My laptop has connected to my wireless router (a Cisco one)however, when I try iwconfig, I get weird result:
Lenovo-G570:~$ iwconfig
lo no wireless extensions.

eth0 no wireless extensions.

eth1 IEEE 802.11 Access Point: Not-Associated
Link Quality:5 Signal level:215 Noise level:159
Rx invalid nwid:0 invalid crypt:0 invalid misc:0

Lenovo-G570:~$ iwlist eth1 scan
eth1 Interface doesn't support scanning.

However, I can access internet through my wireless router. Does anyone can explain this? I build the linux kernel by myself and it is:
Lenovo-G570:~$ uname -a
Linux Lenovo-G570 3.0.32 #1 SMP Fri Jun 1 10:26:17 PDT 2012 i686 i686 i386 GNU/Linux


Thanks!
moonleo

Sorry to ask this, but can you try

xin@xin-Lenovo-G570:~$ ifconfig -a
eth0 Link encap:Ethernet HWaddr b8:70:f4:2b:09:ab
UP BROADCAST MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
Interrupt:43

eth1 Link encap:Ethernet HWaddr cc:af:78:25:4c:95
inet addr:192.168.1.141 Bcast:192.168.1.255 Mask:255.255.255.0
inet6 addr: fe80::ceaf:78ff:fe25:4c95/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:19367 errors:1 dropped:0 overruns:0 frame:3009353
TX packets:5821 errors:16 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:16036497 (16.0 MB) TX bytes:483739 (483.7 KB)
Interrupt:17

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:25 errors:0 dropped:0 overruns:0 frame:0
TX packets:25 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:1572 (1.5 KB) TX bytes:1572 (1.5 KB)

Still no wireless interface although I know eth1 connect to wireless router

eth1 is the only configured interface, so this might really be the one connected to the router. I could see some RX/TX errors on the interface, so this might be the reason why iwconfig says the interface is not associated with an access point, although the configuration was setup and the network is working. Not so sure though.

If it is not associated, how can the network work?

xin@xin-Lenovo-G570:~$ ping google.com
PING google.com (74.125.224.70) 56(84) bytes of data.
64 bytes from nuq04s07-in-f6.1e100.net (74.125.224.70): icmp_req=1 ttl=55 time=19.6 ms
64 bytes from nuq04s07-in-f6.1e100.net (74.125.224.70): icmp_req=2 ttl=55 time=19.4 ms
64 bytes from nuq04s07-in-f6.1e100.net (74.125.224.70): icmp_req=3 ttl=55 time=20.5 ms
64 bytes from nuq04s07-in-f6.1e100.net (74.125.224.70): icmp_req=4 ttl=55 time=20.2 ms

That is why I say iwconfig give wrong result ....

What I mean is, the association process between the AP and the interface returned errors, although the IP configuration process pushed through. I'm not sure why this happened though. I suggest you try reading log files why that happened,

If there is error and association fail, AP will not allow STA　pass any traffic through it
Then how can STA ping google?

I agree. Association should come in first, where parameters are being exchanged, such as windows size and authentication, then IP configuration are negotiated. This is why I suggest you read the log files to investigate, or enable logging then reconnect.