I'm new to CentOS, but have been using Ubuntu for about a year as my desktop os. I've previously had Ubuntu 9.04 and 9.10 and Windows Vista and XP fully functional on this hardware.

After installing CentOS 5.4, I was able to update and install new software, but I am not able to visit most websites (google, gmail, ask.com, etc.) I can though visit CentOS and several other FOSS type sites such as www.tldp.org.

I've done some searching but I haven't found anything quite like this. I've tried disabling SELinux, and setting it permissive. I've also tried with the firewall enabled and disabled. All to the same effect.

The pc is connected directly to a cable modem and my current installation consists of CentOS 5.4 and Windows Vista Home Premium dual booting.

I would be glad to post more details if they would shed any light.

Thanks for any assistance.

Check your /etc/resolv.conf

Contents of resolve.conf:


cat /etc/resolv.conf
; generated by /sbin/dhclient-script
search domain.actdsltmp
nameserver 192.168.0.1
nameserver 205.171.3.65


This matches the data found on the DNS tab under Network Configuration. Can you tell me if this needs to change?

Thanks for your response.

The "search" looks a bit strange, but that should only have an effect on local host names that are not fully qualified. No way to know about the 2nd nameserver entry - it depends on your ISP. The first looks like your router with a caching nameserver.

Please clarify what you mean by "not able to visit". What error[s] are you seeing?

Either I'm able to access the site normally, as I am currently browsing the CentOS forums. Else, I receive the following error:



Failed to Connect



Firefox can't establish a connection to the server at www.google.com.



Though the site seems valid, the browser was unable to establish a connection.

* Could the site be temporarily unavailable? Try again later.
* Are you unable to browse other sites? Check the computer's network connection.
* Is your computer or network protected by a firewall or proxy? Incorrect settings can interfere with Web browsing.

Sounds like firewall or proxy issues.

Can you ping the offending sites?

It seems I can. I am able to browse CentOS.org (I'm posting this from the pc I'm having trouble with) but I'm not able to browse www.google.com.

ping www.centos.org
PING www.centos.org (72.232.194.162) 56(84) bytes of data.
64 bytes from www.centos.org (72.232.194.162): icmp_seq=1 ttl=54 time=52.7 ms
64 bytes from www.centos.org (72.232.194.162): icmp_seq=2 ttl=54 time=52.9 ms
64 bytes from www.centos.org (72.232.194.162): icmp_seq=3 ttl=54 time=52.9 ms
64 bytes from www.centos.org (72.232.194.162): icmp_seq=4 ttl=54 time=52.8 ms
64 bytes from www.centos.org (72.232.194.162): icmp_seq=5 ttl=54 time=55.8 ms

--- www.centos.org ping statistics ---
5 packets transmitted, 5 received, 0% packet loss, time 4001ms
rtt min/avg/max/mdev = 52.741/53.449/55.836/1.195 ms

ping www.google.com
PING www.l.google.com (74.125.47.105) 56(84) bytes of data.
64 bytes from www.google.com (74.125.47.105): icmp_seq=1 ttl=55 time=74.8 ms
64 bytes from www.google.com (74.125.47.105): icmp_seq=2 ttl=55 time=75.2 ms
64 bytes from www.google.com (74.125.47.105): icmp_seq=3 ttl=55 time=75.0 ms
64 bytes from www.google.com (74.125.47.105): icmp_seq=4 ttl=55 time=75.1 ms
64 bytes from www.google.com (74.125.47.105): icmp_seq=5 ttl=55 time=75.1 ms

--- www.l.google.com ping statistics ---
5 packets transmitted, 5 received, 0% packet loss, time 3999ms
rtt min/avg/max/mdev = 74.882/75.079/75.217/0.209 ms

Is there a proxy server or external firewall between you and the internet?

I'm connected to the internet using a dsl modem from qwest. No additional firewall or router and I didn't setup any proxy servers, I've pretty much left the default install alone. I'm getting the same result whether SELinux is permissive or disabled and firewall is enabled or disabled.

I'm pretty much stumped. Did everything work before updating? Were there any problems with the updates? Did you install anything from 3rd party repos?

Let's see.

I haven't enabled any third party repos. I installed a few things using the package manager and yum. The groupinstall of Ruby and a few random things from the development section. Really, just proving to myself that I was getting outside to access the internet in some way. (I hadn't tried pulling up the CentOS web site yet at that point, because I assumed it was all web sites that I couldn't access.)I installed ntfs-3g by downloading the source and going through the ./configure, make, make install process so I could access an ntfs partition I have.

But this problem has been the same since I initially installed CentOS. I've tried fooling around with the network and proxy settings in firefox, thinking that might be the problem. All to no effect and I returned them to their original settings. Also, I get the same results using the text browser lynx as I'm getting with Firefox, so it doesn't appear to be limited to just Firefox anyway.

I know my hardware is working because I'm fully able to browse the web when I boot under Windows Vista Home Premium AND my hardware hasn't changed since I briefly had CentOS 5.3 installed a few months back. And I didn't have these problems under 5.3.

When I ran out of things to try on my own, I was hoping that there was some obscure security feature that was causing this as the only sites I seem able to connect to seem to consist of FOSS related material.

It seems a little silly, but I'm beginning to consider blowing away 5.4 and re-installing 5.3.

Quote:

Yes, as after an update you will (theoretically) be right back where you are now: 5.3 + updates == 5.4. If you're going to blow away 5.4 anyway, I'd try a fresh 5.4 install and then test before messing with anything else. I have done a lot of 5.4 installs and updates without encountering the problems you're seeing, nor have I seen reports of similar issues in the fora or mailing lists.

I actually tried both approaches. I re-installed 5.3 and discovered I have the same problem. (I can still run package updater and visit a few web pages like these forums, but not most pages, like google.) So I blew that away and re-installed 5.4. I've done nothing at all to this installation except load firefox to make this post and attempt to access google again, but I still have the same problem.

I'm dumb-founded.

Quote:
Hmm... "except load firefox"? Didn't you get Firefox as part of the default install. There's got to be a common thread here. Are you doing other than the standard install?

Quote:
Same here, and I don't like it.

There must be a reason.

At install, I selected three of the main "packages", Desktop-Gnome, Server and Gui-Server. Previously I had only selected desktop. I was hoping adding some of the Server packages might help. No change though. I didn't enable the CentOS Extras repository. Either previously or this time. Each time I enable that it causes the installation to bomb out and I have to start over after anaconda starts sorting out dependencies. I mention that because anaconda does connect using my ethernet connection and verifies the repository successfully.

Literally, the first thing I did after completing the re-installation was pull up firefox. I didn't install it. And I still had the same problem as before.

After I made that last post I kicked off the package updater. That's running now. It just finished resolving dependencies and is a little more than halfway through downloading packages.

Incidently, I tried logging into X as root, which I don't normally do, and I still had the same problem. I'll try again after update completes without installing any additional software.

ifconfig and resolv.conf appear pretty much the same as they did on the previous install, I've copied those below. I don't know how to use or review iptables to look for specific problems with the firewall, but I'm starting to wonder about that.

I'm also still able to ping both google and centos.org, even though I can only access centos.org's website.


/sbin/ifconfig
eth0 Link encap:Ethernet HWaddr 00:1D:7D:D2:75:09
inet addr:192.168.0.3 Bcast:192.168.0.255 Mask:255.255.255.0
inet6 addr: fe80::21d:7dff:fed2:7509/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:67311 errors:0 dropped:0 overruns:0 frame:0
TX packets:39714 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:98679374 (94.1 MiB) TX bytes:3092009 (2.9 MiB)
Interrupt:58 Base address:0x2000

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:1589 errors:0 dropped:0 overruns:0 frame:0
TX packets:1589 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:3193172 (3.0 MiB) TX bytes:3193172 (3.0 MiB)

[john@localhost ~]$ cat /etc/resolv.conf
; generated by /sbin/dhclient-script
search domain.actdsltmp
nameserver 192.168.0.1
nameserver 205.171.3.65

After the update process completed and I rebooted, starting firefox forced a check to look for upgrades to add-ons. I haven't installed any, but this took 5 or 6 minutes to complete. After that I was able to connect to centos.org but not any of the problem sites. I decided to reboot again and this time when I started up firefox I was able to pull up every site I tried. google, redhat, oracle, jerrypournelle.com, etc. I closed the browser and restarted firefox and I couldn't get any websites to connect, not even centos.org. I rebooted again and now I'm able to connect to centos.org, but not much else besides tldp.org.

So now my connectivity appears to be intermittent. As I write this, I have another tab open trying to load google.com and it has timed out with the standard page load error.

Are you aware of anything that could cause intermittent problems? I went and re-seated all my cables between pc, modem and the wall. I also rebooted into Windows Vista and I still consistently have no issues at all there.

Thanks again.

Nothing short of confounding. Perhaps try the CentOS LiveCD. Sorry I don't know what else to suggest. The symptoms suggest something external, like at the ISP DNS level, but the success with Windows seems to preclude that. Hope somebody else jumps in with a fresh idea.

Have you tried with a different browser, eg Konquerer (part of KDE), or Opera (requires a download and install, if you can get to the Opera site).

Also, with Firefox, you haven't enabled a proxy; ie keep it as "direct connection".

Bill.

Thought of something else to check. What are your DNS servers for Windows? Any difference?

These are just wild shots in the dark, but maybe worth a try:

Power cycle the modem.

If the motherboard is an Intel G41 based chipset, make sure the BIOS is current.

Any strange entries in: /etc/hosts /etc/hosts.allow /etc/hosts.deny ?

Try 'mv $HOME/.mozilla $HOME/.mozilla.backup'

Giving OpenDNS a try might provide a little more trouble resolution.

Also, disabling IPV6 unless needed may help.