My net card is enthernet net card.I lived in Nanjing University of Posts and Telecommunications,China.I can directly link to any nodes which provide service in my school.But if I want to link to the Internet,I must buy a username and password,use pppoe way to link to the Internet.My ISP is "Jiangsu telecommunication".
When I set a ppp0 interface in the net interface set up,the install exit by forced.Installed again without adding the ppp0 interface,install got success.After that,I downloaded two source code package: ppp and rp-pppoe,unpacked and installed.Then I used pppoe-setup to set the username,password,interface(eth0),firewall(1),DNS( my ISP provide DNS and dhcp ip,so I directly type enter,second time I set DNS and secondary DNS by hand,but the same thing came),then typed pppoe-start to link to the Internet(if I set wrong username or password,it showed ......can not connected.if right,it showed ...connected!).After connected!,I can not use firefox or gftp or gaim to link to the Internet(all setting are right).I got the www.google.com and ftp.freebsd.org 's IP from my roommate's computer(they use windows xp),still can not link without using DNS.I need help because it is a big problem.
May be there are some problems.As you said:
The follows are what showed when I typed ifconfig -a after connected:

eth0 Link encap:Ethernet HWaddr 00:13:8F:C1:48:94
inet addr:10.200.11.249 Bcast:10.200.15.255 Mask:255.255.248.0
UP BROADCAST NOTRAILERS RUNNING MULTICAST MTU:1500 Metric:1
RX packets:38276 errors:0 dropped:0 overruns:0 frame:0
TX packets:33791 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:48462889 (46.2 MiB) TX bytes:4032736 (3.8 MiB)
Interrupt:16 Base address:0x6000

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:8 errors:0 dropped:0 overruns:0 frame:0
TX packets:8 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:560 (560.0 b) TX bytes:560 (560.0 b)

ppp0 Link encap:Point-to-Point Protocol
inet addr:221.226.45.194 P-t-P:221.226.45.129 Mask:255.255.255.255
UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1492 Metric:1
RX packets:16 errors:0 dropped:0 overruns:0 frame:0
TX packets:4 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:3
RX bytes:764 (764.0 b) TX bytes:37 (37.0 b)

and in /etc/resolv.conf there is the right DNS
# Generated by dhcpcd for interface eth0
nameserver 202.119.230.8
nameserver 218.2.135.1