Hello Greg & Ed,
Thank you for response quickly !
Greg,
you point out the things I forgot to check. There is a built-in
Ethernet Adapter, fxp0, in my laptop. I use it to complete NetBSD's
install process. It was assigned a default gateway, 192.168.1.1, and has
a start script as ifconfig.fxp0 in /etc. However, my access point's IP
is also 192.168.1.1. For avoiding confuse, I delete /etc/ifconfig.fxp0
and comment default gateway in /etc/rc.conf. Then reboot my laptop
again. Great ! I can surf Internet via my usb wifi adapter.
Ed,
you give me a new thought about saving USB port for something else. My
laptop has PCMCIA device. But it had never been used. Although it is ten
years old, I don't want to lose it. This is my first laptop. I use it
to learn Linux and take some projects as freelancer. Actually, I want to
do something with it. But I have no idea now.