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    Force 10baseT Ethernet negotiation via cable?

    I have a bit of an unusual situation with Ethernet. We have a system that is using non-standard Ethernet cable for networking and it is auto-negotiating to 100baseTx-FD. The problem is at this link speed the system does not function correctly and has an unacceptable amount of packet loss. When we force the connection to 10baseT-FD using the mii-tool command in Linux the connection works with acceptable packet loss.

    The problem is that a software change is not in the cards as a way to make this work. So my question is this: does anyone know of a way to modify Ethernet cabling to force it to negotiate to a lower speed while not effecting the actual integrity of the cable to the point that it won't work at that speed either? I have been searching for something that would make this happen and so far I haven't found anything. I'm not sure this is even possible but you never know.

    Any thoughts, input or opinions are greatly appreciated.
    Thanks,
    Jeff Schultz

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    Re: Force 10baseT Ethernet negotiation via cable?

    Negotiation is performed at 10 MBit speed, based on the claimed capabilities of both peers. For this reason it's not checked if the cable provides sufficient signal quality at 100 MBit.

    If you don't want to touch the configuration of one of both endpoints and disable 100 MBit mode, you can connect the devices through a hub/switch that denies the negotiation protocol (like a legacy 10 MBit hub) or intentionally allow 10 MBit only.


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    Re: Force 10baseT Ethernet negotiation via cable?

    Interesting, I was under the assumption there was more to it than that since I've seen link speeds of 5mbit and lower in windows when connecting over long runs of Cat5. Maybe windows is displaying something other than what the link was negotiated to.

    Thank you for the information - even though it was not what I was hoping for.



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    Re: Force 10baseT Ethernet negotiation via cable?

    Can you use a shell script to automatically disable the auto-negotiate?

    http://www.cyberciti.biz/tips/howto-...permanent.html

    Open the file:
    # vi /etc/sysconfig/network-scripts/ifcfg-eth0

    Append following line:
    ETHTOOL_OPTS="speed 10 duplex half autoneg off"
    A best design is easily achieved with good test specs™
    A better question deserves a better answer. ™
    ... so include all your acceptance criteria ( values, % tolerance) and assumptions in your question or any design.

    ... Tony Stewart EE since 1975
    - slightly north of Toronto



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    Re: Force 10baseT Ethernet negotiation via cable?

    The negotiation method is described in IEEE 802.3-2008_section2, clause 28. http://standards.ieee.org/about/get/802/802.3.html



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    Re: Force 10baseT Ethernet negotiation via cable?

    Quote Originally Posted by SunnySkyguy View Post
    Can you use a shell script to automatically disable the auto-negotiate?

    http://www.cyberciti.biz/tips/howto-...permanent.html

    Open the file:
    # vi /etc/sysconfig/network-scripts/ifcfg-eth0

    Append following line:
    ETHTOOL_OPTS="speed 10 duplex half autoneg off"
    Unfortunately that becomes a software change which may then require re-certification for the system to be used the way we are configuring it.



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    Re: Force 10baseT Ethernet negotiation via cable?

    certification for what? not EMC I expect.
    A best design is easily achieved with good test specs™
    A better question deserves a better answer. ™
    ... so include all your acceptance criteria ( values, % tolerance) and assumptions in your question or any design.

    ... Tony Stewart EE since 1975
    - slightly north of Toronto



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    Re: Force 10baseT Ethernet negotiation via cable?

    Quote Originally Posted by SunnySkyguy View Post
    certification for what? not EMC I expect.
    This is for a modification to a fielded system so getting approval to deviate from what is currently being deployed is not always easy. If there was a way force the negotiation via hardware then we only have to certify that the hardware itself works as desired.



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