Why can't I connect to my server?

Ok, you've setup a host in our Dynamic DNS, Static DNS or Custom DNS service. But, you can't connect to this host using a web browser, ftp client, remote access software, etc. What is the problem?

Note: When we refer to a computer in this article, we're referring to any sort of device you might be trying to connect to. This might be a computer in the traditional sense, or it might be a DVR, web camera or some other similar device.
Check the IP address in our Database

The first thing to do is check the IP address which we're publishing for this host. You will this easiest to test while sitting at the computer you are trying to connect TO. Look at the host in your account and look at the value specified as the "IP in Database/DNS".

Is this the same as the IP address assigned to the computer you are trying to connect to (or your router if the computer is behind a NAT router)? If not, then you need to update the host to the correct IP address. If you have not installed an update client, you should do so now.

If you are not sure what IP address we should have for your computer, sit down at that computer, open a web browser and visit our CheckIP server. The IP address that this site shows is the IP address you should have configured for your computer in our system.
Check the DNS

Once you have verified that the IP address we have in our database is the correct one, make sure that you are getting the correct response from DNS queries. You will this easiest to test while sitting at the computer you are trying to connect FROM. We'll assume you have the command line program "dig" available to you (if you don't, get it).

Here's an example of what you might see:
$ dig example.dnsalias.org
;; ANSWER SECTION:
example.dnsalias.org. 14400 IN A 192.168.1.34

In the above example, 192.168.1.34 is the IP address which is being returned by the DNS query. Note the other number in the response, 14440. This is the TTL (Time To Live) of the DNS response. If the IP address in the response is not the same as the IP address we have in our database, the TTL is the number of seconds you can expect to have to wait before a DNS query will return the correct IP address. In the above example we've used a host configured in our Static DNS service which has a TTL of 4 hours (Dynamic DNS and Custom DNS use a 60 second TTL by default).
Check the router and/or firewall

Ok, you've made sure that the correct IP address is in our database and that DNS queries are actually returning the correct IP address. Time to check your router.

If the computer you are trying to connect to is behind a NAT router, make sure you have this router properly setup to route traffic to the computer. In particular, make sure that the specific port you are connecting over is being forwarded by the router to the computer. For example, if you are trying to connect to a web server, the default port is going to be port 80.

For more info on NAT, see our Dynamic DNS and NAT KB article.

Also, if you are trying to connect to the computer from either that same computer or from another computer which is on the same LAN (Local Area Network), you may be running into what is known as the loopback issue.

If you have a firewall (hardware or software) make sure this is setup to allow incoming traffic on the appropriate port as well. Note that some versions of Windows XP come with a firewall installed and turned on by default, so you may have a firewall without even knowing it.
Port Blocking by the ISP

Once you are sure that the IP address is correct in the database, DNS queries are returning the correct IP address and you have your router and/or firewall properly setup, if things are still not working, the problem may be that your ISP is blocking incoming traffic on the specific port you are trying to use.

This is most common for certain well known ports such as port 80 (used by HTTP) and port 25 (used by SMTP), but many ISPs block other ports as well.

If you have access to a command line on a remote machine, you can use the program "telnet" to test to see if the port you are trying to connect to is being blocked. The basic syntax is
telnet hostname port

Here is what it looks like when an ISP is blocking a port:
$ telnet example.dnsalias.org 80
Trying 192.168.1.34...
telnet: connect to address 192.168.1.34: Operation timed out
telnet: Unable to connect to remote host

Notice how the connections "timed out". While other problems can also cause this (such as a firewall on your end), this is often an indicator of the ISP blocking the traffic.

On the other hand, if you see this:
$ telnet example.dnsalias.org 45
Trying 192.168.1.34...
telnet: connect to address 192.168.1.34: Connection refused
telnet: Unable to connect to remote host

Notice how in this example the connection is refused, it doesn't time out. This is an indicator that the problem is on your end and not with the ISP.
Some specific solutions

In the cases of ISPs blocking port 25 and port 80, we offer solutions.
If your ISP is blocking traffic on port 25 such that you are not able to receive email sent to you, our MailHop Relay service can work around this.
If you are using our Dynamic DNS service and your ISP is blocking port 80, our free WebHop service can help solve this
And, finally, if you are using our Custom DNS service and you ISP is blocking port 80, our MyWebHop service (included with Custom DNS) can help solve this.