Same port when you pass socketDescriptor?

[Dumbledore]

If you have a QTcpServer and you pass off a new connection to its own thread. Does this also communicate on some random port? Or is it the same port as the listener that this connection is established?

If it is a different port, how do you deal with firewalls?

[wysota]

If you have a QTcpServer and you pass off a new connection to its own thread. Does this also communicate on some random port? Or is it the same port as the listener that this connection is established?
It's a different port.


If it is a different port, how do you deal with firewalls?
You don't. Firewalls should track connections and pass such traffic that was established on another port. At least that's what the TCP protocol says :)

If you use iptables, a rule similar to:

iptables -I INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT

should be present in the firewall for tcp traffic to work properly. If you're not a firewall admin, you needn't care.

[Dumbledore]

Wow, I didn't know that! My firewall is implemented through my router. So I imagine it is designed to follow the TCP specification and I needant worry?

[wysota]

Yes, that's correct. Otherwise you wouldn't be able to post on this forum :)

BTW. This is completely invisible for all the software - that's the intention of the mechanism. It's even hard to say the socket is related to any "port" - the server just gets another socket and it sort of works (the client still sees it as the port it connected to, but there is another socket listening on that port).