Thanks for your kind word @happybeing. Yes, it was rewarding.
But I have to say I am a bit angry at all these test sites etc. that present the issue as if the ports could just lay open without an active listener! I mean I have encountered many sources about this subject matter aimed at laypeople, and none of them mentions this essential piece of information @Vort (and customer service of my ISP) gave me:
I have been demanding things that does not exist from my ISP, kind of. I feel sorry for the customer service peopleā¦
But yeah, I understand that your average layman is using port forwarding for services that are on all the time, so they can just check if their service works or not. My situation of having a service open once a week or less is very rare, for non-professionals at least.
Itās great to see people have ahah moments, especially when theyāve been struggling to figure something out.
I think the issue with those sites arises out of what they can say by probing a port. The result will either be āservice not availableā, āservice availableā or ācricketsā.
I donāt know the precise technical meaning of the terms those sites use, but I think thereās some confusion around what they mean (port open for ābusinessā) and what weāve been talking about on this thread (port forwarding). Forwarding at the the router doesnāt really mean the port is open from the point of view of a system probing the port. To consider it open, you really need to be able to detect something willing to do business on the other side.
man nc is very informative and once we have finished in the playground I am going back to basics to implement some of the possibilities shown at the bottom of that page.
I suspect it may lead to a couple of āa-haā moments for myself.
Definitely one of the more useful and accessible man pages.
Another layer of confusion comes from natural languages.
In finnish they talk about āporttiā when dealing with this thing, but that is a different word than āportā in english. But āporttiā means just simply and plainly āgateā, without any connotation of acton, such as āportingā etc. Itās very passive.
A proper translation of port is āsatamaā (harbour).
To āopen a gateā is quite different metaphor than to āopen an portā. For me opening a gate (portti) is about the same as āmaking a holeā, whereas opening a port (satama) raises more questions, maybe about actively receiving something.
