How to diagnose one user not able to reach my site?

Question

My site is www.trainerroad.com and lives on Azure.

I have a customer who get's

Oops! Google Chrome could not connect to www.trainerroad.com

When trying to access our website. Yesterday they could hit our site.

I had him do an nslookup and here's what he responded with:

Microsoft Windows XP [Version 5.1.2600] (C) Copyright 1985-2001 Microsoft Corp.
C:\Documents and Settings\FW_Front>nslookup www.trainerroad.com  
Server:  www   
Address:  10.1.10.1    
Non-authoritative answer:   
Name:    trainerroad2.cloudapp.net   
Address: 157.55.173.103   
Aliases:  www.trainerroad.com  

This all looks good to me. We have many other people currenly on the site from all over the world.

I also had him do a ipconfig /flushdns before the nslookup but that didn't help.

How do I continue to diagnose this issue?

Answer 1

We've addressed this from the other side on Super User as a Community FAQ:

How do I diagnose not being able to reach a specific website as an end user?

If I can generally reach web pages on the Internet but can't reach a specific one, how do I troubleshoot what the cause is as an end user?

You may find some of the tips over there useful for helping your client to debug the problem. Some of the suggestions:

• Make sure the site isn't down for everyone (done)
• Check that DNS resolves properly (done)
• Try a different browser
• Do a trace route and see if the connections time out somewhere along the way
• Make sure it isn't the router — try a different router, or try connecting at a friend's house
• Try a different DNS resolver (just in case)

Answer 2

Is it only in Chrome this happens? I would ask them to check in one other browser.

Could it be set up to live behind a proxy (that isn't getting hit by the nslookup)? Ask for maybe a print screen of their settings page.

Answer 3

When it is clear the issue isn't on your side (which by looking at your question it isn't) I would just suggest the customer to contact his IT department.

It could be anything (hosts file / firewall / proxy / something else).