Response to the update: You're wrong (and this is one reason why you're reasoning is wonky on this entire thread). The OS is always listening to all ports on an active network interface. The decision on whether to pass a packet to a userland process listening to a specific port is taken after the packet is inspected by the routing and firewalling subsystems of the kernel (this is how it works on any sane OS anyway). You could theoretically create a userland process which is able to make this decision faster than the kernel subsystems but almost certainly only for the case of very overloaded (usually meaning crappily designed) firewall rulesets. You certainly won't be able to implement a service which inspects several packets (such as required for your protocol-specific request) faster than the kernel can inspect one. The kernel also still has to handle the entire TCP handshake process before handing the connection to your service, which is usually a far more resource-intensive process than dropping the initial packet at the firewall.

Also, from a network load POV, having nothing listening on a port is worse than a firewall blocking that port. A SYN packet (for opening a network connection) to a closed port (i.e. one without a listening service) requires the OS to respond with an RST packet. A well behaved remote network client will recognize that the port is closed and not try to send another SYN. A bot can/may/will just try again. In the case of an active firewall on that port no RST will be sent, thus you've halved the traffic on your network (disclaimer: I realise this last sentence is a very naive take on the subject, but it is valid in the context of this discussion).

Do a little research on basic networking (reading the Wikipedia page on TCP will already take you a long way) and you'll become much clearer on this subject.


All dogma is stupid.

In reply to Re^7: How to implement a fourth protocol by tirwhan
in thread How to implement a fourth protocol by Moron

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