Once in a while administrators are asking themselves, why the use of p2p Applications like Skype is possible in their networks with a Firewall blocking all incoming traffic.
I’ll try to explain this in a simple way. The mentioned Applications are no ‘real’ p2p Apps, because they’re using a Server to establish the connection.
So what happens when Alice (IP 10.0.0.1) wants to call Bob (IP 11.0.0.1)? She sends a request to the Server, who’s requesting Bob and informs him about Alice (her IP and Port she wants tu use, let’s say 2020). As a result, Bob sends a UDP message to Alice on that Port. While Alice’S Firewalls drops this, Bobs one is in a state where it accepts replys from Alice on this Port. Alice does the same now, and we have two Firewalls, both Accepting communication over this „Connection“, thinking they’re accepting answers to former requests.
This uses the feature of many Firewalls to treat UDP as „statefull“, thinking that packets with corresponding ports and addresses are belonging to the same connection, what can be a mistake. This is different to the TCP Protocol, where there’s a real, reliable creating of connections.
So one should think twice before allowing all outgoing traffic, because this can have strange side-effects.
My first credit card! I dream of it as nobody would approve me! Please advise what to do – I applied so frequently my score is almost at ground… My friend said that Bank of America issues cards for students ansd I need one for purchases. My college mate is suggesting a web site but I don’t believe it.
balance transfers and credit score
deborah am 2007-12-11