RFC7494
Internet Engineering Task Force (IETF) C. Shao Request for Comments: 7494 H. Deng Category: Standards Track China Mobile ISSN: 2070-1721 R. Pazhyannur
Cisco Systems
F. Bari
AT&T
R. Zhang
China Telecom
S. Matsushima
SoftBank Telecom
April 2015
IEEE 802.11 Medium Access Control (MAC) Profile for Control and
Provisioning of Wireless Access Points (CAPWAP)
Abstract
The Control and Provisioning of Wireless Access Points (CAPWAP) protocol binding for IEEE 802.11 defines two Medium Access Control (MAC) modes for IEEE 802.11 Wireless Transmission Points (WTPs): Split and Local MAC. In the Split MAC mode, the partitioning of encryption/decryption functions is not clearly defined. In the Split MAC mode description, IEEE 802.11 encryption is specified as located in either the Access Controller (AC) or the WTP, with no clear way for the AC to inform the WTP of where the encryption functionality should be located. This leads to interoperability issues, especially when the AC and WTP come from different vendors. To prevent interoperability issues, this specification defines an IEEE 802.11 MAC Profile message element in which each profile specifies an unambiguous division of encryption functionality between the WTP and AC.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc7494.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the document authors. All rights reserved.
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Contents
Introduction
The CAPWAP protocol supports two MAC modes of operation: Split and Local MAC, as described in RFC5415 and RFC5416. However, there are MAC functions that have not been clearly defined. For example, IEEE 802.11 [IEEE.802.11] encryption is specified as located in either the AC or the WTP with no clear way to negotiate where it should be located. Because different vendors have different definitions of the MAC mode, many MAC-layer functions are mapped differently to either the WTP or the AC by different vendors. Therefore, depending upon the vendor, the operators in their deployments have to perform different configurations based on implementation of the two modes by their vendor. If there is no clear specification, then operators will experience interoperability issues with WTPs and ACs from different vendors.
Figure 1 from RFC5416 illustrates how some functions are processed in different places in the Local MAC and Split MAC mode. Specifically, note that in the Split MAC mode, the IEEE 802.11 encryption/decryption is specified as WTP/AC, implying that it could be at either location. This is not an issue with Local MAC because encryption is always at the WTP.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Functions | Local MAC | Split MAC | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |Distribution Service | WTP/AC | AC | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |Integration Service | WTP | AC | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |Beacon Generation | WTP | WTP | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |Probe Response Generation| WTP | WTP | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Function |Power Mgmt/ | WTP | WTP | + |Packet Buffering | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |Fragmentation/ | WTP | WTP/AC | + |Defragmentation | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |Assoc/Disassoc/Reassoc | WTP/AC | AC | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |Classifying | WTP | AC | + IEEE +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 802.11 QoS |Scheduling | WTP | WTP/AC | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |Queuing | WTP | WTP | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |IEEE 802.1X/EAP | AC | AC | + IEEE +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 802.11 RSN |RSNA Key Management | AC | AC | + (WPA2) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |IEEE 802.11 | WTP | WTP/AC | + |Encryption/Decryption | | | |-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Note:
RSN - Robust Security Network RSNA - Robust Security Network Association WPA2 - Wi-Fi Protected Access 2
Figure 1: Functions in Local MAC and Split MAC
To solve this problem, this specification introduces the IEEE 802.11 MAC Profile. The IEEE 802.11 MAC Profile unambiguously specifies where the various MAC functionalities should be located.
IEEE MAC Profile Descriptions
A IEEE 802.11 MAC Profile refers to a description of how the MAC functionality is split between the WTP and AC shown in Figure 1.
Split MAC with WTP Encryption
The functional split for the Split MAC with WTP encryption is provided in Figure 2. This profile is similar to the Split MAC description in RFC5416, except that IEEE 802.11 encryption/ decryption is at the WTP. Note that fragmentation is always done at the same entity as the encryption. Consequently, in this profile fragmentation/defragmentation is also done only at the WTP. Note that scheduling functionality is denoted as WTP/AC. As explained in RFC5416, this means that the admission control component of IEEE 802.11 resides on the AC; the real-time scheduling and queuing functions are on the WTP.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Functions | Profile | | | 0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |Distribution Service | AC | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |Integration Service | AC | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |Beacon Generation | WTP | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |Probe Response Generation| WTP | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Function |Power Mgmt/ | WTP | + |Packet Buffering | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |Fragmentation/ | WTP | + |Defragmentation | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |Assoc/Disassoc/Reassoc | AC | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |Classifying | AC | + IEEE +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 802.11 QoS |Scheduling | WTP/AC | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |Queuing | WTP | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |IEEE 802.1X/EAP | AC | + IEEE +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 802.11 RSN |RSNA Key Management | AC | + (WPA2) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |IEEE 802.11 | WTP | + |Encryption/Decryption | | |-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Note: EAP - Extensible Authentication Protocol
Figure 2: Functions in Split MAC with WTP Encryption
Split MAC with AC Encryption
The functional split for the Split MAC with AC encryption is provided in Figure 3. This profile is similar to the Split MAC in RFC5416, except that IEEE 802.11 encryption/decryption is at the AC. Since fragmentation is always done at the same entity as the encryption, in this profile, AC does fragmentation/defragmentation.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Functions | Profile | | | 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |Distribution Service | AC | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |Integration Service | AC | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |Beacon Generation | WTP | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |Probe Response Generation| WTP | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Function |Power Mgmt/ | WTP | + |Packet Buffering | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |Fragmentation/ | AC | + |Defragmentation | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |Assoc/Disassoc/Reassoc | AC | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |Classifying | AC | + IEEE +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 802.11 QoS |Scheduling | WTP | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |Queuing | WTP | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |IEEE 802.1X/EAP | AC | + IEEE +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 802.11 RSN |RSNA Key Management | AC | + (WPA2) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |IEEE 802.11 | AC | + |Encryption/Decryption | | |-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Functions in Split MAC with AC encryption
IEEE 802.11 MAC Profile Frame Exchange
An example of message exchange using the IEEE 802.11 MAC Profile message element is shown in Figure 4. The WTP informs the AC of the various MAC Profiles it supports. This happens in either a Discovery Request message or the Join Request message. The AC determines the appropriate profile and configures the WTP with the profile while configuring the WLAN.
+-+-+-+-+-+-+ +-+-+-+-+-+-+
| WTP | | AC |
+-+-+-+-+-+-+ +-+-+-+-+-+-+
|Join Request[Supported IEEE 802.11 |
| MAC Profiles ] |
|---------------------------------------->|
| |
|Join Response |
|<----------------------------------------|
| |
|IEEE 802.11 WLAN Config. Request [ |
| IEEE 802.11 Add WLAN, |
| IEEE 802.11 MAC Profile |
| ] |
|<----------------------------------------|
| |
|IEEE 802.11 WLAN Config. Response |
|---------------------------------------->|
Figure 4: Message Exchange for Negotiating MAC Profiles
MAC Profile Message Element Definitions
IEEE 802.11 Supported MAC Profiles
The IEEE 802.11 Supported MAC Profile message element allows the WTP to communicate the profiles it supports. The Discovery Request message, Primary Discovery Request message, and Join Request message may include one such message element.
0 1 2 3
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0
+=+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| Num_Profiles | Profile_1 | Profile_[2..N]..
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Figure 5: IEEE 802.11 Supported MAC Profiles
o Type: 1060 for IEEE 802.11 Supported MAC Profiles
o Num_Profiles >=1: This refers to the number of profiles present in
this message element. There must be at least one profile.
o Profile: Each profile is identified by a value specified in
Section 3.2.
IEEE 802.11 MAC Profile
The IEEE 802.11 MAC Profile message element allows the AC to select a profile. This message element may be provided along with the IEEE 802.11 ADD WLAN message element while configuring a WLAN on the WTP.
0 1 2 3 4 5 6 7
+=+-+-+-+-+-+-+-+
| Profile |
+-+-+-+-+-+-+-+-+
Figure 6: IEEE 802.11 MAC Profile
o Type: 1061 for IEEE 802.11 MAC Profile
o Profile: The profile is identified by a value as given below
* 0: This refers to the IEEE 802.11 Split MAC Profile with WTP
encryption
* 1: This refers to the IEEE 802.11 Split MAC Profile with AC
encryption
Security Considerations
This document does not introduce any new security risks compared to RFC5416. The negotiation messages between the WTP and AC have origin authentication and data integrity. As a result, an attacker cannot interfere with the messages to force a less-secure mode choice. The security considerations described in RFC5416 apply here as well.
IANA Considerations
The following IANA actions have been completed.
o This specification defines two new message elements: IEEE 802.11
Supported MAC Profiles (described in Section 3.1) and the IEEE 802.11 MAC Profile (described in Section 3.2). These elements have been registered in the existing "CAPWAP Message Element Type" registry, defined in RFC5415.
CAPWAP Protocol Message Element Type Value
IEEE 802.11 Supported MAC Profiles 1060
IEEE 802.11 MAC Profile 1061
o The IEEE 802.11 Supported MAC Profiles message element and IEEE
802.11 MAC Profile message element include a Profile field (as defined in Section 3.2). The Profile field in the IEEE 802.11 Supported MAC Profiles denotes the MAC Profiles supported by the WTP. The Profile field in the IEEE 802.11 MAC Profile denotes the MAC Profile assigned to the WTP. The namespace for the field is 8 bits (0-255). This specification defines two values: zero (0) and one (1) as described below. The remaining values (2-255) are controlled and maintained by IANA, and the registration procedure is Expert Review RFC5226. IANA has created a new subregistry called "IEEE 802.11 Split MAC Profile" under the existing registry "Control And Provisioning of Wireless Access Points (CAPWAP) Parameters". The registry format is given below.
Profile Type Value Reference
Split MAC with WTP encryption 0 RFC 7494
Split MAC with AC encryption 1 RFC 7494
References
Normative References
[IEEE.802.11]
IEEE, "IEEE Standard for Information Technology -
Telecommunications and information exchange between
systems - Local and metropolitan area networks - Specific
requirements Part 11: Wireless LAN Medium Access Control
(MAC) and Physical Layer (PHY) Specifications", IEEE Std
802.11-2012, March 2012,
<http://standards.ieee.org/about/get/802/802.11.html>.
RFC5415 Calhoun, P., Ed., Montemurro, M., Ed., and D. Stanley,
Ed., "Control And Provisioning of Wireless Access Points
(CAPWAP) Protocol Specification", RFC 5415, March 2009,
<http://www.rfc-editor.org/info/rfc5415>.
RFC5416 Calhoun, P., Ed., Montemurro, M., Ed., and D. Stanley,
Ed., "Control and Provisioning of Wireless Access Points
(CAPWAP) Protocol Binding for IEEE 802.11", RFC 5416,
March 2009, <http://www.rfc-editor.org/info/rfc5416>.
Informative References
RFC5226 Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008, <http://www.rfc-editor.org/info/rfc5226>.
Acknowledgments
The authors are grateful for extremely valuable suggestions from Dorothy Stanley in developing this specification.
Guidance from the management team -- Melinda Shore, Scott Bradner, Chris Liljenstolpe, Benoit Claise, Joel Jaeggli, and Dan Romascanu -- is highly appreciated.
Contributors
Yifan Chen <[email protected]>
Naibao Zhou <[email protected]>
Authors' Addresses
Chunju Shao China Mobile No.32 Xuanwumen West Street Beijing 100053 China
EMail: [email protected]
Hui Deng China Mobile No.32 Xuanwumen West Street Beijing 100053 China
EMail: [email protected]
Rajesh S. Pazhyannur Cisco Systems 170 West Tasman Drive San Jose, CA 95134 United States
EMail: [email protected]
Farooq Bari AT&T 7277 164th Ave NE Redmond, WA 98052 United States
EMail: [email protected]
Rong Zhang China Telecom No.109 Zhongshandadao avenue Guangzhou 510630 China
EMail: [email protected]
Satoru Matsushima SoftBank Telecom 1-9-1 Higashi-Shinbashi, Munato-ku Tokyo Japan
EMail: [email protected]
