🚀 go-pugleaf

Cable does not use CSMA/CD.  It has always, including the proprietary Motorola system,
used polling for the upstream channel.

If you were to sniff on your cable, you could only see the downstream transmissions,
and the upstream transmission of those on your side of the next upstream amplifier.
There is no promiscuous mode on a DOCSIS modem, and you would have to be able to
decode the encryption, which so far as I know is used universally.

Thanks for listening.

Kip Patterson

Lawrence Baldwin wrote:

> John Navas wrote:
> >
> > [POSTED TO comp.dcom.modems.cable; PLEASE REPLY THERE]
> >
> > In <3A76B6CA.73B36B26@mynetwatchman.com>, Lawrence Baldwin
> > <baldwinlSPAMMENOT@mynetwatchman.com> wrote:
> >
> > >I actually contend that DOCSIS cable (assuming encryption is turned on) is more
> > >secure than DSL.  Since DSL isn't encrypted, it can be packet sniffed at
> > >any (relatively unsecured) cross box or pedestal, albeit with a VERY expensive
> > >analyzer.
> >
> > Am I missing something, or are you just referring to encryption between
> > the cable modem and the CMTS?
>
> Absolutely.
>
> > If the latter, then traffic beyond the
> > CMTS is unencrypted, and just as exposed as DSL traffic.  Both are
> > secure on the local link;
>
> ADSL sure isn't secure on the local link, for reasons above.
> If typical cable modem isn't encrypted, than agree it's equally
> insecure.
>
> What irks me is when ADSL providers say: "ADSL is more secure than
> because your connection
> isn't shared between your home and central office".  I think it's
> ridiculous to associate *shared* with *insecure* without obviously
> taking the time to understand the issues.  Even worse, they're inferring
> that the *unshared* = *secure* (from all threats), which is dangerously
> mis-leading.
>
> I doubt packet sniffing the local link is a big concern anyway, so this
> is really pretty moot.
>
> I guess my only big concern would be with cable modem...I've heard that
> the modems get be put into an promiscous
> debug mode and and start forwarding *all* traffic out the Ethernet
> port.  This would be a real threat as it means
> anyone with a shareware analyzer could Sniff.  If this isn't possible,
> then you'd need a broadband analyzer, which would be out of most people
> reach.
>
> >both are exposed on shared links beyond the CMTS/DSLAM.
>
> Agreed.  But presumably access to network infrasture is physically
> secured at these layers.  Anybody can walk up to a pedestal and cross
> box and jack in without much trouble.
>
> >
> > I agree that most broadband ads are colorful nonsense.  Nevertheless,
> > there is a real and important difference -- when the uplink saturates on
> > the typical consumer asymmetrical TCP/IP connection, downlink speed
> > takes a big hit down to about the uplink speed (e.g., your 128/1500
> > service suddenly becomes 128/128).
>
> OK, but what percentage of users are impacted by this.
>
> > On DSL, that affects *only* the
> > subscriber's own downlink; on cable, that affects *all* subscribers on
> > the shared segment.  It's the big dark secret that cable MSO's don't
> > want to talk about, and the probable reason that servers are typically
> > prohibited on cable, even with an uplink cap, but not on DSL.
>
> HUMMMM. VERY interesting point.  Basically one porn server in the
> "neighborhood"
> and the whole darn thing is down even though there's tons of downstream
> bandwidth
> available. ....hmmmm.... DSL is looking better and better every day.
>
> I have no hands-on experience with cable infrastructure internals, but
> a lot of what you content would seem to depend on how cable is
> throttled.
>
> I know that DOCSIS has the *capability* of defining transmission slots
> such
> that the cable is no longer a CSMA/CD shared Ethernet...however, I'm
> pretty
> sure that almost no one implements this.  Anyone know for sure??
>
> --
> -------------------------
> Lawrence Baldwin
> Protocol Scientist
> 678-624-0924
> http://www.mynetwatchman.com - I'm under attack, now what?