I tried troubleshooting this on the Ubuntu forums, but my thread went nowhere, so here I am! I'm REALLY hoping someone can help, because this is immensely frustrating.

I just moved to a new house, with a new ISP. All of a sudden, all the machines running Ubuntu (there are 4 of them on my network) are having trouble rendering websites properly. Some websites are perfectly fine; some render with things missing (e.g., no photos or no CSS); some render as text-only; and some won't display at all - I get a "server not found" error.

If I boot into Windows on any of these machines, there's no problem.

To complicate matters more: Sometimes the "server not found" sites will decide to connect, then they'll fail again. This has been changing day to day (sometimes even hour to hour). Anything within the google.com domain is a good example of this.

Two of the affected machines are desktops (one running headless as a server), and two are laptops. All four are running Ubuntu, but they're all running different kernels. The ONLY things these machines have in common is that they're running Ubuntu, and they're all connecting to the internet wirelessly.

Because things work properly in Windows without exception, and because (at least on the laptops) things work fine in Ubuntu on any other internet connection, I can rule out wireless network adapters. I have tried using two different wireless routers - no change. I have tried using 4 different web browsers - no change. I have tried plugging a laptop directly into the incoming connection, bypassing the router entirely - no change. I have tried purging and reinstalling Flash on one of the laptops - no change. I have tried to connect to affected websites using their IP addresses to rule out DNS issues - no change.

This one has me completely stumped. The only thing I can think is that this is something to do with my ISP, but I can't imagine what it would be. I called the guy who runs the ISP (it's a local outfit run by one or two guys, as I'm living in the middle of nowhere), and he said there's nothing he's aware of at the ISP level that would be causing a problem like this.

Any help you can offer will be very much appreciated. I'm getting sick and tired of booting into Windows. I want my Linux back!!

Thank you!

Can you look at /etc/resolv.conf? what does it say? Are there lines that say 'nameserver'?
Do those match the DNS nameserver of your new ISP?

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Obvious check: compare the output of aboutlugins in both browsers, but I'm sure you're up with that.
These problems get solved when you find a site that regularly misbehaves in a particular way. If you're in the backside of nowhere, lag or bandwidth could be issues. DNS may also be at issue; for instance, a web page may have a youtube link in there, but if linux can't resolve www.youtube.com quickly, then you don't get to see it. Try using opendns.org or some such. If that fails, you can try a small dns server yourself, dnscache sounds ideal if you'll let the stuff near a box in your net.
http://www.cr.yp.to

I'd agree with Alan99 there - check the nameservers that Ubuntu is trying to use.

It's also worth checking that the browser you are using on Ubuntu is not set up to use some kind of proxy / privacy service that is no longer relevant - Firefox would have these under EDIT > PREFERENCES > ADVANCED > NETWORK TAB > SETTINGS BUTTON

And that you don't have any odd firewall rules (Firestarter/Iptables) relating to the old IP ranges of your previous ISP.

Here are the contents of my /etc/resolv.conf:
This is new territory for me, but I'm thinking those contents aren't what they should be...

EDIT: The above is from the /etc/resolv.conf file on my own laptop. I just confirmed that the contents of the /etc/resolv.conf file on my server are exactly the same. Also, I have no idea how to find out what the DNS nameserver of my ISP is.

OK. Is the device at '192.168.100.1' a nameserver, dhcp server or xDSL router?
I would want to know this device does with DNS queries.

Out of curiosity -
Is the Ubuntu machine getting an IP address via DHCP or static?
Does the Windows machine get an IP address via DHCP or static?

That's just it - there is no device at 192.168.100.1!

That got me thinking. Perhaps it's trying to point to my router, which is located at 192.168.1.1. I made the change in my resolv.conf file, and it seems like my issue has been completely solved!

Just to make sure I have everything straight, though: The device at 192.168.1.1 is a Linksys WRT160N router. It distributes all IPs via DHCP, regardless of OS.

You could try:
disable ipv6
verify or disable firewall
use open dns
remove
Verify the default gw
What is the output from

If there is no device at 192.168.100.1 check your network manager applet - as it has owned up to writing /etc/resolv.conf you can bet it's putting that in place 'helpfully' for you :-) Probably from something in the past.

If I right-click on the NM icon on the panel, and then click Connection Information, sure enough, the following line shows up:

I can't figure out how to change that to the proper address. This is important, because every time I boot up and NM connects, it's going to rewrite my resolv.conf file. I know this because it just did it to me!

Other than that, THANK YOU for your help on this!! I've been fighting this for weeks now, and it feels good to finally have it resolved.

Network Manager is my Nemesis arggggg! I've removed it myself so I can't tell you how to edit it. I seem to recall I could only change some settings as root {or the first installed user on the box} with nm-applet but I don't recall how. Perhaps someone with NM knowledge can advise?

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@doctorbighands: If you're on dhcp, then there's network scripts to start. If the setting "DHCPKEEPRESOLV" in your config is true or yes, then your resolv.conf is not overwritten each time you start.

Try setting the dns servers in your router (If you can) and that should get around it. Otherwise, you'll need DHCPKEEPRESOLV="yes" somewhere in /etc/sysconfig.

resolv.conf should not be edited by hand, as normally entries are placed in it by the name resolving service (libnss I believe) If you are pointing to your router correctly (if there is an incorrect entry gateway=192.168.100.1 in your /etc/network/interfaces file it will point to the wrong place) I think that if you are using dhcp on your router it should obtain the DNS entries from the ISP by itself if your machines can get the entries from your router. I myself don't use network manager to setup my connection as I have a laptop, so use wifi-radar and have a net-applet in my gnome-panel to select connections.

I'm in Ubuntu, so I don't have an /etc/sysconfig, and I'm not sure where else to look for a DHCPKEEPRESOLV. Hmm...

Also, in my router settings, there are two entries of note, both under the Status tab. One is "Default Gateway," and the other is "DNS1". They both read as 192.168.100.1. The problem is, I can't figure out how to change them! I'm pretty sure that this is where Network Manager is getting that address, so if I can figure out how to change those entries in my router, I'm probably good to go. I tried restoring my router to factory settings, and that still didn't do the trick.

I've restored my web access by editing my resolv.conf at every boot. I hate to have to keep doing that.

If anyone has any ideas about how I can get this resolved fully and permanently, I'm all ears. Thanks!

try this
cd /etc
grep -r DHCPKEEPRESOLV *

It's a common variable in the init scripts, but is usually set externally.