[PD] UDP server with Pd

[Roman Haefeli]

On Wed, 2021-06-02 at 17:29 -0400, Martin Peach wrote:
> 
> What is/are the issue{s} with firewall + NAT? Asking because I never
> used either, I only ever use them on a  LAN.

From what I know, NAT firewalls forward packets coming back from a
public server only when previously a matching packet was sent from the
client behind the firewall. They remember src and dst address of the
outgoing packets and forward packets from the server (with reverse src
and dst address) back to the client. If the client doesn't send
anything for a certain while, the firewall "forgets" about the
"connection". 

Client sends packet:
UDP(src:(192.168.1.33:55444) dst:(195.176.247.12:3025))

Firewall translates this to:
UDP(src:(81.4.3.1:55444) dst:(195.176.247.12:3025))

Server responds:
UDP(src:(195.176.247.12:3025) dst:(81.4.3.1:55444))

Firewall looks it up in its translation table and forwards it
to the local client:
UDP(src:(195.176.247.12:3025) dst:(192.168.1.33:55444))

If the server uses a different src address (for instance, different
port), the firewall simply discards the packet because it doesn't match
anything in its lookup table. 

Also, some firewall also translate the port number. Many try to keep
the port number, but that's not always possible, if - for example - two
different local clients use the same bind port for a connection to the
same destination address.

Roman




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