CAPWAP Working Group B. O'Hara
Internet-Draft P. Calhoun
Expires: February 18, 2005 Airespace
J. Kempf
Docomo Labs USA
August 20, 2004
CAPWAP Problem Statement
draft-ietf-capwap-problem-statement-02
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Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
This document describes the Configuration and Provisioning for
Wireless Access Points (CAPWAP) problem statement.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 4
3. Security Considerations . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 6
Intellectual Property and Copyright Statements . . . . . . . . 8
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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 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 suprise to the networking community, since
similar limitations arose in the early 1980's 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.
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2. Problem Statement
The first problem introduced by large WLAN deployments is that 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, over the
devices in the network prior to the addition of the WLAN. 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 of
configuration from one AP to the next often leads to misconfiguration
and improper operation of the WLAN.
A second problem introduced by large WLAN deployments is distributing
and maintaining a consistent configuration throughout the entire set
of access points in the WLAN. 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 need to update dyanmic provisioning information in
all the APs in the WLAN require a prolonged phase-over time, while
each AP is updated and the WLAN does not have a single, consistent,
configuration.
A third problem introduced by large WLAN deployments is the
difficulty in dealing effectively with the dynamic nature of the WLAN
medium, itself. 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 performance for the WLAN to utilize
the wireless medium efficiently. 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 a significant amount of
time and effort.
A fourth problem introduced by large WLAN deployments is securing
access to the network and preventing installation of unauthorized
access points. Access points are often difficult to physically
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 the thief to obtain access to the resources
secured by those secrets.
Recently, multiple vendors have begun offering proprietary solutions
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that combine aspects of network switching, centralized control and
management, and distributed wireless access in a variety of new
architectures to adress some, or all, of the above mentioned
problems. Since interoperable solutions allow enterprises and
service providers a broader choice, a standardized, interoperable
interface between access points and a centralized controller
addressing the above mentioned problems seems desirable.
The physical portions of this network system, in currently fielded
devices, are one or more 802.11 access points (APs) and one or more
central control devices, alternatively described as controllers (or
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 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 description of detailed functional blocks, interfaces, and
information flow, will be reviewed by CAPWAP to determine if further
work is needed 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
utilizing a functional split between an access point and an access
controller.
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3. Security Considerations
The devices used in WLANs control the access to networks and provide
for the delivery of packets between hosts using the WLAN and other
hosts on the WLAN or elsewhere on the Internet. The functions for
control and provisioning of wireless access points, therefore require
protection to prevent misuse of the devices.
Requirements for central management, monitoring, and control of
wireless access points that should be addressed include
confidentiality, integrity, and authenticity. Once an AP and AC have
been authenticated to each other, it may not be sufficient that a
single level of authorization allows monitoring, as well as control
and provisioning. The requirement for more than a single level of
authorization should be determined. Physical security should also be
addressed, for those devices that contain security parameters that
are sensitive and might compromise the security of the system, if
those parameters were to fall into the hands of an attacker.
APs are often installed in locations that are difficult to secure, in
order to provide comprehensive radio coverage. 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 of 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
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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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