wpa_supplicant.: Simulating handoff between wifi's access points.

[Dan Williams]

On Tue, 2012-12-18 at 17:03 -0300, Carlos Patricio Amigo Haering wrote:
> Hi everybody,
> 
> I'm working on a seamless handover but i don't want to walk long 
> distances with the client to trigger the handover so i need to simulate 
> it. Basically i have two AP with the same SSID and different MAC and i 
> want to disconnect a client from one of them to connect it to the other 
> one.  First i tried with iwconfig(iwconfig wlan0 ap <mac>)  but this did 
> not do nothing, apparently this tool it's deprecated.
> 
> Reading and asking, somebody told me about wpa_supplicant and i've been 
> looking for some good tutorial but all of them are a little bit simple 
> and normally uses dhcp and my AP doesn't have dhcp server. Anyway i've 
> made something using a mix of info of internet but without good results, 
> indeed i can't connect the client to a AP yet. I hope that you help me 
> to figure out what i'm doing wrong.
> 
> I'm using Ubuntu 10.10 with kernel 2.6.35-22-generic and a network 
> controller: Intel Corporation PRO/Wireless 4945ABG.
> 
> # ifconfig wlan0 down
> # ifconfig wlan0 up
> # iw wlan0 scan
> BSS 20:aa:4b:48:7e:ca (on wlan0)
> 	TSF: 3914550832 usec (0d, 01:05:14)
> 	freq: 2462
> 	beacon interval: 100
> 	capability: ESS Privacy ShortSlotTime (0x0411)
> 	signal: -15.00 dBm
> 	last seen: 1500 ms ago
> 	SSID: OF
> 	Supported rates: 1.0* 2.0* 5.5* 11.0* 6.0 9.0 12.0 18.0
> 	DS Parameter set: channel 11
> 	ERP: Barker_Preamble_Mode
> 	Extended supported rates: 24.0 36.0 48.0 54.0
> 	RSN:	 * Version: 1
> 		 * Group cipher: CCMP
> 		 * Pairwise ciphers: CCMP
> 		 * Authentication suites: PSK
> 		 * Capabilities: 16-PTKSA-RC (0x000c)
> 	WMM:	 * Parameter version 1
> 		 * BE: CW 15-1023, AIFSN 3
> 		 * BK: CW 15-1023, AIFSN 7
> 		 * VI: CW 7-15, AIFSN 2, TXOP 3008 usec
> 		 * VO: CW 3-7, AIFSN 2, TXOP 1504 usec
> 
> # wpa_supplicant -v
> wpa_supplicant v0.6.10
> Copyright (c) 2003-2009, Jouni Malinen <j at w1.fi> and contributors.
> 
> # cat /etc/wpa_supplicant/wpa_supplicant.conf
> ctrl_interface=/var/run/wpa_supplicant
> 
> network={
> 	ssid="OF"
> 	bssid=20:aa:4b:48:7e:ca
> 	key_mgmt=WPA-PSK
> 	group=CCMP TKIP
> 	pairwise=CCMP TKIP
> 	proto=RSN
> 	psk=4825dfb64863f17ff2db453445a123191468752148d88ffe4491bc79cae5f95f
> 	id_str="my_static_lan"
> }
> 
> Note: The psk= was the output of wpa_passphrase <ssid> <password>.

Note that you can just put the passphrase here, in quotes:

psk="my wifi network passphrase"

and the supplicant will do the right thing.

> # cat /etc/network/interfaces
> auto lo
> iface lo inet loopback
> 
> wpa-driver wext
> wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf

With Ubuntu 10.10, you may want to continue using wext.  However, if you
ever upgrade to newer versions, you'll most definitely want to use the
"nl80211" supplicant driver instead.  wext, like iwconfig, is deprecated
and you'll get better results from nl80211.  These are just the kernel
API for wifi control that the supplicant uses to tell the wifi device
what to do, and nl80211 is more flexible and better featured.  It also
typically works better for roaming between access points.

> iface my_static_lan inet static
> 	address 192.168.1.11
> 	netmask 255.255.255.0
> 	network 192.168.1.0
> 	broadcast 192.168.1.255
> 
> # wpa_supplicant -B -Dwext -i wlan0 -c 
> /etc/wpa_supplicant/wpa_supplicant.conf

As above, if you ever update to after 10.10, you'll want "-Dnl80211"
instead.

> # ip addr show wlan0
> 3: wlan0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq state 
> DOWN qlen 1000
>      link/ether 00:1b:77:15:7d:d1 brd ff:ff:ff:ff:ff:ff
>      inet6 fe80::21b:77ff:fe15:7dd1/64 scope link
>         valid_lft forever preferred_lft forever

The supplicant only handles the wifi bits.  Something else handles the
actual IP addressing.  So if you just run wpa_supplicant, the supplicant
will connect to the wifi and you'll have no IP address.  You then need
to kick off whatever tool gets the IP address.  Not specifically sure
how that's supposed to work on Ubuntu, but it could be just "ifup
my_static_lan" or something like that.

Next if you're about to simulate roaming, look at the wpa_cli tool.  You
want the "roam" command which lets you tell the supplicant to roam to an
access point of your choosing.

Dan

> (Doesn't seem connected.)
> 
> # ping 192.168.1.13 (pinging a iphone connected to the same AP)
> connect: Network is unreachable
> 
> 
> As you see i don't have any error but the client is not associated to 
> the AP. I really appreciate a little help.
> 
> thanks in advance.
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