One document matched: draft-xue-opsawg-capwap-separation-capability-00.txt
Network Working Group L. Xue
Internet-Draft Z. Du
Intended status: Informational Huawei
D. Liu
China Mobile
R. Zhang
China Telecom
John Kaippallimalil
Huawei
July 10, 2013
Capability Announcement and AR Discovery in CAPWAP Control and Data
Channel Separation
draft-xue-opsawg-capwap-separation-capability-00
Abstract
In a centralized IEEE 802.11 Wireless Local Area Network (WLAN)
architecture, the Access Controller (AC) does not have the
intelligence to aggregate all the wireless frames. In addition,
increasing amounts of traffic handled by each access point would
require even more processing at an AC. Thus it is normal in an
existing operator's network for the WTPs to forward the wireless
frames directly to AR to avoid overloading the AC. In this scenario,
CAPWAP Control Channel and CAPWAP Data Channel are separated from
each other. This document provides extensions to CAPWAP for the
split scenario where CAPWAP Control and Data Channel are separated.
Requirements Language
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].
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/.
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
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material or to cite them other than as "work in progress."
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Split CAPWAP-CTL and CAPWAP-DATA Establishment . . . . . . . 3
2.1. AR Discovery . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Split Mode Capability Announcement . . . . . . . . . . . 4
3. CAPWAP Message Elements for Split Mode . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Normative References . . . . . . . . . . . . . . . . . . 7
6.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
In a centralized IEEE 802.11 Wireless Local Area Network (WLAN)
architecture, Control and Provisioning of Wireless Access Points
(CAPWAP) protocol is defined to enable Access Controller (AC) to
manage a collection of Wireless Termination Points (WTPs), specified
in [RFC5415] and [RFC5416]. In the existing specifications, CAPWAP
Control Channel and Data Channel between a WTP and AC are setup and
managed in a converged procedure. CAPWAP Control messages are
management messages exchanged between a WTP and AC; meanwhile, CAPWAP
data messages encapsulate forwarded wireless frames.
In practice, it is a general case in existing operator networks that
WTPs forward the wireless frames directly to AR to avoid overload on
the AC. This requirement is also mentioned in [I-D.cao-capwap-eap].
The AC does not have the intelligence to aggregate all the wireless
frames. In addition, increasing amounts of traffic handled by each
access point would require even more processing at an AC. In this
scenario, CAPWAP Control Channel and CAPWAP Data Channel should be
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separated from each other, as shown in the following figure.
CAPWAP-CTL +--------+
++========+ AC |
// +--------+
//
+-----+// CAPWAP-DATA +--------------+
| WTP |===========================| Access Router|
+-----+ +--------------+
Figure 1: Split CAPWAP Control and CAPWAP DATA Channel
However, up to now, there is only one common procedure for both
CAPWAP Control Channel and CAPWAP Data Channel setup [RFC5415]
between a WTP and AC. This is not sufficient if CAPWAP Control
Channel and CAPWAP Data Channel are split. This document extends
CAPWAP for applicability in split CAPWAP Control Channel and CAPWAP
Data Channel.
2. Split CAPWAP-CTL and CAPWAP-DATA Establishment
This section describes the session establishment process for split
CAPWAP Control Channel and CAPWAP Data Channel, called CAPWAP Split
Mode. In this architecture, the CAPWAP protocol should be concerned
with not only the interface between the WTP and the AC, but also the
interface between the WTP and the AR.
Using existing CAPWAP procedure [RFC5415] as the basis, additional
phases are needed, and these are specified in following sub sections.
2.1. AR Discovery
In CAPWAP Split Mode, AR discovery should be the Preliminary phase
for CAPWAP Data Channel procedures. The WTPs MUST obtain the AR
information, such as IP address which are used to establish the
CAPWAP Data Channel.
It is possible for the AR information to be configured manually on
the WTP. However, it is difficult to operate when there are large
numbers of WTPs in the network. An auto-configuration method is
required to enable AR discovery in larger networks. Several dynamic
methods such as DHCP or DNS could be used, but this document does not
discuss these methods in detail. It is also possible for AR Discovery
to be completed in the process of CAPWAP Control Channel procedures
defined in [RFC5415].
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A common deployment is for the AC and AR to be in a centralized
location in the operators network. In all cases, the AC can default
to acquiring AR information in the network via manual configuration.
After the Discovery Response messages received[RFC5415], a WTP can
select an AC with which to establish a secure DTLS session for CAPWAP
Control Channel. Then AC configures the WTP with AR address
appropriately via Configuration Status Response. When a WTP receives
the Configuration Status Response message carrying AR address, it
checks and restores the AR address for CAPWAP Data Channel.
In order to support AR discovery on a WTP, a new CAPWAP message
element, the AR Information Element is defined in section 3.
Additionally, the AR discovery process may also support load-sharing
and recovery from a single AR point of failure.
2.2. Split Mode Capability Announcement
In order to support CAPWAP Split Mode, the split mode capability MUST
be announced with agreement between a WTP and AC. Otherwise, the
CAPWAP Data messages will be sent to the AC instead of the AR, which
is not the expected outcome in split mode.
The CAPWAP Split Capability announcement can be achieved during Join
Operations [RFC5415] between a WTP and AC. A new CAPWAP message
element, the CAPWAP Mode Element is included in the Join Request
message and Join Response message between WTP and AC in order to
negotiate about the CAPWAP Mode. The element format is defined in
Section 3.
Besides, the decision about the CAPWAP mode between a WTP and AC can
be made based on operator requirements. For example, if the CAPWAP
Mode Element is included in either Join Request message or Join
Response message, or both are set to Split Mode value, CAPWAP will
operate in Split mode. Alternatively, the agreement that is
consistent with the value of CAPWAP Mode element carried in Join
Request messages send by WTP may be acceptable. This document does
not prescribe a single method to arrive at an agreement about the
CAPWAP mode.
3. CAPWAP Message Elements for Split Mode
As mentioned in earlier sections, two new CAPWAP message elements are
defined in this section for CAPWAP Split Mode.
The AR Information Element is used by the AC to configure the AR
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information to WTP. The format is as follows.
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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-------------------------------+
. AR Information .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
AR Information Element
Type: TBD
Length: >=8
AR Information: The IP address of AR served for WTP in the network.
In order to support load-sharing and recovery from a single AR point
of failure. The AR information can be formatted via TLV for sub-
elements, the sub-element format is:
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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-------------------------------+
| Prefer| AR Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| .
+-+-+-+-+
Load-sharing AR Information sub-element
Type: 1
Length; >= 9
AR Address: the IP address of AR served for WTP in the network.
The CAPWAP Mode element that is used for the split mode capability
MUST be announced with agreement between a WTP and AC. The format is
shown as follows.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-------------------------------+
| CAPWAP Mode | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
CAPWAP Mode Element
Type: TBD
Length: 8
CAPWAP Mode: If the value is 0, the CAPWAP operates in converged mode
defined in [RFC5415]. If the value is 1, the CAPWAP mode is split
mode, defined in this document.
Reserved: It can be used by operators to define the rule for making
CAPWAP mode decision.
4. IANA Considerations
This document defines two CAPWAP elements used in CAPWAP Split Mode.
IANA is requested to allocate the following type.
o The type for AR Information Element
o The type for CAPWAP Mode Element
5. Security Considerations
This document does not constrain the use of encryption mechanisms to
protect the data channel. If there are security requirements for
CAPWAP Data Channel, Datagram Transport Layer Security (DTLS)
[RFC4347] and the IPSec mechanism [RFC2401] can be used to guarantee
the security of the CAPWAP Data Channel.
If DTLS is used for CAPWAP Data Channel in CAPWAP Split Mode, the
DTLS procedure is required between a WTP and AR.
6. References
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6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2401] Kent, S. and R. Atkinson, "Security Architecture for the
Internet Protocol", RFC 2401, November 1998.
[RFC4347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security", RFC 4347, April 2006.
[RFC5415] Calhoun, P., Montemurro, M., and D. Stanley, "Control And
Provisioning of Wireless Access Points (CAPWAP) Protocol
Specification", RFC 5415, March 2009.
[RFC5416] Calhoun, P., Montemurro, M., and D. Stanley, "Control and
Provisioning of Wireless Access Points (CAPWAP) Protocol
Binding for IEEE 802.11", RFC 5416, March 2009.
6.2. Informative References
[I-D.cao-capwap-eap]
Zhang, R., Cao, Z., and H. Luo, "Encapsulation of EAP
Messages in CAPWAP Control Plane", draft-cao-capwap-eap-00
(work in progress), October 2012.
Authors' Addresses
Li Xue
Huawei
No.156 Beiqing Rd. Z-park, Shi-Chuang-Ke-Ji-Shi-Fan-Yuan,
HaiDian District
Beijing 100095
China
Email: xueli@huawei.com
Zongpeng Du
Huawei
No.156 Beiqing Rd. Z-park, Shi-Chuang-Ke-Ji-Shi-Fan-Yuan,
HaiDian District
Beijing 100095
China
Email: duzongpeng@huawei.com
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Dapeng Liu
China Mobile
Unit 2, 28 Xuanwumenxi Ave, Xuanwu District
Beijing 100053
China
Email: liudapeng@chinamobile.com
Rong Zhang
China Telecom
No. 109 Zhongshandadao avenue
Guangzhou 510630
China
Email: zhangr@gsta.com
John Kaippallimalil
Huawei
5430 Legacy Drive, Suite 175
Plano TX 75024
Email: john.kaippallimalil@huawei.com
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