Wireless Howto
Roberto Arcomano berto@fatamorgana.com
v1.6 - July 31, 2002
Wireless is a new technology in networking cards, with high speed rate
(up to 11 Mbps). This document explains how to setup Wireless in
Linux, compatibility problems, something about geographic requirements
and more. Latest release of this document can be found at
http://www.fatamorgana.com/bertolinux <http://www.fatamor
gana.com/bertolinux>
______________________________________________________________________
Table of Contents
1. Introduction
1.1 Introduction
1.2 Copyright
1.3 Translations
1.4 Credits
2. Background Knowledge
2.1 What about Wireless?
2.2 What's the max distance between radio cards?
2.3 What's the difference between wired and Wireless network?
2.4 What I need to know to setup a Wireless network?
2.5 Why should I setup a Wireless network and what I expect from it?
2.6 What Wireless cards are covered by this howto?
2.7 How much do they cost?
3. Technical info about Wireless
3.1 Physical Layer
3.2 Configurations
3.3 Compatibility
3.4 Should I use Adhoc or Infrastructure?
3.5 A Linux Box cannot act as an AccessPoint?
4. Toolbox required
4.1 Hardware requirement
4.2 Software requirement
5. Overview on Wireless network setup.
5.1 Fundamental steps
5.2 Low Level Kernel Config
5.3 Data-link level setting
5.4 Ip setting
5.4.1 A simple configuration
5.4.2 A more complex configuration
5.4.3 Internet Access
5.4.4 Mixed network: Wired and Wireless
6. Setup
6.1 General setup info
6.2 Proxim Symphony
6.3 Webgear Aviator 2.4 and AviatorPro
6.4 Lucent Wavelan I, II, Orinoco products and Cabletron
6.5 YDI
7. More about Wireless
7.1 A Wireless Linux distribution
8. Useful links
8.1 Open software link
8.2 Commercial link
9. FAQ - Frequently asked questions
10. Appendix A - Netmask 255.255.255.255, proxy arp and bridging
11. Appendix B - Siemens DECT Radio Modem
______________________________________________________________________
1. Introduction
1.1. Introduction
This document explains something about Wireless networking, how to
setup it, problems with it. Unliked wired network, Wireless requires
some additional trick to work well. You should know something about
antennas, pointing it, roaming info and so on. Feedback are welcome.
You can found more interesting help at Jean Tourrilhes Wireless Howto
<http://www.hpl.hp.com/personal/Jean_Tourrilhes/Linux>
For any suggestion and feedback write to my email address
<mailto:berto@fatamorgana.com>
1.2. Copyright
Copyright (C) 2000,2001 Roberto Arcomano.
This document is free; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free
Software Foundation; either version 2 of the License, or (at your
option) any later version.
This document is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details. You can get a copy of the
GNU GPL here <http://www.gnu.org/copyleft/gpl.html>
1.3. Translations
If you want to translate this document you are free, you only have to:
1. Check that another version of it doesn't already exist at your
local LDP
2. Maintain all 'Introduction' section (including 'Introduction',
'Copyright',
Warning! You don't have to translate TXT or HTML file, you have to
modify LYX file, so that it is possible to convert it all other
formats (TXT, HTML, RIFF, etc.): to do that you can use "LyX"
application you download from http://www.lyx.org <http://www.lyx.org>.
No need to ask me to translate! You just have to let me know (if you
want) about your translation.
Thank you for your translation!
1.4. Credits
Thanks to Fatamorgana Computers <http://www.fatamorgana.com> for
hardware equipment and experimental opportunity.
Thanks to Linux Documentation Project <http://www.linuxdoc.org> for
publishing and uploading my document in a very quickly fashion.
2. Background Knowledge
2.1. What about Wireless?
Wireless is a new technology that can help you to connect computers at
distance. It works with Wireless cards with a TX/RX inside at 2.4 GHz
while the software interface is Ethernet-like, with an hardware
address different for each card in the world. Typical transmit power
is 10-20 mW till 100mW (see standard IEEE 802.11 and FCC/CEPT
licenses).
2.2. What's the max distance between radio cards?
The most important thing in Wireless communications is the line of
sight clear: you MUST SEE (with eyes or with a binocular) the antenna
from the other end or you can have (at most) a little tree between
them.
The distance depends on the antenna and (eventually amplifier) used:
2-300 meters with a omnidirectional antenna; 1 km with a directive
one; 2-3 km with a omnidirectional amplified (200mW); some km with
parabolic antenna. 50-60 km with parabolic or directive antenna
amplified (some Watts).
Be aware that it is not always legal to amplifier Wireless cards,
cause you could violate FCC/CEPT (and also your country relative)
specifics.
2.3. What's the difference between wired and Wireless network?
Wired networks are very simple to setup (at least at low level).
Wireless networks are very difficult to setup, to manage, to debug...
Typical problem with wired networks like hardware install, software
install, debug and so on become very critical with Wireless:
1. You have to choose the right Wireless card: there are many cards
from many vendor with many requirement and specs. If you want to
create a little LAN/WAN you have to buy IEEE 802.11 compliant
Wireless cards with an Access Point.
2. Many cards are PCMCIA, so you have to install pcmcia Linux source
first.
3. You have to test it with 2 running systems, first at very short
distance, then you can get far.
4. You should test it at any weather (typically rain).
5. Finally be happy for setting up.
If you installed a repeater (Linux box that has many Wireless and
wired cards) you may have problem editing its configuration at
distance!
2.4. What I need to know to setup a Wireless network?
There are a number of requirement to setup a Wireless network;
software requirement:
1. Generic network knowledge like IP address, netmask, routing...
covered by generic Linux NET3-4-HOWTO; *
2. Specific network knowledge like proxy arp, bridging, proc fs,
contained in Proxy-ARP-Subnet, Bridge Mini-Howto and in Linux
Kernel Source (2.2.x or 2.4.x) under Documentation/networking/ ip-
sysctl.txt) *
3. Wireless network knowledge like access mode (ADHOC, INFRASTRUCTURE
and ACCESS POINT), channel concept, outdoor and indoor defines and
so on that you can find in any document concerning Wireless: IEEE
standard 802.11, CEPT, etc.
non software requirement:
1. Minimal experience in antennas, physical mounting, pointing
2. Pc hardware installation with particular attention to not produce
interference between different Wireless Cards (if required).
finally a great luck!
* All Howtos needed by this document can be retrieved from
http://www.linuxdoc.org <http://www.linuxdoc.org>
2.5. Why should I setup a Wireless network and what I expect from it?
Why? Because you're not satisfied of wired network!
With Wireless cards you can go across garden, parks, houses, (but you
MUST SEE the other end!).
High Level Protocol used in Wireless Cards are the same used in
Ethernet cards: TCP/IP over Wireless Ethernet-like but make attention
to Windows Sharing Application, cause if you use Linux to forward, you
are warned that a ip forwarder doesn't let pass through broadcast
messages (see more on NetBIOS protocol): in this case you should use a
WINS server to support Network Browsing (see Samba doc).
Wireless let you create a little LAN/WAN with a central point of
access (maybe with Internet Access!) and give access to anyone by air!
Imagine a country all cabled by radio machines.
Imagine a network that can connect all country people together,
sharing files, audio applications, video applications at high
bandwidth (like cable network).
All that can be done (and it's already done in some country) using
Wireless cards with Wireless Access Point and Wireless Linux Boxes
that can operate as repeater (at IP level such as router or, if you
want, at data-link level, with bridge driver, see more at Bridge Http
Link <http://openrock.net/bridge> or Bridge Ftp Link
<ftp://openrock.net/bridge>
2.6. What Wireless cards are covered by this howto?
In this howto I start with a generic configuration (to introduce
Wireless networking), then I describe an example for each card I knew
directly, with some trick you can use to improve its performance.
Wireless Card list:
1. Proxim Symphony -http://www.proxim.com
2. Webgear AviatorPRO 2.4 (pcmcia support needed) -
http://www.webgear.com
3. Lucent Wavelan I, II, Orinoco - http://www.lucent.com and
http://www.orinocowireless.com <http://www.orinocowireless.com>
4. Cabletron - http://www.cabletron.com
5. YDI am930_isa - http://www.ydi.com
6. Siemens Radio Modem (Dect) - http://www.siemens.com
7. RadioLan (5 GHZ) - http://www.radiolan.com
For a very more exhaustive list see Jean Tourrilhes Wireless Howto.
Siemens Radio Modem is not a really 802.11 Wireless card, they are
modems that you can attach to serial and they act as modem (at 1800
MHz, so DECT technology). Appendix B describe their use.
RadioLan cards work at 5.4GHz in a Windows 9x environment and with a
RadioLan Access Point that bridges between Wired and Wireless networks
(there are no Linux driver as I know).
2.7. How much do they cost?
Wireless cards listed above are very low expansive: they start from
very few hundred of dollars up to some thousand of dollars for Access
Point that have 2 Wireless card (Lucent, for example) that can act as
a bridge.
3. Technical info about Wireless
Here I report some technical info to understand basic Wireless
environment.
3.1. Physical Layer
At first layer ISO/OSI we can have 3 kind of spec:
1. FHSS, Frequency Hopping Spread Spectrum
2. DSSS, Direct Sequence Spread Spectrum
3. Infrared connections, not covered by this howto
3.2. Configurations
2 types of configurations:
1. AdHoc mode (also called Independent mode), where you have
independent networks with a BSS (Basic Service Set) each one. Each
station has the same BSS.
2. Infrastructure mode, where a number of networks (with a BSS each
one) can communicate each other by means of an Access Point (one
for each BSS) to create a ESS (Extended Service Set). Also there is
a roaming function letting a station "attach" to the nearer Access
Point.
Adhoc is the simpler method (and the also the less scalable) and let
many hosts communicate each other directly. The restrictive
requirement is that all one are to be visible directly to reach a
complete coverage of the network. (at least Ideally, because this
problem could be solved at IP level! For more see Par 5.4).
Adhoc mode
A - - - - - C
\ /
| \ / |
/\
| / \ |
/ \
B - - - - - D
In a Infrastructure environment you use the Access Point to which ALL
other hosts must connect to share the network.
Infrastructure mode
ESS
A - - - | - Access Point - - Access Point - | - - - D
B - - - | BSS1 BSS2 | - - - E
C - - - | | - - - F
B and C could not see D,E and F, but they can communicate as well
cause all one are using the same ESS. Important: A,B and C could also
not see each other.
In addition there are terms like indoor and outdoor to distinguish
short area coverage from long area coverage.
3.3. Compatibility
Keep on mind that there are a number of Wireless cards in the world,
but not every card can communicate with every other one. For talking
together the cards have to use to:
1. same configuration mode: all Adhoc or all Infrastructure
2. same physical layer: all DSSS or all FHSS
3. same protocol (for example Proxim has its particular proprietary
protocol OpenAir that cannot talk with other FHSS cards).
3.4. Should I use Adhoc or Infrastructure?
Access Point are very useful and killing problem but they are
expansive. Ideally, for a more concentrated network you could use
Infrastructure mode, while for few hosts you can choose Adhoc: why to
spend much money for few hosts?
Anyway be aware that if you spend much money probably all works well
while spending less you could have some trouble.
3.5. A Linux Box cannot act as an AccessPoint?
Good asking!
Recently there is a kind of hardware that allows this feature: Prism2
You can find something at http://people.ssh.com/jkm/Prism2/
<http://people.ssh.com/jkm/Prism2/>
4. Toolbox required
4.1. Hardware requirement
You need a Linux Box (486 or, better, a Pentium 100+ with 16MB+ ram),
the Wireless network card, an antenna (see par 2.2). You need the same
on the other end (with Win9x or WinNT, if you prefer...) cause you
have to simulate a communication!
4.2. Software requirement
You need:
1. recent stable kernel sources (2.2.x)
2. recent stable pcmcia sources (pcmcia-cs) if you bought a pcmcia
card
3. Wireless network driver: if you don't have it you can download it
from the vendor web site or the card manufacturer web site. If you
don't find it you can search at Jean Tourrilhes Wireless Howto.
If you don't find even here you probably have to wait or to convert a
Windows driver to a Linux driver!! (good luck!).
After that, you have to recompile your kernel, recompile your pcmcia
source (if need by the Wireless card), finally recompile your Wireless
driver. That is the generic situation, maybe for some card you have to
perform step 3 only or 1 and 3, it depends on specific driver.
5. Overview on Wireless network setup.
5.1. Fundamental steps
Once you have got the needed material and you have compiled all the
needed you should do the fundamental step in a Wireless configuration:
1. Low level kernel config Let the Linux Kernel see your Wireless card
(at low level, such as ioport, interrupts, dma...): you must see
some kind of kernel message that advertise you that Wireless card
has been right found and configured.
2. Data-link level setting For each particular Wireless card there is
an utility that can set typical Wireless data-link level value. For
example in Proxim Symphony the utility is called "rl2cfg" while in
pcmcia cards settings are in pcmcia config files. You have to set
all your Wireless cards with coherence to make them talk together.
3. Ip setting Now you should be able to use ifconfig and route
capabilities to change IP settings.
4. Tricks for better performance and to a avoiding conflicts. Now your
Wireless Network is basically working: in addition you have to
adjust some particular setting like proxy-arp, icmp echo redirect,
bridging, channel change and so on to optimize your network and
avoiding strange and bandwidth killing conflicts
N.B.: step 1, 2 and 3 correspond to level 1, 2 and 3 of standard
ISO/OSI, while step 4 is an addendum to solve situation generated by
netmask 255.255.255.255. In fact 32 bit netmask violates standard
ISO/OSI cause the network force to use the same address for broadcast
and ip machine and the network address doesn't exist.
Someone could criticize this point of view, but if you use the
standard ISO/OSI to configure Wireless network with you'll loss many
ones configuring subnets; for each subnet usually you discard 2 IP
number (Network and broadcast) and you cannot achieve the flexibility
on IP assigning (geographically kind). You can find more on Appendix
A about this.
You could notice that step 2 is not present in Wired cards cause
there's no particular settings to do there.
5.2. Low Level Kernel Config
Always it's a problem for Pc administration: to let kernel (or in
general) see your hardware.
Wireless cards are more complex because many of them usually have a
Pcmcia plug, so first of all you have to let your kernel see Pcmcia
adapter card, then you can try to install specific hardware driver for
your Wireless card.
So, in Pcmcia config you have to:
1. install linux kernel source, from http://www.kernel.org to
/usr/src/linux (see tar and gzip utilities)
2. install linux pcmcia source, from
ftp://projects.sourceforge.net/pub/pcmcia-cs to install to
/usr/src/pcmcia (see tar and gzip utilities)
3. config and recompile your kernel: read file README in your linux
directory (/usr/src/linux)
4. config and recompile your pcmcia source: under /usr/src/pcmcia use
configure and make. Be sure your driver is here, else your have to
install it following driver instructions (usually a tar zxvf
driver.tgz under pcmcia dir is sufficient). After type "make all"
to compile. At the end type "make install".
5. After typed install you'll find some useful config files under
/etc/pcmcia .
In non pcmcia case:
1. If your driver is present (99% not) under linux sources, you have
to install it in a directory, then to compile it.
Once you know module name you have to load it: in pcmcia config you
only need to start pcmcia daemon (/etc/rc.d/init.d/pcmcia start for
RedHat), for other "modprobe module_name options". With options you'll
give ioport, irq and data-link settings (see Par 5.3) to Wireless
driver. Anyway your useful tools to know if hardware has correctly
been seen by driver are:
1. "tail /var/log/messages" that explains info about syslog
2. "dmesg" for more info.
3. /proc dir: ioports, devices, irq files and driver specific sub-
directories.
5.3. Data-link level setting
What is that?
Wired networks need only to connect each other and then you'll be able
to set TCP/IP parameters.
In opposite Wireless networks need data-link settings, such as:
1. What kind of Wireless network I belong to? (Adhoc or
Infrastructure)
2. What channel I have to use?
3. What subnet (BSSID) I belong to, what is my ESS ID?
4. Is my communication protected by such a encryption algorithm?
Length key?
As you see there are many settings you have to adjust, the reason come
from the architecture of Wireless network: there could be someone, in
near distance, that could see your packets, use your services only
pointing his antenna on the right direction and setting up right
TCP/IP parameters.
In addition there could be many Wireless subnets that could generate
interference each other.
So here are:
1. Options at load-time module: "modprobe ray_cs essid='LINUX'" for
example or
2. Utilities at run-time driver: "rl2cfg eth1 master".
5.4. Ip setting
This is the third problem you have to face. Here situation become
problematic only when your network begin to evolve in a bigger one.
Remember Wireless IP Networking doesn't stress you if you don't stress it!
5.4.1. A simple configuration
All the hosts view each other
A - - - - - C
\ /
| \ / |
/\
| / \ |
/ \
B - - - - - D
A configuration like this is very simple and don't require nothing
special (at Ip level): you only need to assign an IP address for each
host and to assign a coherent global netmask.
5.4.2. A more complex configuration
A doesn't see B directly
A <- - - -
NO\ |
TALK\ C
\ |
B <- - - -
Here A and B can communicate only passing through C.
If the network is in Infrastructure mode and C is the Access Point all
is ok. In Adhoc mode you also can design a host to "master" capability
(I know the term is not so formal!), a host that creates a BSS and to
which any other host can join that BSS.
Full connectivity now is reached at IP level: A and B talk to C using
the same C interface, so if you try to ping from A to B you'll receive
many ICMP REDIRECT packets from C, cause C is telling A that the
destination is already in the network from which come the request.
Solution: type a "echo 0 >
/proc/sys/net/ipv4/conf/ethx/send_redirects" (where ethx is the
interface on C towards A and C) to null all that.
Another problem: what netmask I assign to A and C? If you assign a
netmask to A that include A and C nothing works because A don't use
the gateway (C) but make the ARP request with unknown destination MAC
address.
You could think to use proxy arp, but without effect cause proxy arp
reply to source only when the destination is in a different interface
from the source: this is not the case!!
So you have to set a very little netmask (Win9x let it be
255.255.255.254, WinNT at least 255.255.255.248), and you have to
assure that hosts A and C don't have the same net address.
Examples:
1. IP(A) = x.y.z.2/31, IP(B) = x.y.z.3/31. This doesn't work cause A
asks for B in its network (ARP request) and C doesn't answer cause,
for it, A and B belong to the same interface (so, no proxy arp).
2. IP(A) = x.y.z.1/31, IP(B)= x.y.z.2/31. This works cause A ask to C
(send requests to B with C MAC address) for B.
In general with a netmask 255.255.255.254 system works with 2 IP
changing only for the final bit.
All that is a TCP/IP forcing but is the only method to obtain an high
level of flexibility.
Note: If you use an Access Point (network in Infrastructure mode) you
haven't redirect problem, cause all is solved at data-link level
(almost every Access Point acts as a bridge...). But Access Point are
expansive (about 1000 USD or more) and it is more economic to use a
P133 32MB Ram to forward, even with 2 or more cards.
5.4.3. Internet Access
A - - - - - C - - Internet
\ /
| \ / |
/\
| / \ |
/ \
B - - - - - D
There is a number of situation:
1. C is the only Public IP address. You only have to set private IP
address (192.168.x.y for example) for the Wireless network
enabling, on C, forwarding and masquering. A, B and D will have C
as default GW.
2. You have a public netmask visible from Internet and C is your
default GW to Internet for the network. You only need to enable
forwarding on C, setting up default GW on A, B and D to point to C.
3. You have a public netmask visible from Internet and C is not the
default GW to Internet. You have 2 possible solutions: Modify your
default GW to let it point to C for your network. Symmetrically you
have to let C point to default GW to go to Internet. You could,
instead, enable proxy arp feature to C (echo 1 >
/proc/sys/net/ipv4/conf/ethx/proxy_arp where ethx is the interface
towards the default GW) and set your default GW on C to point to
the default GW. Proxy arp is a TCP/IP forcing but works well.
5.4.4. Mixed network: Wired and Wireless
Internet
\
\ E
\ /
\ / Wireless
A - - - - - C - - F
\ / \
| \ / | \
Wired /\ G
| / \ |
/ \
B - - - - - D
Now C joins 2 networks: on the right Wireless and Wired on the left.
More you have Internet Access, so in total you have 3 network cards in
C.
What IP Address I assign to hosts? You have 2 possible solutions:
1. Split up network in 2 subnets: for example 192.168.1.0/24 and
192.168.2.0/24. This solution is quickly but is not scalable if
you are using Internet IP addresses cause you have to drop too many
IPs.
2. Enable Proxy Arp feature to C for all 2 interfaces. Network
parameters (net address and netmask) are the same for Wireless and
Wired, but with proxy-arp enabled I can choose which IPs are on
Wired and which on Wireless.
Now we examine solution 2
For example: Consider you have Internet public subnet x.y.z.0/24.
Interfaces are:
1. ifconfig eth0 x.y.z.C netmask 255.255.255.255 (Wired)
2. ifconfig eth1 x.y.z.C netmask 255.255.255.255 (Wireless)
3. ifconfig eth2 x.y.z.C netmask 255.255.255.255 (to Internet)
Static routes on eth2:
1. route add IPGW dev eth2
2. route add default gw IPGW
This route stands for addressing all Internet requests to your Default
GW: as you notice, first you have to tell Linux where is the router,
then let default requesting through it.
Static routes on eth0:
1. route add x.y.z.A dev eth0
2. route add x.y.z.B dev eth0
3. route add x.y.z.D dev eth0
Hosts A,B and D on the Wired Network
Static routes on eth1:
1. route add x.y.z.E dev eth1
2. route add x.y.z.F dev eth1
3. route add x.y.z.G dev eth1
Hosts E,F and G on the Wireless Network
Note that flexibility is very high, but you have to manual set each
host.
6. Setup
Here I report some examples (I hope useful!) on how to configure more
diffuse and not expansive Wireless Cards.
6.1. General setup info
Wireless cards have interface similar to any Ethernet cards, so you
have to add in /etc/conf.modules:
1. "alias ethx module", where ethx is the interface you want to assign
to your wireless card and module is name of kernel module.
2. "options module io=0xAAA irq=I ...", where 0xAAA is the io base
address to assign the card, I is the IRQ and so on if there are
other parameters.
After this you'll be able to use ifconfig and route commands to
configure your card at IP level.
6.2. Proxim Symphony
Network type: FHSS, Adhoc only and with proprietary protocol OpenAir.
Web site:http://www.proxim.com where you need to download
documentation and driver for Linux and Win9x.
Drivers come with source code to compile:
1. untar it in a empty directory
2. type make for help.
3. make modules; make modules_install to install the driver rlmod.o
and the utility rl2cfg.
4. to run the driver (after modified /etc/conf.modules: see Par.6.1.)
you only need to turn up the interface with ifconfig command.
Utility rl2cfg (for help type man rl2cfg once done c step) let you
change typical data-link level settings:
1. "rl2cfg dev ethx sta" to set it to station (Slave)
2. "rl2cfg dev ethx msta" to set it to master station (Master)
3. "rl2cfg dev ethx alt" to set it to automatically mode
This is all you have to know to get it properly working.
6.3. Webgear Aviator 2.4 and AviatorPro
Network type: FHSS, Adhoc only for Aviator 2.4 and Infrastructure for
AviatorPro.
These cards need more for working, because you have to compile Pcmcia
source as they come with Pcmcia plug.
Web site is http://www.webgear.com.
To configure:
1. You have to download source pcmcia and to expand it to
/usr/src/pcmcia (see Par 5.2)
2. Download driver form http://www.webgear.com and type "tar zxvf
driver.tgz" in /usr/src/pcmcia directory.
3. reconfig pcmcia (see Par 5.2)
4. Following instructions you have to append to file
/etc/pcmcia/config.opts entry "source ./ray_cs.opts".
5. Note that in /etc/pcmcia/ray_cs.opts there is a line like this:
"module "ray_cs" opts "...". Here you have to modify some settings
at data-link level present in "opts" .
Arguments:
· pc_debug=x , where x is the log level.
· net_type=x, x=0 for AdHoc, x=1 for Infrastructure.
· essid=x, x is the ESSID
Finally, to verify configuration with pc_debug > 0, you will see data-
link messages in your console like these: "network started" for a new
Wireless network created and "network joined" for a new Wireless
network joined to another one.
Also File /proc/ray_cs can help you: flied BSSID report to which
Subnet you belong to, if it is null you can receive data from no one
cards.
6.4. Lucent Wavelan I, II, Orinoco products and Cabletron
Network type: DSSS, Adhoc and Infrastructure.
Lucent products are very professional ones.
Web site: http://www.lucent.com and http://www.orinoco.net.
Setup is like WebGear-like: step 1,2,3 are similar
Then you have to add to file /etc/pcmcia/config.opts: module
"wavelan_cs" opts " ..." for Lucent Wavelan I module and "wavelan2_cs"
opts " ...", for Lucent Wavelan II or Orinoco.
Under opts you will specify:
1. port_type=x, where x indicates Adhoc(3) or Infrastructure(1)
2. channel=x, x=channel, option relevant for AdHoc mode only.
3. transmit_rate=x, to fix the speed rate: attention to this setting
for compatibility with Cabletron cards.
Note: Ideally, it is possible in a Linux Box to have 2 Lucent Wavelanx
cards, one in Adhoc mode and the other in Infrastructure mode. Only
one of them could properly works because, when starting pcmcia
service, all 2 cards are set with same opts value (so in Adhoc or
Infrastructure mode). So we have to create a Linux module (or maybe a
user mode program) that can change data_link parameters at run-time
such as access mode and channel used in Adhoc mode!
The channel parameter is usually used to avoid interference with near
other Wireless TX/RX.
Lucent drivers could also be used for Cabletron cards
http://www.cabletron.com
6.5. YDI
Network type: DSSS, Adhoc and Infrastructure.
YDI sells very professional cards with antennas, amplifiers and more.
Web-site http://www.ydi.com
To install:
1. untar it in a empty directory.
2. type make for compile.
3. make install to install the driver am930_isa and the wlanctl
utility
Once done you can choose if type manual commands using "wlanctl" data-
link utility or run the "scripts/wlan" file or "scripts/rc.wlan" file
to automatically config your network.
In manual case these are major settings:
1. "wlanctl scan ..." to search for BSSs already present.
2. "wlanctl netlist" show you what's found with "wlanctl scan ...".
3. "wlanctl bsscreate ... ssid" to create a new network with ssid
parameter.
4. "wlanctl bssjoin bssid" to join the network identified by bssid.
5. "wlanctl authen" and "wlanctl assoc" for authentication services.
7. More about Wireless
7.1. A Wireless Linux distribution
The wireless distribution FlyingLinux started in October 1999 in the
Telecommunication Systems Lab at Teleinformatics KTH with the
objective of studying the possibilty of using MobileIPv4 and standard
DHCP-based wireless access for student labs.
The result of that work was the FlyingLinux environment available for
one hundred students and teachers during the 2G1303 project course
that was held from March to May year 2000.
FlyingLinux is the first linux distribution oriented to mobility
services. We have taken care of the security issues including
Kerberos support and OpenSSH.
FlyingLinux is part of the Open Source movement. We have included
software that have been developed at KTH under the GPL licence.
You can find the Wireless Linux distribution at this Web Site
<http://www.flyinglinux.net>.
Mantainer: Alberto Escudero Email <mailto:aep@it.kth.se>, Home Page
<http://www.it.kth.se/~aep>
8. Useful links
8.1. Open software link
· Linux-wlan project <http://www.linux-wlan.org/>
· Jean Tourrilhes Wireless Howto
<http://www.hpl.hp.com/personal/Jean_Tourrilhes/Linux>
8.2. Commercial link
· Fatamorgana Computers <http://www.fatamorgana.com>
· Lucent web site <http://www.lucent.com>
· YDI web site <http://www.ydi.com>
· Siemens web site <http://www.siemens.com>
9. FAQ - Frequently asked questions
Q1: What's the difference between BSSID and ESSID and when I need a
ESSID?
A1: BSSID is 48 bit number used to identify the BSS short area, where
all hosts talk each other (eventually with an Access Point) ESSID is a
variable length string that can let communicate different BSS are to
extend it to a Extended Service Set (ESS). There is one Access Point
for each BSS and all they talk together only if you belong to the same
ESSID. Really you need ESSID if you have a large network with at least
2 Access Points.
Q2: What Access Point I have to buy?
A2: The less expansive you find: what is important is that the Access
Point and the cards you are using use the same Physical Layer
Specific: all FHSS compatible or all DSSS compatible. Attention to
Proxim RangeLan2 cards that cannot talk with other standard FHSS
because they use the proprietary protocol OpenAir.
Q3: What do I use the channel setting for?
A3: When you have more network with different BSS (and with different
vendors) you could have interference problem: changing channel on
Access Points or in Adhoc mode hosts could help you avoiding this kind
of problems.
Q4: Why I cannot set channel on Infrastructure hosts?
A4: Because the channel is decided by the Access Point.
10. Appendix A - Netmask 255.255.255.255, proxy arp and bridging
Here we view some Linux advantages in Wireless Internetworking.
Linux let you specify a netmask like 255.255.255.255 for an interface
which can help you assign IP addresses in to any interface you want,
for example one in eth0, another in eth1 and so on...
This has not particularly side-effects.
In addition you have proxy arp setting under
/proc/sys/net/ipv4/conf/ethx/proxy_arp where ethx if your interface.
If you "echo 1 > proxy_arp" you enable proxy_arp for that interface
while with "echo 0 > proxy_arp" you disable it.
What's proxy_arp? Quickly proxy arp help you when you want a router
answer to an ARP request if the destination address is in another
interface of the linux router.
Example:
192.168.1.1 ---- 192.168.1.2 Linux router 192.168.2.2 ----192.168.2.1
To get this example working you should:
Without proxy-arp
1. In 192.168.1.1 host to set 192.168.1.2 as gateway
2. In 192.168.2.1 host to set 192.168.2.2 as gateway
3. pinging with success from any edge.
With proxy-arp
1. In 192.168.1.1 host to set 192.168.1.2 as gateway
2. do not set gateway for 192.168.2.1 host but enable proxy_arp for
right interface of the router.
3. pinging with success from any edge
Proxy-arp in 2. case let the linux router answer when you ping from
192.168.2.1 host, saying that it has the 192.168.1.1 host so it can
answer for it. After, when the source start sending ICMP packet, Linux
router knows that it have to redirect it to the real host 192.168.1.1
In Wireless network proxy arp can help you if you have many Linux
boxes that acts as IP Forwarders and you wouldn't set to all hosts a
number of static route.
You also can experiment Linux bridging in Wireless network:
1. install a recent stable kernel
2. download good bridge utils at http link or ftp link
Bridging should be more simple to manage.
11. Appendix B - Siemens DECT Radio Modem
Web Site: http://www.siemens.com
What's that? These 2 components are not real PC cards but are more
like modems that you use as external device.
Host1-serial - RadioModem1 - - - - - RadioModem2 - serial-Host2
How can I connect it?
If you see them in an abstract vision you can model them like this:
Host1-serial - - NULL MODEM CABLE - - serial-Host2
So you'd have a connection between 2 far serials with 2 possible
configurations:
1. Linux with Windows, Linux has a daemon that answer to a ppp call
while Windows has a Dial up connection under Remote Access.
2. Linux with Linux, where you can run (on all 2 hosts) a ppp
connection, with IP addresses inverted.
For 1 you can use this simple script in Linux:
"/usr/sbin/pppd -detach lock idle 300 crtscts connect "/usr/sbin/chat
-v TIMEOUT 5 AT OK AT OK AT OK AT OK" IPLINUX:IPWINDOWS /dev/ttySx
115200 disconnect "/usr/sbin/chat -v AT OK" ms-dns IPDNS"
where:
· /dev/ttySx is your serial port,
· IPDNS is the IP address of your dns server,
· IPLINUX is the Linux IP address as IPWINDOWS is the Windows IP
address.
The above script is need for letting Windows believe there is a modem
on the serial end!
In Windows you need to create a Dial Up connection with crtscts
enabled, speed at 115200 and with a stupid number to call (need by
Remote Access but absolutely not used).
With 2 Linux boxes you only have to run a very simple script like this
at each Linux side:
"/usr/sbin/pppd passive local crtscts IPLINUX1:IPLINUX2 /dev/ttySx
115200 noauth persist"
where you'll invert IPLINUX1 with IPLINUX2 at the other edge.
Note that you can do authentication even Linux-Windows than in Linux-
Linux if you want.
