Kiran Divekar has over 15 years of experience in the IT industry working for major companies in wireless technologies. He is currently vice-president of GeeP and was a major contributor to the Marvell wifi driver in the Linux kernel. The document goes on to define key wireless networking terms and concepts, describe the basic components and configuration of wireless networks and devices in Linux, and discuss tools and internals for debugging and development.

1. Kiran Divekar
kirandivekar@gmail.com
Wireless:
Basics to Internals

2. About...
 15 years of IT industry experience
 Worked in multinationals like PMC Sierra,
Persistent, Nevis Networks, Marvell
Semiconductors, Ericsson.
 Vice-president of GeeP
 One of major contributors of Marvell wifi driver
in Linux Kernel tree. (mwifiex)

3. WiFi Devices
Wireless Sniffer
UUT
Cisco AP (bg)
Marvell AP (bgn)
STA for Adhoc

4. Wireless Network Connection

5. Wireless Network Connection

6. Wireless Network Connection
 Linux Kernel :
 CONFIG_NET_RADIO, CONFIG_CFG80211
 Wireless Access Point :
 Device for network connection
 Supplicant :
 Program to connect to AP
 GUI :
 Network Manager

7. Wireless Networks
 Infrastructure :
A − − − | − Access Point − − Access Point − | − − − D
B − − − | BSS1 BSS2 | − − − E
 Ad-hoc :
A − − − − − C
/
| / |
/
| / |
/
B − − − − − D

8. Infrastructure vs. Adhoc Networks
infrastructure
network
ad-hoc network
AP
AP
AP
wired network
AP: Access Point
Source: Schiller

9. Wireless Terms (802.11)
Access Point :
 A wireless access point (WAP) is a device that
acts as the central hub of all wireless data
communications.
Service Set ID :
 SSID is used to identify a network in wireless
domain.
Basic Service Set ID :
 MAC address of the WAP used to identify part of
network in a SSID.
Mode :
 Infrastructure (Managed) or Ad-hoc mode.
Channel :
 One of Predefined channels from 1 to 16 in terms
frequency range of 2.4 GHz to 2.5 GHz.

10. Wireless Terms (802.11)
Encryption :
 Method of encoding or scrambling data so that
only people with the secret key to unlock the code
can view the original data.
WEP: Wired Equivalent Privacy
WPA: WiFi Protected Access.
RSN(WPA2) : Robust Security Network.
WPSK : Pre-Shared Key.
EAP : Extended Authentication Protocol

11. Network configuration
 # Intel Corporation PRO/Wireless 3945ABG
Network Connection
DEVICE=wlan0 (check udev)
ONBOOT=yes
BOOTPROTO=static
HWADDR=00:19:d2:59:15:d2
NETMASK=255.255.255.0
IPADDR=192.168.1.100
DOMAIN=
TYPE=Wireless
ESSID=linksys
CHANNEL=6
MODE=Managed
RATE=

12. Wireless (GUI)

13. Connecting to Network
 Scan available networks
 iwlist wlan0 scan OR iw dev wlan0 scan
wlan0 Scan completed :
Cell 01 - Address: 00:18:39:2F:AD:86
ESSID:"linksys"
Mode:Master
Channel:6
Frequency:2.437 GHz (Channel 6)
Encryption key:on
IE: IEEE 802.11i/WPA2 Version 1
Group Cipher : CCMP
Pairwise Ciphers (1) : CCMP
Authentication Suites (1) : PSK
Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 11 Mb/s; 6 Mb/s
9 Mb/s; 12 Mb/s; 18 Mb/s; 24 Mb/s; 36 Mb/s
48 Mb/s; 54 Mb/s

14. Connecting to Network
 Associate a particular network (SSID)
 iwconfig wlan0 essid “linksys” OR
iw dev wlan0 connect “linksys”
 iwconfig wlan0
wlan0 IEEE 802.11g ESSID:"linksys"
Mode:Managed Frequency:2.437 GHz Access Point:
00:18:39:2F:AD:86
Bit Rate=54 Mb/s Tx-Power=27 dBm
Retry min limit:7 RTS thr:off Fragment thr=2346 B
Encryption key:C589-F156-8324-1564-021A-4EF6-5D52-6818 [2]
Link Quality=83/100 Signal level=-51 dBm Noise level=-55 dBm
Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0
Tx excessive retries:0 Invalid misc:0 Missed beacon:0

15. Wireless (GUI)

16. Connecting to Network
 iwlist wlan0 scan
 iwconfig wlan0 essid “linksys”
 Authenticate to one of APs (BSSID)
in that network.
 4 –way handshake for PSK
 WEP key exchange
 Dot1x handshake for EAP
 Check network connectivity
 ping <Ip address of AP>

17. Wireless Applications
 NetworkManager : Dan Williams
www.gnome.org/projects/networkmanager/
 Wpa_supplicant : Jouni Malinen
http://hostap.epitest.fi/wpa_supplicant/
 Hostapd
http://hostap.epitest.fi/
 KwifiManager
http://kwifimanager.sf.net
 Intel cards [ iwl3945, iwlwifi]
http://www.intellinuxwireless.org

18. Common Pitfalls

19. Wifi device


Where is my wifi device?
I can't do anything without that :-)
=>lspci or lsusb or similar.

ifconfig : see all network interfaces including wireless.

Driver for wifi device

Part of Linux Kernel Tree

Vendor Supplied Custom Driver.

Re-compilation needed?
=> Get kernel source
=> Recompile driver. (make ?)
=> Load driver (insmod)

20. Wifi device

21. rfkill

Used to enable / disable wireless, BT devices
=> Hard Blocked.... check hardware switch
=> Soft Blocked....

rfkill unblock wifi

22. ifconfig

Check ifconfig wlan0
wlan0 Link encap:Ethernet HWaddr e0:06:e6:d8:5e:9d
inet6 addr: fe80::e206:e6ff:fed8:5e9d/64 Scope:Link
UP BROADCAST MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:609842
TX packets:83 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:0 (0.0 B) TX bytes:14499 (14.4 KB)
Interrupt:19

If not up,
=> ifconfig wlan0 up

Network Manager Conflicts:-
=> service network-manager stop


23. Wifi HotSpot

Requires AP-STAwifi device capability
=> What is AP-STA???

Check Your Android Phones.
=> Android AP.

Wifi Direct:-
=> PlayStations, TVs, Printers

Features:-

=> simultanous operations on same channel.

24. WiFi Hotspot (GUI)

25. Wireless Debugging
Sniffer: www.wireshark.org

26. Wireless Internals
Iw dev wlan0 connect “linksys”
MAGIC ?

27. Wireless Tools
The Wireless Tools (WT) is a set of tools allowing
to manipulate the Wireless Extensions. They use a
textual interface and are rather crude, but aim to
support the full Wireless Extension. There are
many other tools you can use with Wireless
Extensions, however Wireless Tools is the
reference implementation.
 iwconfig manipulate the basic wireless parameters
 iwlist allow to initiate scanning and list
frequencies, bit-rates, encryption keys...
 iwspy allow to get per node link quality
 Iwevent to read the wireless events
 iwpriv allow to manipulate the Wireless
Extensions specific to a driver (private)

28. System call trace

29. Driver Firmware interface
What is a firmware ?
• Firmware is wireless networking software that
runs on the wireless chipset.
• The wireless device driver downloads the
firmware to the wireless chipset, upon
initialization.
• All low level wireless operations (Tx, Rx) are
performed by the firmware software.
• It works in two modes
 Synchronous Request, response protocol
 Asynchronous Events from FW.
• The firmware resides in /lib/firmware/
e.g. /lib/firmware/iwl-3945.ucode

30. User space Control
=> Basic tools like iw, iwconfig, iwlist
=> wpa_supplicant or NetworkManager
=> ConnManager

31. mac80211
=> Mac80211 is Linux kernel subsytem
=> Implements shared code for soft MAC, half MAC
devices
=> Contains MLME
• Beacon
• Probe Request, Response
• Associate
• Autenticate
• De-associate
• De-authenticate

32. cfg80211
=> Linux kernel layer between user space and mac80211
=> Sanity checking, protocol translations

=> Much thicker than WEXT.

=> CRDA. (Regulatory Domain)

33. Kernel configuration

34. Architecture

35. More
=> Internals of cfg80211, mac80211
=> CRDA : US, EU, JP
=> Configuration, data transmission, reception
=> http://wireless.linux.org
=> linux-wireless@vger.kernel.org

36. Wireless Basics & Internals
Thank You