Wireles Networks The Definitive Guide.pdf - Csbdu.in

Chapter 14. Using 802.11 Access Points
In even the simplest 802.11 network, proper configuration of the access points is essential. Without
properly configured network interfaces, no traffic will be bridged on to the wired network.
Access points can be divided into two groups. Home gateways and small office products are targeted
at price-conscious users and do not offer much in the way of functionality beyond simple connectivity.
Business-grade products are more expensive, but they possess functionality that is key to working with
larger networks containing multiple access points. This chapter takes a look at two access points
targeted at the high-end commercial user: the ORiNOCO AP-1000 and the Nokia A032. Extrapolating
low-end product administration from the basic set of tasks is straightforward.
The major tasks facing a network administrator are to connect the access point to the wired network,
configure the network interfaces, enable security features, and perform any configuration adjustments
necessary to tune the wireless network to the area in which it is deployed. This chapter assumes that
power and wired network connections are straightforward and have been taken care of.
14.1 General Functions of an Access Point
All access points provide a similar set of features to network users because the standard feature set is
specified by 802.11. Configuration of these features, of course, is vendor-specific, but the products are
fairly similar to each other.
Access points are bridges between the wireless world and the wired world. As bridges, then, all access
points have features that one would expect to see on a network bridge. They have at least two network
interfaces: a wireless interface that understands the details of 802.11 and a second interface to connect
to wired networks. To take advantage of the installed base and expertise, the wired interface is almost
always an Ethernet port. Many products also have a WAN port. Sometimes the WAN port is a serial
port that can be connected to a modem for use with a dial-up ISP account. It is also common to find
DSL interfaces in access points. Still, other access points add a second Ethernet port for connection to
a DSL modem or cable modem. Some access points have multiple wireless interfaces so network
managers can increase hot-spot capacity by using two interfaces on nonoverlapping channels. Many
access points also offer the option of using external antennas to further boost range and allow for finetuning
of antenna placement. Bridges have some buffer memory to hold frames as they are transferred
between the two interfaces, and they store MAC address associations for each port in a set of internal
tables.
Bridging tables are, of course, highly implementation-specific, and there is no guarantee of similarities
across the industry. Generally speaking, though, inexpensive consumer devices are fundamentally
designed with the assumption that they will be the sole access point for a network, while the more
expensive commercial devices include more advanced features to make large deployments and rollouts
easier. Commercial-grade devices are also designed to work cooperatively; the most common feature
is a vendor-proprietary Inter-Access Point Protocol (IAPP). An IAPP allows wireless stations to move
from access point to access point without interrupting link-layer connectivity. At this point, no
standard for an IAPP exists, though the 802.11 working group is addressing this shortcoming. (Some
cheaper products may support an IAPP, however.) Network management is generally much more
sophisticated on commercial-grade products to enable network engineers to manage the tens or
hundreds of devices used to create a large-scale coverage area.
All but the cheapest access points have a TCP/IP network interface. TCP/IP interfaces are intended for
remote management and typically accept only basic configurations; anything beyond an IP address,
netmask, and a single static default route is atypical. Depending on the level of sophistication of the
hardware and software, varying levels of low-level interface configuration are possible. Naturally, all
products allow the configuration of the network name. Other low-level parameters, however, may or
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