DNS resolution issues

[dougcvd]

I am relatively new to linux, though I have worked with computer many years starting with DOS and up.



I am having an issue with getting my linux test servers to reach the outside world. I have servers set of with PClinux, CentOS, and Ubuntu. Currently the issue is with the CentOS box. I have set up my onboard NIC with the LAN TCP/IP parameters ans well as the DNS Server addresses through the GUI. I have verified that they are correct but I cannot access a URL through a browser (Firefox). From a Terminal window I can PING an external site via both its IP address AND its URL. In other words, I can PING 174.132.123.98 AND linuxforums.org sucessfully. However, if I open up a browser I can only access the same web site with the IP address and NOT the URL.



Here is my question; where can I find a reference of Terminal commands whereby I can test the various aspects of the TCP/IP stack and manually configure my NICs using command line commands instead of using the GUI which does not want to play nice.

[billollib]

The basic tool for looking at tcp traffic is tcpdump. You can also try ethereal or it's successor, Wireshark. Just for giggles, I also usually install etherape, but just because I like the graphics.

Basic tools for DNS stuff include netstat, nslookup, and dig. Other tools to look at are dnswalk, nlslint, and dnsadmin.

[dougcvd]

Thank you for your assistance

[Lazydog]

Is there a proxy server that you need to add to your web app? Reason I ask is because you stated that you can ping the site by both ip and url which tells me that DNS is working. Things I would be looking at are proxy and/or firewall.

[billollib]

Lazydog writes: "Is there a proxy server ..."

I second that. A *lot* of my issues with selective filtering (which is what this sounds like) has to do with port forwarding or other router configuration issues. More important, you might check on the default configuration of iptables in your distro. I know that the default for my distro is to deny just about everything.

[Lazydog]

I know that the default for my distro is to deny just about everything.

Are you sure about this? Most distros will block all NEW connection coming in but ones leaving should be allowed by default.

[billollib]

You're right. I misspoke. I was thinking about a small network I set up recently at an in-law's place where I replaced all the boxes at the same time and none of them could talk to each other. I assumed that it was a network issue until I thought about looking at iptables. Doh. That was about three hours wasted. The other time I wasted a few hours was when I had port forwarding misconfigured on my firewall and was sending requests to a nonexistent machine. I must have looked at the list a hundred times before I noticed it -- it's odd how often I see what you think *should* be in those tables rather than what really *is* in the table.