Network programming on java

Question

I have written a simple network program on java using sockets. Program has a client and a server.

When user types a word on client side, server simply return this word to client.

On server side I use Serversocket and bind it to port 4444. Why does not firewall block this connection on my server PC?

I ask this question because earlier I wrote this program using corba technology, and firewall on my server PC was blocking the connection to this port; when I disabled the firewall the program worked fine.

By any chance is this a single box experiment ? Some firewall packages on some operating systems do not get invoked for local sockets. — Jim Rush
– Jim Rush, Commented Dec 25, 2010 at 17:02
Are you running client and server on the same machine? Firewall does not usually block to localhost connection. — gigadot
– gigadot, Commented Dec 25, 2010 at 17:03
This doesn't appear to be a question about Java, instead the question is how your unspecified firewall software works. i.e why does it block this but not that. — Peter Lawrey
– Peter Lawrey, Commented Dec 25, 2010 at 17:32
@oluies winXP and standart windows firewall @Jim Rush & gigadot I have tested it on different machines — maks
– maks, Commented Dec 25, 2010 at 17:46

DwB · Accepted Answer · 2010-12-25 17:31:53Z

2

My first guess is that your firewall is only blocking well known and/or well known and registered ports. Check out this wikipedia article. To test this, have your program bind to a well known port and / or a registered port that is not in use in your environment.

answered Dec 25, 2010 at 17:31

DwB

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maks Over a year ago

A few minutes ago I tested it with port number 21, but program with sockets worked well and corba program didn't work until the firewall was enabled

Daniel · Accepted Answer · 2010-12-29 08:11:21Z

1

Maybe your firewall doesn't block the opening of server sockets, but only the connections to them? In this case you would be able to connect to the socket over "localhost", but not on your external IP (which means the IP on your local network, not the one at your router).

answered Dec 29, 2010 at 8:11

Daniel

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