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From "Turner, John" <>
Subject RE: Can´t access Tomcat from outside router, help !
Date Mon, 13 Jan 2003 13:31:28 GMT

If you port scan your public IP address from a computer known to be external
to that IP address, and you don't see port 8080, then my guess (99%) is that
your ISP is blocking ports on the router "upstream" from yours.  That is, it
doesn't matter what port you open on your router, traffic will never be
routed to it.

The simplest thing is to get on a computer known to be external to your
public IP address, get to a command prompt (any OS is fine) and type:

telnet your-public-IP 8080

If you don't get a response back, your ISP is blocking that port for
whatever reason, and you can't do anything about it.  That, or your router
is messed up.

If port 8080 is available on that external IP, you should see a response
like this:

Trying your-public-IP...
Connected to your-public-IP.
Escape character is '^]'.

At that point, even if you can't see characters echoed on the screen, you
can type:

GET HTTP/1.1 <return>

And you should see a Tomcat error message, in plain text.

You can try this using your internal IP from another computer, too, though
we know that works already.  In any case, if Tomcat is up on your internal
net, but not external, either your D-Link router is messed up, or your ISP
is blocking that port on your public IP, and probably a whole range of
others.  If your ISP is blocking that port, you can 1) talk to them and try
to get them to unblock it (good luck!), 2) install a connector like mod_jk
and skip worrying about 8080, or 3) dump Apache and run Tomcat on port 80.


> -----Original Message-----
> From: 
> []
> Sent: Monday, January 13, 2003 3:10 AM
> To:
> Subject: SV: Can´t access Tomcat from outside router, help !
> I have registered a dynamic dns (like, but this 
> is not of value in this case since I use the ip to when testing.
> The router is a D-link 804, which I have configured with open 
> ports on 22, 80 and 8080. And I have also enabled 
> port-forwarding on these port to the proper computer on the lan.
> The computer hosting apache and tomcat is running linux mandrake.
> If I portscan this machine from another computer on the lan I 
> can see that port 22, 80 and 8080 (and some other ports) are open.
> If I portscan my public ip from outside (ie the internet) I 
> can only see port 22 and 80 (not 8080 even though I have 
> opened the port in the router and anabled port forwarding).
> If I try to connect to apache and tomcat from the lan it 
> works fine, I get a repsonse from both services. If I try to 
> connect to them from the internet I only get a response from 
> apache, nothing from tomcat, and nothing shows up the the tomcat logs.
> /D

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