3750 Error disabled ports from loopback??

Paul,

What's your cabling like? Every time I've seen this, it's been a cabling issue.

Steve

Thanks Steve,

We are using CAT5 cabling. This was never a problem with the old 3548 switches we just removed.

Paul

Paul,

Cheers Steve

Many thanks for that Steve. One last question though... what does it actually mean by loopback?

It means that the switch has detected that it can "see" itself over the cable. I run into this at one of my sites where they use IBM Type I cabling. With the Type I plug, if it's not plugged into something, it loops back the Tx pair onto the Rx pair (it's a 2-pair cable). So, if you plug a RJ45 - Type I lead into your switch, but there's nothing on the end of the Type I plug, the switch errdisables the port.

Cheers Steve

Thanks Steve,

I have now set the detection status for loopbacks to disabled using the command you suggested. Is this setting to be confused with spanning tree? Obviously I still want loops to be detected and blocked on the uplink Gigabit ports using STP.

Thanks again,

Paul

Hi Paul,

What do you have connected to that port? Is it PC or another switch/hub?

If it is another switch, make sure this port is only way to this switch. It's the purpose of Spanningtree protocol - detect loops in the network and disable one link to break the loop.

If you have PC, then you may have a duplicate MAC addresses in your network. It's one of the ways how switch detects loops - if it sees one MAC address on two ports, it thinks that it's possible loop.

Mike