Ethernet jamming?

[myles.musser]

Hello everyone,

Am starting off on my CCNA studies, currently covering the core networking concepts. I just finished covering Ethernet material, which of course includes information on CSMA/CD, and had a question: would it be possible to attack a wired network to which you have access by flooding it with the jam signals that are used in response to collision detection? I've tried Googling the subject, but the only thing information can find on "jamming attacks" has to do with WLANs.

Thanks much!

[Ganesh Hariharan]

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Ethernet jamming?
Hello everyone,
Am starting off on my CCNA studies, currently covering the core networking concepts. I just finished covering Ethernet material, which of course includes information on CSMA/CD, and had a question: would it be possible to attack a wired network to which you have access by flooding it with the jam signals that are used in response to collision detection? I've tried Googling the subject, but the only thing information can find on "jamming attacks" has to do with WLANs.
Thanks much!

Hi Donald,

A jam signal is part of the Etherent CSMA/CD standard. Basically a station that sees a collision during transmission continues to transmit called "a jam signal" for a period of time to ensure that the propergation delay timer is met so that all stations on the collision domain see the segment is active/busy and reset their timers to wait/listen for quite/idle before they next transmit.

Hope to Help !!

Ganeshh Iyer

[Richard Burts]

Donald

Ganeshh has included a quote from some documentation in hopes of clarifying your question. But he has failed to point out one very important aspect of that quote. The "jam signal" is effective only within the collision domain. In the good old days of Ethernet based on coax cable (10BASE2 Ethernet and 10BASE5 Ethernet) you might be able to attack the network by sending a jam signal and it would impact all of the end stations on the network since all were in the same collision domain.

But in more modern Ethernet and especially in todays networks based on Ethernet switching, the collision domain is limited to the connection from the switch to your end device and your transmission of the jam signal would not impact any other devices in the network. So no you would not be able to attack the network by generating a jam signal.

HTH

Rick

[myles.musser]

Thanks so much to both of you. I figured switches would prevent that but thought it might still be possible for multiple nodes connected to a hub (logical bus).

Thanks again!

[Joseph W. Doherty]

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Yes correct, a hub should propagate the jam signal since it also acts as a shared Ethernet segment.