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Some Outbound TCP/IP Addresses are blocked - why?

Posted on 2013-11-07
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Last Modified: 2013-11-11
At one of my clients locations they can not browse various websites.
For example at this particular location they can browse to google but not www.dahats.com.au which is their website.

What could be causing this?

DNS does resolve the IP address correctly.

This is a relatively recent issue.  Previously they could browse any website.
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Question by:enigmasolutions
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Expert Comment

by:Dave Baldwin
ID: 39632771
What error message do they get?  You might check anything that might do content filtering like their anti-virus or firewall.
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Expert Comment

by:Qlemo
ID: 39632896
Content-filtering is my first guess, too.
Did you check whether packets can pass to the destination, e.g. with  tracert -d -h 6 -w 100 www.dahats.com.au?
First point to check is (of course) the corporate firewall. A personal firewall, if active, could be an issue too.
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Author Comment

by:enigmasolutions
ID: 39636406
Thanks Qlemo,

Actually I did ask them to do a tracert www.dahats.com.au and as far as I know they got the same results that I got.  But I was able to view their website and they were not.

I will get a screen shot of the tracert with the options suggested.
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Qlemo earned 500 total points
ID: 39637040
If a tracert to the target worked fine, there is no need to do it again; my additional options are only for speeding up the test (no reverse DNS, only 6 routers, 100ms timeout).

The ICMP packets are passing, so it is very likely a content filtering or port blocking issue (for specific IP addresses). The only point you can know about that is their firewall; its logs might show the reason.

If you want to, you can try  telnet www.dahats.com.au 80   and then type something invalid. After pressing return you should get a HTTP/1.1 400 Bad Request message. If that does not work from their network, the HTTP access is blocked for that IP. If you get the Bad Request message, content filtering prevents seeing the page.
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Author Comment

by:enigmasolutions
ID: 39637791
Thank you Qlemo,

The problem seems to have fixed it self.  Or at least we don't really know what was the cause.  

Anyway the client did this:
* Disconnected the router form the internet (I think hit disconnect in router setup)
* for some reason router lost its username / pwd (so they re-entered it)
* it also lost port forwarding settings
* After restart - all working

Perhaps a fault router?  (Linksys).
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Expert Comment

by:Qlemo
ID: 39638217
A router loosing the settings on disconnect or reboot? Very suspicious ...
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Author Closing Comment

by:enigmasolutions
ID: 39638339
Although not the specific solution, all responses helped resolve the issue.   Thank you.
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