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8228 Views 3 Replies Latest reply: Nov 17, 2008 1:53 PM by cnewby RSS

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Router switch connection problems

Nov 15, 2008 12:02 PM

Neil Clark 6 posts since
Jun 24, 2008


Hi All,



Hope someone can give some advice. In my companys data centre i have had to run a Cat 6 cable between 2 floors, between two 2811 router and two 3750 switch. The cable run is about 94 metres. the 3750 switches on the first floor are in the same rack and the two 2811 routers are on the ground floor in racks that are directly next to each other. One of the routers gets a link connection but defaults to Half duplex even though both ends are configured to 100mb full duplex. the other connection will not come up. I have tested the cable with a cable tester and it shows all pairs are ok. When i plug the switch end into the cable tester and the other end into the router the router interface gives and UP/Down output.



i have had this working in the lab so i am wondering if the cable distance is actually slightly longer than 94 metres, however i have had no experience of what the problems are with connections nearing the 100 metre mark.



does anyone have any ideas??









  • Conwyn 9,683 posts since
    Sep 10, 2008
    Currently Being Moderated
    1. Nov 15, 2008 12:24 PM (in response to Neil Clark)
    Re: Router switch connection problems


    Hi Neil



    If it is possible take the switch or router into the same room. Connect with a short cable.



    If it not possible plug your PC into one end of the long cable and leave the other end in the router or switch.



    Alternative connect the CONS port on the switch router and connect your PC at the other end of the cable and see what happens to show runn command. Look for corruption.



    If OK its the long cable, the distance or EMI interference on route. I would go for EMI






    Regards Conwyn



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  • Scott Morris - CCDE/4xCCIE/2xJNCIE 8,429 posts since
    Oct 7, 2008
    Currently Being Moderated
    2. Nov 15, 2008 10:03 PM (in response to Conwyn)
    Re: Router switch connection problems


    There's LOTS of things that could be going on from a cabling perspective.



    When doing cable installation, simply mapping out the pairs is nice (and I'd say a good first step to avoid most lunatic fringe situations) but it doesn't do anything to the TRUE capabilities or certification of the cable itself.



    A REAL cable tester is needed for that. For 100M, you could even find any of the old Cat5 testers (EBay's good if you don't own one already and don't want to purchase a new one). They'll still test Cat6 cable just fine, you just won't be able to test to the full potential capacity of the cabling!



    But baseline certification for your requirements is paramount!












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  • cnewby 75 posts since
    Apr 21, 2008
    Currently Being Moderated
    3. Nov 17, 2008 1:53 PM (in response to Neil Clark)
    Re: Router switch connection problems


    Hi Neil,



    I believe the 3750 switches have built in TDR (Time Domain Reflectometer), which could provide some insight into what's going on. Check out the url






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