Traffic shaping - source vs destination port

[pquesinb]

Hi everyone,

So I'm new to OPNsense, having used pfSense and OpenBSD's pf quite some time ago, and I have a question about OPNsense's shaper.

In the following howto:
https://docs.opnsense.org/manual/how-tos/shaper_prioritize_using_queues.html

In setting up the rules for downloading traffic on the WAN interface, the reader is instructed to set the source port to the protocol for the traffic to be downloaded, as opposed to the destination port, which is set to any.  Using SMTP as the example here, is this because this howto assumes that one or more SMTP client(s) are on your network, having made connection(s) to an outside server at destination port 25 and the server will be sending data back to those clients with a source port of 25?  If you are instead running an SMTP server in your network, would you set this to destination port 25 instead?

I just want to make sure that I actually understand this, as opposed to only thinking that I understand it.

Thanks!

[pquesinb]

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