andrew-mx-02.andrew.cmu.edu is an MTA. It is unlikely to have a web server running.
I telnet to this host on port 25 and I get the mail server's response.
On an Ubuntu or Debian machine, when I telnet to this host on port 80, I get, immediately:
telnet: Unable to connect to remote host: No route to host
On a Windows PC, I have to wait for more than 30 seconds before it says:
Could not open connection to the host, on port 80. Connect failed.
Is "No route to host" a correct description of the situation? ping responds nicely so certainly there is a route of sorts.
I am asking because I have a GoDaddy server connecting to andrew-mx-02.andrew.cmu.edu and giving this error response on port 25. From other servers it is fine. I would like to explain to the help desk accurately. If a firewall is blocking but they insist that the error message means I have not set up routing tables correctly, the problem will not be solved.
1 Answer
Most likely, this No route to host response is sent by the mailserver's firewall. Even iptables allows to do something like that, with --reject-with icmp-host-unreachable.
If port 80 is closed, with a host-unreachable policy, you will get a No route or similar response from any computer.
About port 25, things might be different. It needs to be open, since it is a mail server. However, your GoDaddy server may be blacklisted by IP by the mailserver. This is very common for dedicated servers that have fixed IPs. I rent an OVH/Kimsufi server that had its IP blacklisted in several places before I got it. You may also want to check what the reverse DNS of the IP is, because if it points to a blacklisted name the result will be the same.
Contact the helpdesk of the service you are trying to use, and:
- Give them the IP and domain name of your server,
- Tell them exactly what you tried on port 25 (telnet from your home works, telnet from the server doesn't)
- Ask them whether your server's IP is actually blacklisted,
- If yes, ask them why
- Tell them what you are trying to do, explain them why your server/application is harmless to them,
- Ask very politely if they can un-blacklist you
- Be very nice and polite, be precise without being verbose. Contacting helpdesks is an art that even the greatest have trouble mastering!
