on Sat, 6 Jul 2002
22:24:16 PST7
> As a matter of academic interest I would like to know how to do an IPTrace on the traffic between my
> SMC firewall and my ISP.
>
> When Adelphia took over my cable service I had to get a new cable modem. This one has lights that the
> one I had with Comcast didn't. One of those lights is an activity light the flickers even when all
> computers are off.
>
> I would like to know what my ISP and firewall are talking about.
Can I make a stab here? I followed the rest of this thread and it went off in
a direction related to the mechanics of your question (i.e., the how to) and I
think there is a simpler way to address the question. So, I came back to the
original question. Maybe, it'll start a new thread in which case I think you'll
get other information or else it'll die a horrible death, in which case it won't
interrupt the other thread.
I read the question as you wanting to know what communication is going on with
your modem-to-system connection when you're not doing anything even though there
seems to be quite a bit of activity. I think the answer is relatively simple.
Although cable is considered broadband like DSL, it probably has more in common
with satellite-type broadband than DSL. Cable (and satellite for that matter)
was originally designed to send signals unidirectionally and uniformly to all
subscribers. The latter half of that is the important part - every person was
supposed to get the same signal. So there's no real switching and
individualized routing - just amplifiers and splitters. DSL is different in
that it is like (and uses) the phone system. Communications are point-to-point
through the switch at the phone company. Everyone gets an individualized signal
from the sender (of which there can be many).
So, cable systems realized that they already had done the hard part - getting a
wire into each and every home. The question became how to graft an
individualized broad service onto what is essentially and hose that carries the
same flow to each house. The bottom line is that it became a universal
broadcase system in which the subscriber filters the signals at his end of the
cable. I'm not saying all communications go to all houses, but they do down to
the cable systems level of distribution, the neighborhood level where they have
their routers. All packets go to everyone in the neighborhood, and each
subscriber (his modem specifically) picks off the ones designated for his
address. That's why a cable system is basically a shared pipe which slows down
when everyone in the neighborhood decides they want to access the 'Net
simultaneously. On the other hand, when traffic usage is low, you can see
extremely fast download speeds - you're getting all the packets. What you're
seeing on the modem is the traffic generated by all of your neighbors. You
would be right in saying that it's not particularly efficient or secure but, on
the good side, you should get a good sense of what the traffic demand pattern is
in your neighborhood. :-)
This is a relatively simplistic description but I think it is reasonably
accurate.
See ya.
> Sheridan
-Rocky
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