Question: I run ubuntu 10.04 and I installed a wlan like:

[modem]---ethernet cable--[wireless router]----ethernet cable--[my PC]

Computers using the wireless network can access all pages normally.

I, on the other hand, using ethernet, am limited:

1. I cant login on facebook (it enters facebook.com if I'm not logged in, but once
I log in everything stops working)
2. I can't post (but can browse) on stackoverflow and similar
3. I can't post (but can browse) on ubuntuforums.org

When I skip the wireless router and do:

[modem]----ethernet cable--[my PC]

I can access everything normally.

I inspected the wireless router page but everything seems normal to me (but I'm not an 'expert')

Some help please. I can post output of any command here.

**UPDATE 1:**
I found out that I cant upload images too while connected to the router.

DHCP config for modem
![enter image description here](https://i.stack.imgur.com/LJwB0.png)

Router  

![enter image description here](https://i.stack.imgur.com/q6YmX.png)

Answer: 
The key to this issue and the answer to your questions came from [your comment](https://superuser.com/questions/686738/home-wlan-wont-let-me-do-very-specific-thingslog-in-facebook-post-on-some-for#comment963759_686738) which indicated that you put the modem in bridge mode.

What was happening was that your modem had a built-in router (along with firewall functionality and possibly other things like QoS, etc.) Connecting directly to the modem-router worked as expected, but when you connected through another router which then connected through the modem’s router, things got messed up. The issues is that connecting multiple routers like that makes a right mess of [NAT](https://en.wikipedia.org/wiki/NAT). Depending on the various configurations of the two routers (DHCP, QoS, firewall settings, etc.), and on how many systems you are connecting to it (e.g., any laptops connecting wireless) it may or may not work sometimes and/or all the time.

As you discovered, switching the modem into bridge-mode (turning off the router capabilities and using it as a only a modem) solved the problem because now you are using only your D-Link for a router.

(If you really want to try to use both, you could try turning off the DHCP servers and using static IPs on both from the **LAN side**, but it’s probably more trouble than it’s worth, especially since you won’t really be getting significantly more benefit from being behind two firewall-routers.)

(I went through this same scenario last year when I tested every permutation of using my trusty DI-524 along with Rogers’ crappy Hitron. I eventually gave up and switched it into bridge-mode for a while, but then returned the pile of junk the next month and got back the DOCSIS 2.0 modem-only Surfboard I had before—which was half of the monthly rental price of the useless Hitron.)
Try changing the Primary and Secondary DNS Server in the DHCP settings as below

Primary DNS Server : 8.8.8.8
Secondary DNS Server : 8.8.4.4

Bascially the above DNS servers are provided by Google for IPv4. For IPv6 use these

Primary DNS Server : 2001:4860:4860::8888
Secondary DNS Server : 2001:4860:4860::8844

Maybe this will help You