Re: CSMA/CD
From: Adam Balogh (adam_at_vattnet.net)
Date: 08/22/03
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To: Security-basics@securityfocus.com Date: Fri, 22 Aug 2003 03:40:05 -0500
On Thu, 2003-08-21 at 20:12, David Nichols wrote:
> You are talking about two different things. Ethernet, and TCP/IP. Even
> thought the combination of the two is the most common today, they are not
> the same thing. You can run TCP/IP over token ring, or IPX/SPX over
> Ethernet. Basically Ethernet (or Token Ring) are layers 1 and 2 while
> TCP/IP (or IPX/SPX) are layers 3 and above.
> You wouldn't re-write the TCP/IP stack, but the device driver for the
> Ethernet card. Even thatmay not work because the CSMA/CD may be done
> entirely in hardware on the card
>
> Working-on-my-CCNA-as-well-ly
> David Nichols
>
> ----- Original Message -----
> From: ". ." <ajfomania@hotmail.com>
> To: <Security-basics@securityfocus.com>
> Sent: Thursday, August 21, 2003 7:08 AM
> Subject: CSMA/CD
>
>
> > Hi there!
> > I'm currently reading a CCNA book, and I've got some questions I can't
> find
> > an answer to.
> > The Carrier Sense Multiple Access with Collision Detection checks if
there
> > is any traffic on the wire and then starts to send the host's data, if
> > someone tryes to send at the same time, the sending host sends the
> "trying"
> > host a jam signal that would make the trying host to wait.If the trying
> host
> > get's 15 jam signals at one time, it times out.
> >
> > Some questions came up at this chapter. Is there any possibility to
write
> a
> > program that sends jam signals to other hosts within the same broadcast
> > domain until they timed out and died ? Does this mean that IF you where
to
> > write this program, actually needed to rewrite a part of the tcp/ip
> > protocol stack ? Isn't this a big issue?
> >
> > Sorry for my bad english..
> >
> > Best Regards: Fredrik Wessberg
> >
> > _________________________________________________________________
When a nic receives a jam-signal it randomises a number between 1-65536
ns/us(don't recall/depends on nic). This is a delay it uses before it
resends the package. The chances that 2 nic's randomises the same number
15 times is indeed minimal. This hasn't really anything to do with
TCP/IP since this in layer 1 and 2.
/Adam
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