[Twisted-Python] UDP File Copy

Tommi Virtanen tv at tv.debian.net
Thu Apr 7 04:14:08 EDT 2005

On Wed, 2005-04-06 at 11:18 +0200, Antoine Pitrou wrote:
> But the real difference here between UDP and TCP, is that when you open
> an outbound TCP connection, incoming TCP traffic will only be allowed
> *for that connection*. Whereas if you send an outbound UDP message, *all
> incoming UDP traffic* towards the originating address/port will be
> enabled (at least on some NAT boxes).
> This makes it easy for P2P systems to exchange messages between two
> NATted clients without any proxying/tunnelling mechanism: you just have
> to "punch a hole" by sending sporadic outgoing UDP traffic from your UDP
> socket and then you can receive all UDP traffic coming to that socket.
> You can't do that with TCP.

You can't do that with NATted UDP, either. Quite many firewalls
want to match all of the (srcIP, srcPort, dstIP, dstPort) to match.

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