tracing where a network blockage occurs

I have a customer that is having trouble accessing my server. They can hit the server by entering

The transmissions do not even make it to the firewall if they enter

Any Ideas on how to trace this network blockage?
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"The transmissions do not even make it to the firewall if they enter"

That sounds unlikely (although not impossible) - how exactly have you verified that?  Is it just one customer, or all?


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these websites are having ip's so ask the customer to do a traceroute to those ip's, if icmp is not blocked then you should be seeing where the packets are getting dropped. It should be the firewall somewhere.

generally the webservers or the firewalls would be blocking icmp traffic, you got to open them for testing.

nmap is a free utility that if run in your customer machine towards your server ip, would show you which ports are accessible for your website from your customer machine.

e.g nmap <your webppage/server ip>

Steve JenningsIT ManagerCommented:
I have to agree with The--Captain. Well, more or less. I can't imagine a scenario where that would happen under "normal" technical circumstances by which I mean nobody is deliberately trying to block that particular URL. Entering those two slightly different URLs but with the same domain would not affect a DNS response unless someone between Customer and you has a really screwed up DNS or unless the customer has a hosts file that looks like:


That said, if someone had a load balancer set up to route based on URL and that particular URL wasn't defined it would be dropped.

So how DO you know that it doesn't make it to the firewall? Are you able to trace traffic inbound on the firewall interface?

Good luck,
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jimmylew52Author Commented:
Thank you for the input. We will never know the truth about the problem. The customer says the problem mysteriously went away. I do know he talked to the firewall guys at his company and they claim not to have changed anything. I also found out that the client was doing the testing from two different servers not the same one, explaining the connection to the url sometimes.

jimmylew52Author Commented:
thanks again
This happens to me all the time.  Problems with remote sites connecting mysteriously vanish when I threaten to break out the sniffer ;-)

People will lie when they find the problem was on their end, but don't feel like admitting it (I'm guessing they don't really understand computers that well and think they're kind of magical and random, and hope I do too.  I do not).  I just put a note in their file saying that they have random problems to which they do not like to admit.
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