Re: Unused cables left in router?

Discussion in 'Computer Support' started by Mike Easter, Jun 27, 2010.

  1. Mike Easter

    Mike Easter Guest

    wrote:
    > I have a Linksys N router. I have my main desktop hooked into it as well as a
    > cable which runs to a Sony Blu-ray player which networks with YouTube, Netflix,
    > etc. I was recently using a second computer to find some old files, so I also
    > hooked it up to the router. Before I put the old system away and disconnect the
    > cable from the router, I was wondering (as it's a little difficult to aces my
    > router on top of my computer hutch) is there any harm in leaving the cable
    > plugged into the router at one end and the other end going unused until I want
    > to hook something up to it again? Thanks.


    I've heard that unterminated ethernet cables can be associated with
    collisions caused by reflections, but I'm no expert on that hard core stuff.

    If you search on 'unterminated ethernet' you will run into discussions
    about collisions or diagnosing causes of collisions.

    Cisco talks about using a TDR - timed domain reflectometer - to diagnose
    reflection related collisions and to look for unterminated ethernet cables.

    I don't have a link that explains it nicely, so I'm not sure. I do know
    that I once had some mysterious problems and I was talking to a
    networking tech about 'things' and he told me to not do that.

    After I removed the unterminated cable from the router and powerup
    rebooted everything, the problem went away -- but that story doesn't
    actually prove anything.

    In that case, the unterminated cable was about 25 feet long.


    --
    Mike Easter
    Mike Easter, Jun 27, 2010
    #1
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  2. Mike Easter wrote:

    > I've heard that unterminated ethernet cables can be associated with
    > collisions caused by reflections, but I'm no expert on that hard core
    > stuff.
    >
    > If you search on 'unterminated ethernet' you will run into discussions
    > about collisions or diagnosing causes of collisions.
    >

    Well, yes, but we actually have a switch with four or more electrically
    separated output ports. Unused ports are simply "turned off" or on
    standby. The switch simply doesn't deliver a signal there since there is
    no target MAC address associated with a unused port.
    wisdomkiller & pain, Jul 2, 2010
    #2
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  3. Mike Easter

    Mike Easter Guest

    wisdomkiller & pain wrote:
    > Mike Easter wrote:
    >
    >> I've heard that unterminated ethernet cables can be associated with
    >> collisions caused by reflections, but I'm no expert on that hard core
    >> stuff.
    >>
    >> If you search on 'unterminated ethernet' you will run into discussions
    >> about collisions or diagnosing causes of collisions.
    >>

    > Well, yes, but we actually have a switch with four or more electrically
    > separated output ports. Unused ports are simply "turned off" or on
    > standby. The switch simply doesn't deliver a signal there since there is
    > no target MAC address associated with a unused port.


    There used to be a target MAC address there. My router remembers MACs
    and names of targets even when they are 'turned off' - until it is
    powered down or software reset. How does the router of the OP know
    whether or not the Sony blu-ray player is still there or not?

    I have a router and also a smart switch nearby. Every ethernet port
    which has 'something' connected to it has a light on, even if there is
    no activity on that port because the machine is off.

    Perhaps you are proposing that he can leave the ethernet cable attached,
    but he should reset the router after removing the player so it the
    router will 'know' - find out - that there is nothing there now.


    --
    Mike Easter
    Mike Easter, Jul 2, 2010
    #3
  4. Mike Easter wrote:

    > wisdomkiller & pain wrote:
    >> Mike Easter wrote:
    >>
    >>> I've heard that unterminated ethernet cables can be associated with
    >>> collisions caused by reflections, but I'm no expert on that hard core
    >>> stuff.
    >>>
    >>> If you search on 'unterminated ethernet' you will run into discussions
    >>> about collisions or diagnosing causes of collisions.
    >>>

    >> Well, yes, but we actually have a switch with four or more electrically
    >> separated output ports. Unused ports are simply "turned off" or on
    >> standby. The switch simply doesn't deliver a signal there since there
    >> is no target MAC address associated with a unused port.

    >
    > There used to be a target MAC address there. My router remembers MACs
    > and names of targets even when they are 'turned off' - until it is
    > powered down or software reset. How does the router of the OP know
    > whether or not the Sony blu-ray player is still there or not?
    >

    We have a big building with a dozen or so 24/48port ciscos. And lotta
    cables running there unconnected on the other side.
    MAC addresses are remembered for adjustable time but the switches do know
    and show on leds, where a device is connected or not.
    Even workstations turned-off do have their NIC online from standby power,
    to enable wakeonlan.

    > I have a router and also a smart switch nearby. Every ethernet port
    > which has 'something' connected to it has a light on, even if there is
    > no activity on that port because the machine is off.
    >

    Unplug the "something" from the mains. You will see the leds (if present)
    near the rj45 connector go dark - and the corresponding light on the
    switch as well.

    > Perhaps you are proposing that he can leave the ethernet cable attached,
    > but he should reset the router after removing the player so it the
    > router will 'know' - find out - that there is nothing there now.
    >

    Not necessary.
    wisdomkiller & pain, Jul 3, 2010
    #4
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