Something pretty bizarre is happening here. I'm try to access a website from some machines inside my network and I just can't, while other machines access it normally. The website is online.sefaz.am.gov.br. In order to rule out all browser-related problems, I am testing this with telnet.
From my Macbook, I get this:
$ telnet online.sefaz.am.gov.br 80 Trying 220.127.116.11... Connected to online.sefaz.am.gov.br. Escape character is '^]'.
From a Windows XP box (Virtual Machine running on the Macbook), I get this:
C:\Documents and Settings\Administrator>telnet 18.104.22.168 80 Connecting To 22.214.171.124...Could not open connection to the host, on port 80: Connect failed
Note that on the Windows box I tried to telnet the IP address directly, so that rules out DNS issues. My anti-virus is disabled and so is the Windows firewall.
The virtual machine's network interface is bridged, so it gets a valid IP in my network. I noticed something pretty odd regarding that as well: if I change the network interface to NAT on the virtual machine, I can access the website normally.
I do have a domain controller in my network, but I'm not aware of any group policies that could block an IP.
So my question is: have you ever seen something like this? If so, how to fix it?
I ran nmap against the website from the computer that can't open it on the browser. Here's the outcome:
Starting Nmap 6.25 ( http://nmap.org ) at 2013-02-15 14:31 Pacific SA Standard Time Nmap scan report for online.sefaz.am.gov.br (126.96.36.199) Host is up (0.18s latency). Not shown: 996 filtered ports PORT STATE SERVICE 80/tcp open http 443/tcp open https 8080/tcp open http-proxy 8443/tcp closed https-alt TRACEROUTE (using port 8443/tcp) HOP RTT ADDRESS 1 ... 10 11 160.00 ms 188.8.131.52 Nmap done: 1 IP address (1 host up) scanned in 46.01 seconds
So I got one of these boxes that can't access the website and connected it directly to my internet link. Nothing changed. I still couldn't access the website. Then, I unplugged the machine from my network and connected it to the internet using a 3G usb stick. Guess what? It worked. So the logical conclusion would be that the problem lies on my internet link somewhere.
Not so fast... this very own computer I am typing from is using the internet link and can access the website normally. Go figure!