Due to demand for the original PortCheck tool, I decided to release the updated version that I myself have been using that has a few more features to help diagnose connectivity issues.
The idea behind PortCheck was simple – help diagnose the common “page cannot be displayed” or “server not found” errors that could result from a number of network connectivity, or service availability issues.
In my post on the subject, Where did my IIS7 server go? Troubleshooting “server not found” errors, I listed some of the common causes for these errors, which include:
1) You misspelled the hostname
2) The hostname doesn’t exist
3) You are unable to resolve the server hostname to an IP address (DNS server connectivity)
4) You don’t have network connectivity to the server
5) Firewall is blocking your connection
6) IIS is not running
7) The Web site doesn’t exist
8) The Web site is stopped
9) The Web site does not have the binding on which you are trying to connect
The PING command is commonly used to help with 1-4, but when it comes to 4-8, it falls short because it doesn’t actually verify that the server is listening at the port at which you are trying to connect.
PortCheck bridges this gap by actually attempting to make a connection to the specified port.
In the current release of PortCheck, I added more diagnostics to help pinpoint the exact problem along the network route. The tool now does the following:
1) Resolve the address provided to all available IP addresses, and associated hostnames.
a. If failed, you have problems 1-3 on your hands
2) Attempt to connect to the specified port
a. If failed, PING the specified host
i. If failed, you most likely have problems 4-5: limited network connectivity, or firewall is blocking access (including ICMP). But, it could also be that firewall is blocking PING (ICMP), and you have problems 5-9 as well.
ii. If successful, you most likely have problems 5-9: firewall is blocking access to the port, IIS isn’t running, Web site is stopped or missing, or not listening at the specified address.
> PortCheck.exe zzz.mvolo.com 80
DNS LOOKUP FAILED (162 ms)
Most likely causes:
Host hostname / address does not exist (check spelling)
DNS is down or cannot connect to DNS server (try from another machine)
> PortCheck.exe www.mvolo.com 81
Resolved www.mvolo.com (220 ms)
CONNECTION TO www.mvolo.com:81 FAILED (21001 ms): A connection attempt failed be
cause the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond 188.8.131.52:81
PING REPLY (0 ms): TimedOut
The host may be unreachable. Most likely causes:
No network connectivity to host
No service active on that port
Blocked by remote firewall
Blocked by local or network firewall
Now, if PortCheck fails to make the connection, you still need to investigate what is happening at the server, which may require checking whether IIS is running, whether firewall is open, and whether the web site you are accessing exists, is started, and is listening at the right port. This requires administrative access to the server, and the steps you can find in Where did my IIS7 server go? Troubleshooting “server not found” errors.
In the next release of PortCheck, I will add some diagnostics that (assuming you are running as Administrator for the remote machine) can perform those diagnostics for you so the picture can be complete.
NOTE: PortCheck 2.0 is released under the MPL (Microsoft Permissive Use License).