On 6/29/20 3:47 AM, R.Wieser wrote:
> :-)  Look at the package-exchanging method I described.   Although the
> Pi is not attempting to do /anything/ to those packets, the end result
> is still that the data connection (between A and C) is scrubbed.
> Now, tell me if that means the Pi is "passive", or "active" :-)

The Pi is is actively doing something to copy packets from one socket to
another.  Packets won't flow between the sockets if there isn't
something doing the copy.  That something is the active part.

This is also why I think routers are active.  Same concept, just at an
interface level vs a socket level.

> IOW, the definition of the word "passive" (and "active" ofcourse)
> is strongly tied to the context:

Agreed.

> Using my described method to shuttle datapackets to-and-fro:
>
> - The Pi is passive because it does not initiate connections to either
> A or C

I agree that the Pi doesn't /initiate/ the socket connections.

But as previously stated, simply establishing a socket connection from A
to B and C to B is not enough.  Something on the Pi must copy packets
from socket to socket.  Thus why I state that the Pi is actively doing
something with the data on the sockets.

An analogy.  Suppose that two directors in the company have a Jr. staff
person go down and check their mailboxes in the mail room.  The first
director has the staffer take a memo and put it in the out box in the
mail room and check the first directors mail box.  The second director
does similar.  Without the 3rd employee in the mail room taking the mail
out of the out box and putting it in the respective directors inbox,
there will never be any mail for the staffer to pick up and bring back
to their respective directors.  This 3rd person, working in the mail
room, is actively doing /something/ with the mail.  What is being done
can be debated later.  But the fact remains, that without this 3rd
person actively doing something with mail, communications will not flow
between directors.

The Pi in your scenario is the 3rd person in the mail room actively
moving things between mail boxes.

As I type this, I realize that there is a slight variation that might be
what you're thinking.  If the staffers put the outgoing memos directly
into the recipient's mailbox (the staffers do the routing) there might
not be a need for the 3rd employee.  However, that is a different
process than is happening above.  It also requires that the staffer do
more work.  It also means that the staffers must have access to all of
the recipient's mailboxes.

> - The Pi is passive because it does not attempt to alter the
> datapackets it exchanges between the two sockets.

I disagree.  See above.  The packets (messages) don't go from one
mailbox (socket) to another without the mail room employee moving them.

The mail room employee does not need to open and scrutinize the
messages.  Something that would be invasive and extremely active.  The
simple act of taking messages from mailbox (socket) 1 and putting them
in mailbox (socket) 2 is an active process.  It's just less active than
reading and spell / grammar checking it.

> - From the POV of A and C the Pi is active, as it scrubs the datastream
> between them.

That's somewhat an incidental side effect that a shoe box shaped package
won't fit in a letter slot, thus gets dropped on the floor.

> I'm sorry, but I never mentioned anything of the kind  (I read that
> "actively decide" as "runtime" as opposed to "design time")

You have stated that only traffic of your choosing will be forwarded.
That means that there is a selection criteria to make the decision of if
something is forwarded or not.  Given above about the active mail room
employee, that is an "active decision" (per packet).

> Also, as we are observing nomenclature, what does "traffic" mean to
> you ?  Everything that goes over the ethernet cable (or comparable),
> or perhaps just the data thats left when all the different headers
> are peeled away ?  Maybe even something in between ?   And yeah,
> that does make (quite) a difference I'm afraid. :-)

Traffic is anything that the host sends.  Some of it will make it
through the Pi, some of it will not.  Depending on shape.

> And there you have yet another context in which "passive" or its
> counterpart "active" can be used.  On the other hand, can you make the
> RPi actually /do/ anything while its "passive" (not running any kind
> of program) ?   Other than being a paperweight of some sort I mean.

No.  The Pi won't do anything productive while being passive.  Even
running the kernel or receiving files into a queue is a form of active
action.  The Pi won't do anything when it's powered off, or in
paperweight mode.

> How do they detect that ?    You seem to assume that A and C know
> each others IPs.   Why ?   What would that be good for ?

Take a look at FTP and SIP for a couple examples.

> And even if they would know, there is no way they can reach each other.

You will see that FTP and SIP both want to connect to the address that's
inside the data that is passed, not the address of where the apparent
connection is coming from.



--
Grant. . . .
unix || die

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