WAN Link - Half Duplex

Posted on 2012-09-04
Last Modified: 2012-09-06
Hey Guys,

We have a Metro Ethernet wan connection which seems to be auto negotiating at 100 half duplex. When I set the port to force 100/full the line protocol is down, when set it to 100/half or back to auto the link is fine. I’ve tried using another interface device, different cable and the same thing.

The vendor swears is our issue but I really fail to believe that. Could it possibly be something to do with our MTU size, which is 1500 ??
Question by:supportemea
    LVL 8

    Accepted Solution

    Ran into a similar issue recently.  You mention that you've switched cables, but have you tried a different type of cable?  I had originally used a CAT6 straight-through cable connecting my fiber MUX to my Cisco router, and was only getting half duplex.  Did all sorts of testing with my provider, and it turns out the solution was pretty simple:  use a crossover cable instead.  Brought me up on 100Mbps at full duplex.

    Give it a try!
    LVL 15

    Expert Comment

    I agree with Moonie. Is this Verizon? Put a crossover cable in there and fix it 100FDX.
    LVL 7

    Expert Comment

    Autoneg duplex has been a nasty issue for ages.  The general rule is that both ends of a link have to match.
    Provider sets auto: you set auto
    Provider sets FDX: you set FDX
    Provider sets HDX: you set HDX

    Its nothing to do with MTU, and it *should* be nothing to do with cable type (but worth a try i suppose).

    Can you say what device you are connecting to the link, and what other devices you've tested with?

    Can you ask the provider to confirm if the interface should be set to auto/auto or 100/fdx?

    Expert Comment

    I think Unfragmented is absolutely correct.
    verify with Provider
    LVL 2

    Author Comment

    Crossover Cable and forced full/100 worked a treat!

    Thanks a million Moonie!

    interface GigabitEthernet0/1
     speed 100
     duplex full
     no mdix auto

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