Re: CSMA/CD

From: Adam Balogh (adam_at_vattnet.net)
Date: 08/22/03

  • Next message: Attila Nagy: "Re: Network IDS" 
    To: Security-basics@securityfocus.com
Date: 22 Aug 2003 10:40:05 +0200

    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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  • Next message: Attila Nagy: "Re: Network IDS"

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