Configuration and Provisioning for Wireless Access Points (CAPWAP)

Problem Statement

Status of This Memo

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Copyright Notice

Copyright © The Internet Society (2005).

Abstract

This document describes the Configuration and Provisioning for Wireless Access Points (CAPWAP) problem statement.

1. Introduction

With the approval of the 802.11 standard by the IEEE in 1997, wireless LANs (WLANs) began a slow entry into enterprise networks. The limited data rates of the original 802.11 standard, only 1 and 2 Mbps, limited the widespread adoption of the technology. 802.11 found wide deployment in vertical applications, such as inventory management, point of sale, and transportation management. Pioneering enterprises began to deploy 802.11, mostly for experimentation.

In 1999, the IEEE approved the 802.11a and 802.11b amendments to the base standard, increasing the available data rate to 54 and 11 Mbps, respectively, and expanding to a new radio band. This removed one of the significant factors holding back adoption of 802.11 in large enterprise networks. These large deployments were bound by the definition and functionality of an 802.11 Access Point (AP), as described in the 802.11 standard. The techniques required extensive use of layer 2 bridging and widespread VLANs to ensure the proper operation of higher layer protocols. Deployments of 802.11 WLANs as large as several thousand APs have been described.

Large deployments of 802.11 WLANs have introduced several problems that require solutions. The limitations on the scalability of bridging should come as no surprise to the networking community, as similar limitations arose in the early 1980s for wired network bridging during the expansion and interconnection of wired local area networks. This document will describe the problems introduced by the large-scale deployment of 802.11 WLANs in enterprise networks.

2. Problem Statement

Large WLAN deployments introduce several problems. First, each AP is an IP-addressable device requiring management, monitoring, and control. Deployment of a large WLAN will typically double the number of network infrastructure devices that require management. This presents a significant additional burden to the network administration resources and is often a hurdle to adoption of wireless technologies, particularly because the configuration of each access point is nearly identical to the next. This near-sameness often leads to misconfiguration and improper operation of the WLAN.

Second, distributing and maintaining a consistent configuration throughout the entire set of access points in the WLAN is problematic. Access point configuration consists of both long-term static information (such as addressing and hardware settings) and more dynamic provisioning information (such as individual WLAN settings and security parameters). Large WLAN installations that have to update dynamic provisioning information in all the APs in the WLAN require a prolonged phase-over time. As each AP is updated, the WLAN will not have a single, consistent configuration.

Third, dealing effectively with the dynamic nature of the WLAN medium itself is difficult. Due to the shared nature of the wireless medium (shared with APs in the same WLAN, with APs in other WLANs, and with devices that are not APs at all), parameters controlling the wireless medium on each AP must be monitored frequently and modified in a coordinated fashion to maximize WLAN performance. This must be coordinated among all the access points, to minimize the interference of one access point with its neighbors. Manually monitoring these metrics and determining a new, optimum configuration for the parameters related to the wireless medium is a task that takes significant time and effort.

Fourth, securing access to the network and preventing installation of unauthorized access points is challenging. Physical locations for access points are often difficult to secure since their location must often be outside of a locked network closet or server room. Theft of an access point, with its embedded secrets, allows a thief to obtain access to the resources secured by those secrets.

Recently, to address some, or all, of the above problems, multiple vendors have begun offering proprietary solutions that combine aspects of network switching, centralized control and management, and distributed wireless access in a variety of new architectures. Since interoperable solutions allow enterprises and service providers a broader choice, a standardized, interoperable interface between access points and a centralized controller addressing the problems seems desirable.

In currently fielded devices, the physical portions of this network system are one or more 802.11 access points (APs) and one or more central control devices, alternatively described as controllers (or as access controllers, ACs). Ideally, a network designer would be able to choose one or more vendors for the APs and one or more vendors for the central control devices in sufficient numbers to design a network with 802.11 wireless access to meet the designer's requirements.

Current implementations are proprietary and are not interoperable. This is due to a number of factors, including the disparate architectural choices made by the various manufacturers. A taxonomy of the architectures employed in the existing products in the market will provide the basis of an output document to be provided to the IEEE 802.11 Working Group. This taxonomy will be utilized by the 802.11 Working Group as input to their task of defining the functional architecture of an access point. The functional architecture, including descriptions of detailed functional blocks, interfaces, and information flow, will be reviewed by CAPWAP to determine if further work is necessary to apply or develop standard protocols providing for multi-vendor interoperable implementations of WLANs built from devices that adhere to the newly appearing hierarchical architecture using a functional split between an access point and an access controller.

3. Security Considerations

The devices used in WLANs control network access and provide for the delivery of packets between hosts using the WLAN and other hosts on the WLAN or elsewhere on the Internet. Therefore, the functions for control and provisioning of wireless access points, require protection to prevent misuse of the devices.

Confidentiality, integrity, and authenticity requirements should address central management, monitoring, and control of wireless access points that should be addressed. Once an AP and AC have been authenticated to each other, a single level of authorization allowing monitoring, control, and provisioning may not be sufficient. The requirement for more than a single level of authorization should be determined. Physical security should also be addressed for those devices that contain sensitive security parameters that might compromise the security of the system, if those parameters were to fall into the hands of an attacker.

To provide comprehensive radio coverage, APs are often installed in locations that are difficult to secure. The CAPWAP architecture may reduce the consequences of a stolen AP. If high-value secrets, such as a RADIUS shared secret, are stored in the AC, then the physical loss of an AP does not compromise these secrets. Further, the AC can easily be located in a physically secure location. Of course, concentrating all the high-value secrets in one place makes the AC an attractive target, and strict physical, procedural, and technical controls are needed to protect the secrets.

Authors' Addresses

   Bob O'Hara
   Airespace
   110 Nortech Parkway
   San Jose, CA  95134
   
   Phone: +1 408-635-2025
   EMail: bob@airespace.com
   
   Pat R. Calhoun
   Airespace
   110 Nortech Parkway
   San Jose, CA  95134
   
   Phone: +1 408-635-2000
   EMail: pcalhoun@airespace.com
   
   James Kempf
   Docomo Labs USA
   181 Metro Drive, Suite 300
   San Jose, CA  95110
   
   Phone: +1 408 451 4711
   EMail: kempf@docomolabs-usa.com

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