I have a laptop, the wifi is OK, but for wired network, if I'm using windows, it is OK. But with linux, yesterday, it is OK, but today I can't access the network through eth0(in windows, it is OK), what are potential problems?

BTW, yesterday I modified MTU from 1406 to 500, but then modified it back to 1406.

eth0 Link encap:Ethernet HWaddr 5C:26:0A:2B:B8:06
inet addr:138.96.201.72 Bcast:138.96.207.255 Mask:255.255.240.0
inet6 addr: fe80::5e26:aff:fe2b:b806/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1406 Metric:1
RX packets:21221 errors:0 dropped:0 overruns:0 frame:0
TX packets:1355 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:3710568 (3.5 MiB) TX bytes:130299 (127.2 KiB)
Interrupt:20 Memory:f5400000-f5420000

additional information: 1 it seems it is from dhcp coz I didn't do any configuration for the ip address, and it is a public IP. but the ip is fixed

2 I think the /etc/resolv.conf is fine, coz previously the network is fine

You have not provided a lot of information.

What distro are you using?

Are you using software like Network Manager or WICD to configure and control your adapters?

Where is this DHCP server? Is it in a router at your location?

Please describe the network connection. If it is a router/modem provide the make and model.

Is this address in the same network as your other adapters when they are working?

When you said how did you do the testing? A web browser only? Did you try pinging your modem/router? Points outside like yahoo?

Why is your MTU 1406? The default is 1500.

fedora 16

I don't know, how to check this?

how to check this?

it is in a institute

no
but when I'm using windows, the network is OK

I used ping, web browser

I did some googling, it appears Fedora 16 comes with Network Manager. You should have an icon somewhere on your desktop for NM. You can configure your interfaces, activate them and deactivate them with NM. This is the first place to look when you have problems communicating with the outside world.

You are in an institution. The IP address I see may, or may not be correct to get to the outside world. You will need to find out from the network admins what IP addresses you can use. You may be connecting to an internal network, with out outside access. I have no way of knowing what addresses will work.

One thing you can do, is run the command netstat -r in a terminal. I would like to see if you have a gateway address set. This is what the output looks like.

Under the heading Gateway, you see an entry 'cisco'. This is my router. It is also my gateway. gateways are the path to the outside world. You probably will have a doted decimal IP address here, or nothing. I have a name, since I updated the /etc/hosts file with a name for the router. ( not necessary for it to work).

In order to use ping to the outside world, you need to know various IP addresses. It helps a lot if you also know the IP addresses of key spots in your network. You should find out the IP's of the Gateway, and one or two other systems on the internal network.

Resolv.conf gets overwritten. You should check it, to see if the IP's in there are valid for your location. Once again, I can not tell you what should be there. Network admins, or, since windoze works, and your wireless works, connect there, and look at what you get. Your IP, whats in resolv.conf, gateway.... Then look at the problem on eth0 when failing.

I notice that, after rebooting, eth0 doesn't work
but if I deactivate the eth0 and then activate it
it works

what is wrong with this?

Most likely it has to do with the configuration setup you have. I asked earlier if you were using Network Manager, or WICD. As far as I can tell, ( I don't run Fedora ) it uses Network Manager by default.

Look to see if you have an icon somewhere, that looks like a terminal, or modem. If you see it, hover the mouse pointer over it. If it displays some info, click it. Look in there for what configuration you have. Some are set up to activate wireless first. If you deactivate wireless, then some will try the wired connection. See what you can find.