RE: CSMA/CD

["Stuart" <secmail () patchsupplier dyndns org>]

So technically, a specially crafted cat5 cable with rj45 jack connected
to a hub with some sort of power source active to send the same amount
of voltage as a network card on the send line of the cable would disrupt
the collision domain?

Stu

-----Original Message-----
From: Greg Holl [mailto:gholl () tp devry edu] 
Sent: 22 August 2003 05:10
To: Security-basics () securityfocus com
Subject: RE: CSMA/CD


> > Does this mean that IF you were to write this program, you'd actually

> > need to rewrite a part of the tcp/ip protocol stack?

>  As someone else has pointed out, this is probably normally done as
part of the Ethernet >port hardware.  At best, it might be in driver
code.  Since Ethernet can be used to carry >AppleTalk, DECNet, IPX, etc,
it's not in the TCP/IP part of the stack.

This is done at the hardware level.  Think of the OSI model.  Collisions
take place at the physical layer.  CSMA/CD is an access methodology,
which is located at the physical layer.   Appletalk, DECNet, IPX,
TCP/IP, etc are suites of protocols existing at layer 3 and above.   You
can technically run these protocols on a CSMA/CA network (i.e. Token
Ring), because the protocol stacks don't really care what is happening
at the physical layer.  So, like David said, the closest you could come
to this type of disruption would be a DoS attack (which is generally a
layer 7 occurance).

-Greg

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Attend Black Hat Briefings & Training Federal, September 29-30 (Training), 
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