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I am having a DNS issue with at least a couple of customers being unable to hit our website at all with chrome just reporting "This webpage is not available" (both over http or https), but DNS and network config is not my strong suit. says that it's up, and I know it works for some of our customers as I have the analytics that shows them logging in, but I am worried about how widespread the issue is.

All my DNS settings/CNAMEs/SSL stuff have been in place for a few weeks now, so I don't think it should be a DNS propagation issue.

How do I go about debugging this issue without access to the machines/networks that are affected? I am happy to ask my customers to run a few shell commands and send me the results (but I obviously don't want to hassle them too much) but I am not sure which commands would be the most useful.


The customers in question can see but not or

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Not a direct answer to your question, but and are really useful for finding DNS issues so if anything's wrong with your config it will most likely be flagged up by those – Smudge Jul 29 '11 at 11:23
It would be useful if you update your question with a few of the URLs or domain names where this problem exists. – wolfgangsz Jul 29 '11 at 11:26
@wolfgangsz done. – latentflip Jul 29 '11 at 11:29
up vote 1 down vote accepted

I can get to both the image and the login page without problems, which means your DNS setup and your website is working just fine.

Now that we have eliminated that, all that remains is local issues on your customer's side. It could be that they are trying to access your site through an HTTP proxy, which is either misconfigured or has an outdated cache. It is also possible that they have a strange DNS setup.

The first thing to do would be to ask a customer to open a command window (presumably they are mostly Windows users) and execute the commend nslookup This will either return the IP address of the server hosting the site or produce an error. If it produces an error or reports some other IP address, then DNS (at the customer site) is the problem. In that case you would need to speak to their sysadmin.

If this reports the correct IP address, then ask them to flush/empty the cache of their browser or try a different browser. Also ask them whether they have a proxy configured in their browser (details depend on the browser). In any case I would try and speak to their sysadmin.

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Well I have an nslookup for one customer which is indeed problematic: C:\Users\Anthony>nslookup Server: UnKnown Address: DNS request timed out. timeout was 2 seconds. DNS request timed out. timeout was 2 seconds. DNS request timed out. timeout was 2 seconds. *** UnKnown can't find Server failed So I guess I need to get on the phone to their ISP. – latentflip Jul 29 '11 at 11:42
Try their sysadmin first, and then the ISP. – wolfgangsz Jul 29 '11 at 12:10

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