌈 For example, the WTP could choose to either tear down the alternate tunnel or let the existing user's traffic keep getting tunneled 🫶
3. Extensions for CAPWAP Protocol Message Elements 🎀
3.1. Supported Alternate Tunnel Encapsulations 💖
This message element is sent by a WTP to say that it can support alternate tunnel encapsulations 💅 It 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
- Type:
54for Supported Alternate Tunnel Encapsulations Type - Length: The length in bytes; two bytes for each Alternative Tunnel-Type that is included
- Tunnel-Type: This is identified by the value defined in Section 3.2. There may be one or more Tunnel-Types, as is shown in Figure 6.
3.2. Alternate Tunnel Encapsulations Type 🦋
This message element can be sent by the AC 🌸 It lets the AC pick the alternate tunnel encapsulation, and it may come 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 can also be sent by the WTP to tell everyone which AR(s) it selected 🧚 It 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
- Type:
55for Alternate Tunnel Encapsulations Type - Length:
> 4 - Tunnel-Type: The Tunnel-Type is specified by a 2-byte value. This specification defines the values from
0to6as given below. The remaining values are reserved for future use.0: CAPWAP. This refers to a CAPWAP 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 of [RFC5845].5: GRE. This refers to GRE tunnel encapsulation as described in [RFC2784].6: GTPv1-U. This refers to the GPRS Tunnelling Protocol (GTP) User Plane mode as described in [TS.3GPP.29.281].
- Info Element: This field contains tunnel-specific configuration parameters to enable the WTP to set up the alternate tunnel. This specification provides details for this 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) 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 keep the AC posted on the status of the alternate tunnel 💜 When the WTP sets up data tunnels with multiple ARs (for example, in a VNO scenario), it MUST? No, it needs to tell the AC 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
- Type:
1062for IEEE 802.11 WTP Alternate Tunnel Failure Indication - Length:
> 4 - WLAN ID: An 8-bit value specifying the WLAN Identifier. The value MUST be between 1 and 16.
- Status: An 8-bit boolean indicating whether the radio failure is being reported or cleared. A value of
0is used to clear the event, while a value of1is used to report the event. - Reserved: MUST be set to a value of
0and MUST be ignored by the receiver. - Access Router Information Element: The IPv4 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 Alternate Tunnel 🌸
okay so if the AC picks CAPWAP encapsulation and configures it on the WTP, the Info Element field from Section 3.2 SHOULD carry these four things 🫶
- Access Router Information: the IPv4 or IPv6 address of the Access Router for the alternate tunnel 📍
- Tunnel DTLS Policy: CAPWAP lets you optionally protect data packets with DTLS 🔐. Turning on packet protection on a WTP isn't mandatory. The AC policy decides whether it happens. (This matches the WTP behavior in [RFC5415], so it's giving consistency ✨)
- IEEE 802.11 Tagging Mode Policy: this one controls how CAPWAP Data Channel packets get tagged for QoS purposes. See [RFC5416] for the full tea 🎀
- CAPWAP Transport Protocol: CAPWAP supports both UDP and UDP-Lite (see [RFC3828]). Over IPv4, the CAPWAP Data Channels use UDP. Over IPv6, they can use either UDP or UDP-Lite 🦋
the message element structure for CAPWAP encapsulation is 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 - CAPWAP4.2. PMIPv6-Based Alternate Tunnel 🧚
a user plane based on PMIPv6 (defined in [RFC5213]) can also be used as an alternate tunnel encapsulation between the WTP and the AR. in this setup, the WTP acts as the Mobile Access Gateway (MAG) function, managing the mobility-related signaling for a station attached to the WTP IEEE 802.11 radio access. the Local Mobility Anchor (LMA) function lives at the AR 🏠. if PMIPv6 UDP encapsulation is selected by the AC and configured by the AC to a WTP, the Info Element field from Section 3.2 SHOULD contain this:
- Access Router (acting as LMA) Information: the IPv4 or IPv6 address for the alternate tunnel endpoint 💜
the message element structure for PMIPv6 encapsulation is 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 - PMIPv64.3. GRE-Based Alternate Tunnel 🌈
a user plane based on Generic Routing Encapsulation (defined in [RFC2784]) can also be used as an alternate tunnel encapsulation between the WTP and the AR. here the WTP and the Access Router are the two endpoints of the GRE tunnel 🤝. if GRE is selected by the AC and configured by the AC to a WTP, the Info Element field from Section 3.2 SHOULD contain this:
- Access Router Information: the IPv4 or IPv6 address for the alternate tunnel endpoint 📍
- GRE Key Information: the Key field is meant for identifying an individual traffic flow within a tunnel [RFC2890] 🔑
the message element structure for GRE is 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 - GRE5. Alternate Tunnel Information Elements 👑
this section defines the various elements described in Sections 4.1, 4.2, and 4.3 💖
these information elements can only be included in the Alternate Tunnel Encapsulations Type message element and the IEEE 802.11 WTP Alternate Tunnel Failure Indication message element, as their sub-elements. no other place, bestie 🙅♀️
5.1. Access Router Information Elements 🦋
the Access Router Information Elements let the AC tell a WTP which AR(s) are available for setting up a data tunnel. the AR information can be an IPv4 or IPv6 address. for any Tunnel-Type, this information element SHOULD be included in the Alternate Tunnel Encapsulations Type message element 💅
if the WTP sends the Alternate Tunnel Encapsulations Type message element to communicate the selected AR(s), this Access Router Information Element SHOULD be included in it ✨
these are the Access Router Information Elements defined in this specification. the AC can use one of them to tell the WTP about the destination information of the data tunnel. Elements containing the AR IPv4 address MUST NOT be used if an IPv6 Data Channel with IPv6 transport is used. no exceptions, periodt 🚫
5.1.1. AR IPv4 List Element 🌸
this element (see Figure 12) is how the AC configures a WTP with the AR IPv4 address the WTP can use to set up 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: the total length in octets of the element, not counting the Type and Length fields 🧮
- AR IPv4 Address: the IPv4 address of the AR. at least one IPv4 address SHALL be present. you can provide multiple addresses for load balancing or redundancy ⚖️
5.1.2. AR IPv6 List Element 🧚
this element (see Figure 13) is how the AC configures a WTP with the AR IPv6 address the WTP can use to set up 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: the total length in octets of the element, not counting the Type and Length fields 🧮
- AR IPv6 Address: the IPv6 address of the AR. at least one IPv6 address SHALL be present. you can provide multiple addresses for load balancing or redundancy ⚖️
5.2. Tunnel DTLS Policy Element 🔐💖
okay so the AC hands out its DTLS usage policy for the CAPWAP data tunnel between a WTP and the AR 🫶 there are a few options, and they're shown as bit fields (defined in AC Descriptor message elements). the WTP MUST abide by one of the options for tunneling user traffic with AR. this element follows the definition in [RFC5415] ✨
ok now the sneaky bit: if the AC gave you more than one AR address in the Access Router Information Element (for reliability, you know, backup plans 🙄), the same Tunnel DTLS Policy (the last one in Figure 14) is usually applied to every tunnel tied to those ARs. otherwise, Tunnel DTLS Policy MUST be bonded together with each of the Access Router Information Elements, and the WTP will enforce an independent tunnel DTLS policy for each tunnel with a specific AR. it's giving individual vibes 🦋
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 is the total length in octets of the element, not counting the Type and Length fields 📏
- Reserved: a set of reserved bits for future use. every implementation that follows this protocol MUST set to 0 any bits that are reserved in the version of the protocol that implementation supports. Receivers MUST ignore all bits that aren't 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 the Access Router Information Element. in this context, each address in AR Information MUST be one of previously specified AR addresses 📍
the last element in Figure 14 that has no AR Information is the default tunnel DTLS policy. it covers any address that wasn't mentioned earlier, so the AR Information field here is optional (lowercase, no pressure!). if all ARs share the same tunnel DTLS policy, there won't be an AR Information field or its specific tunnel DTLS policy in this element 💅
5.3. IEEE 802.11 Tagging Mode Policy Element 🏷️
in IEEE 802.11 networks, the IEEE 802.11 Tagging Mode Policy Element is how the WTP decides to apply the QoS tagging policy when it receives packets from stations on a particular radio 📡 when the WTP sends packets out to the data channel toward the AR(s), those packets have to be tagged for QoS purposes (see [RFC5416]) ✨
the IEEE 802.11 Tagging Mode Policy follows the IEEE 802.11 WTP Quality of Service defined in Section 6.22 of [RFC5416] 🎀
same energy as before: if the AC gave 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 usually applied to all tunnels tied to 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 an 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 is the total length in octets of the element, not counting 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 how the AC tells 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 how the AC tells the WTP how 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 how the AC tells the WTP how DSCP QoS is to be enforced on the station's packet (inner) header (see [RFC5416]) 💜
- AR Information: this means the Access Router Information Element. in this context, each address in AR Information MUST be one of the previously specified AR addresses 📍
same deal as before: the last element in Figure 15 with no AR information is the default IEEE 802.11 Tagging Mode Policy. it covers any address that wasn't mentioned already, so the AR Information field here is optional. if all ARs share the same IEEE 802.11 Tagging Mode Policy, there won't be an AR Information field (or its specific policy) in this element 🫶
5.4. CAPWAP Transport Protocol Element 🚚
the CAPWAP data tunnel supports both UDP and UDP-Lite (see [RFC3828]) 🦋 when it runs over IPv4, UDP is used for the CAPWAP Data Channels. when it runs over IPv6, the CAPWAP Data Channel can use either UDP or UDP-Lite. the AC specifies and configures the WTP on which transport protocol to use for the CAPWAP data tunnel 👑
the CAPWAP Transport Protocol Element follows Section 4.6.14 of [RFC5415] ✨
and yep, the reliability plot twist is back: if the AC gave more than one AR address in the Access Router Information Element, the same CAPWAP Transport Protocol (the last one in Figure 16) is usually applied to every tunnel tied to those ARs. otherwise, CAPWAP Transport Protocol MUST be bonded together with each of the Access Router Information Elements, and the WTP will enforce an 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. the following enumerated values are supported:
- 1 - UDP-Lite: the UDP-Lite transport protocol is to be used for the CAPWAP Data Channel. heads up: this option MUST NOT be used if the CAPWAP Control Channel is being used over IPv4 and the AR address contained in the AR Information Element is an IPv4 address 🙅♀️
- 2 - UDP: the UDP transport protocol is to be used for the CAPWAP Data Channel 🌈
- AR Information: this means the Access Router Information Element. in this context, each address in AR information MUST be one of the previously specified AR addresses 📍
the last element in Figure 16 with no AR information is the default CAPWAP Transport Protocol. it covers any address that wasn't mentioned earlier, so the AR Information field here is optional. if all ARs share the same CAPWAP Transport Protocol, there won't be an AR Information field (or its specific transport) in this element 💀✨
5.5. GRE Key Element 🎀
okay so bestie, this is the element for GRE key stuff, and it's giving very "the WTP has to do the work" energy 💅
If a WTP receives the GRE Key Element in the Alternate Tunnel 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. Literally the key is how the AR knows which flow is which 🔑✨
The GRE Key Element field contains a 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. So multiple ARs can each get their own key, iykyk 🦋
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 ElementType: 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 4-octet number 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 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 🧚
okay this one is all about the MTU, the biggest packet size, and it's lowkey important 🌈
If AC has chosen a tunneling mechanism based on IPv6, it SHOULD support the minimum IPv6 MTU requirements [RFC8200]. This issue is described in [ARCH-TUNNELS]. AC SHOULD inform the WTP about the IPv6 MTU information in the Tunnel Info 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. Each AR can get its own MTU, no cap 🫶
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 ElementType: 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 2-octet number 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 📋
Per this document, IANA has registered the following values in the existing "CAPWAP Message Element Type" registry, defined in [RFC5415].
- 54: Supported Alternate Tunnel Encapsulations Type as defined in Section 3.1.
- 55: Alternate Tunnel Encapsulations Type as defined in Section 3.2.
- 1062: IEEE 802.11 WTP Alternate Tunnel Failure Indication as defined in Section 3.3.
Per this 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 0 through 6 and can be found in Section 3.2. Future allocations of values in this namespace are to be assigned by IANA using the "Specification Required" policy [RFC8126]. The registry format is given below. 🎀
Description 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 [TS.3GPP.29.281]Per this document, IANA has created a registry called "Alternate Tunnel 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 with the IEEE 802.11 WTP Alternate Tunnel Failure Indication message element as its sub-elements. These information elements contain a Type field. The namespace for the field is 16 bits (0-65535). This specification defines values 0 through 6 in Section 5. This namespace is managed by IANA, and assignments require an Expert 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 67. Security Considerations 😭🚨
okay bestie, security is SERIOUS, so read this one carefully 💀
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. 🔐🔥
8. References 📚
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>.8.2. Informative References
[ARCH-TUNNELS]
Touch, J. and M. Townsley, "IP Tunnels in the Internet
Architecture", Work in 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>.
[TS.3GPP.29.281]
3GPP, "General Packet Radio System (GPRS) Tunnelling
Protocol User Plane (GTPv1-U)", 3GPP TS 29.281, V13.1.0,
March 2016.Contributors 💖
okay bestie, the authors wanna give a big shoutout to 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 🫶✨ the whole list is giving main character energy, no cap.
Authors' Addresses 🦋
Here are the people who wrote this thing, with their mailing addresses and emails so you can slide into their DMs 💌
Rong Zhang 🌸
Rong Zhang
China Telecom
No.109 Zhongshandadao avenue
Guangzhou 510630
China
Email: zhangr@gsta.comRajesh S. Pazhyannur 💜
Rajesh S. Pazhyannur
Cisco
170 West Tasman Drive
San Jose, CA 95134
United States of America
Email: rpazhyan@cisco.comSri Gundavelli 🍓
Sri Gundavelli
Cisco
170 West Tasman Drive
San Jose, CA 95134
United States of America
Email: sgundave@cisco.comZhen Cao 🧚
Zhen Cao
Huawei
Xinxi Rd. 3
Beijing 100085
China
Email: zhencao.ietf@gmail.comHui Deng 🎀
Hui Deng
Huawei
Xinxi Rd. 3
Beijing 100085
China
Email: denghui02@gmail.comZongpeng Du 🌈
Zongpeng Du
Huawei
No.156 Beiqing Rd. Z-park, HaiDian District
Beijing 100095
China
Email: duzongpeng@huawei.com📦 where this page comes from
- ietf: rfc8350 2018-04
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms