Wireless Access
Points
When the
ability to write and modify your own management software is the main
objective, custom-built Wireless Access Points are the way to go.
Take a look at what's involved in building a wireless bridge using
Linux, including software and hardware
considerations.
In this
article, we are discussing some very important points in Wireless
Access Points running Linux. We won't cover every last line of code,
every intermediate step, or every detail of hardware; that would
take a book and would be obsolete by the time you read it. Just few
simple points related to Wireless Access Points and to show you what
kinds of concerns and pitfalls you'll face should you want to do
this. Generally, we build the access point to operate as a bridge;
simply forwarding packets between the wireless network and a local
Ethernet. This allows wireless devices to simply be turned on and
attached using your existing network -- no new configuration, no
special routing.
The first is
flexibility and customizability. Want a firewall? No problem. Custom
routing? All easily managed. Custom Web-based configuration? Half an
hour's work with CGI scripts. You can add traffic graphing if you
like. That off-the-shelf box may have a special Windows-only
configuration tool, so it won't be possible to change your settings.
You won't be able to run your web log off of the Web server. If
there's a problem, you have to wait for a "firmware upgrade" --
which may or may not address your
problem.
The other, and
perhaps more compelling reason is that building Wireless Access
Points are fun, and it's a good way to learn about the issues you
may face running an embedded Linux system. Think of this as a
hobbyist's test project, and if you come up with a killer app for
it, you might just be able to make a profit anyway.
To follow the
whole thing, you'll also need another Linux box, to format and
configure the flash card. A laptop is ideal, but anything with a USB
port should work, if you have a CF reader that works under Linux. As
for software, there are existing packages that come pretty close to
working out of the box, or you could start from scratch with an old
set of install CDs and do it the hard way. This plan is broken into
phases; at the end of each phase, there are concrete, testable,
results. Each phase should be manageable within an hour or so of
playing around.
The phases of
building Wireless Access Points are:
- Initial
setup: We get the embedded system to boot and to offer a console
login prompt.
- Network
setup: We get the network up and running, so the machine can
actually be used as a functioning Wireless Access Points.
- Tweaking: We
start on the long road to changing and adapting our machine's
functionality.
Network setup:
What we really want, for Wireless Access Points, is a simple bridge;
packets from one network show up on the other network, nothing
special. The box isn't a router or a DHCP server or anything, it's
just a bridge. It could, of course, be set up as a DHCP server or
any of a dozen other things, but this is the easy way. A bridge will
simply send packets from the wire to the wireless and back. That
way, the Wireless Access Points device looks for all intents as
though it's simply attached to the physical network. Pebble Linux is
based on Debian, so that means playing around with
/etc/network/interfaces. A quick Google search yields a sample set
of commands to play with.
