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Thread: Network cable works with Hub, but not with Switch or Router

  1. #1
    Junior Member
    Join Date
    Feb 2008

    Network cable works with Hub, but not with Switch or Router

    Hi everyone,

    My current setup:

    Cable Modem --> Hub --> 2 computers (PC1 & PC2)

    PC1 is right next to the Modem/Hub connected with a store bought professionally-made CAT5 cable.

    PC2 is connected by a cable that runs across the house that someone made for me probably 7 years ago, and it must be about 20 meters long. This is what it says on the cable:

    "24AWG UTP 100 OHMS=200 MHz PVC CAT5"

    Now here's the problem, when I connect PC2 to the Hub it establishes a connection to the internet. But if I try to use a Switch or a Router instead of the Hub, PC2 fails to establish a connection. PC1 with the professionally-made cable establishes a connection in all three situations.

    Is there any reason why a network cable would work with a Hub but not with a Switch or Router? Is this something that could happen with a crossover cable? (even though I don't know if this is a crossover cable)

    Any clue would be very appreciated!


  2. #2
    Switching & Routing Nerd cchooper's Avatar
    Join Date
    Oct 2003
    Southern Oregon
    Yes, it's possible that you have a crossover cable. The reason why the hub might work and the switch doesn't is that you may have a hub capable of Auto-MDIX, whereas your switch isn't. Auto-MDIX essentially allows a hub or a switch to detect the type of cable being used (crossover or straight) and modifiy its internal wiring accordingly.

    Take a look at the connectors on the cable, if the order of the colored wires is identifical then it is not a crossover cable, but if the pairs 1/2 and 3/6 are switched then it is a crossover cable. You can use this image as a guide, but remember that it's not the colors that are important, but the location of the pairs:
    Hacking router firmware since 2005

  3. #3
    Junior Member
    Join Date
    Feb 2008
    Thanks for your reply.

    I will have a look at the connectors on both ends of the cable, might have to get a magnifying glass to do that...

    I was under the impression that more recent routers could auto-detect a crossover cable and accommodate it.. I tried it with a WRT54G. I don't remember the brand/model of the switch.

    I don't have the router or the switch anymore, so I'm going to try my luck with a router again (ordered an SMC7004VBR) because I need to connect a 3rd pc and my ISP only provides two IP's (I'm using ICS temporarily).

    I'll report back.

  4. #4
    Advanced Member
    Join Date
    Dec 2001
    Most newer technology (switches, routers, etc.), especially consumer grade stuff, does do auto MDX. That doesn't mean it always works properly.

    You could also have a bad cable, so try a known working cable to at least rule out the possibility. Could also be the cable wasn't run to spec and some noise is getting into it that causes the switch or router to fail, but doesn't bother the hub.

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