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I need some help understanding a problem we're having at work: We run Altiris/Deployment Solution and have to use auto-negotiate between client systems and our switches (Altiris apparently requires this for imaging, PXE boot and other functions). We have several areas with old wiring (Cat 3 & Cat 5) that have old 10/100 Cisco switches in them - and we can set these systems up to "auto/auto" (auto-negotiate on both the NIC and the switch port), and everything has been working fine. But - our networking crew changed out a couple of old switches for 10/100/1000 Cisco switches, and now - they are claiming that "auto/auto" won't work because the switches can't auto-negotiate the way the old 10/100 switches did - and that if we try to set the new gig switches to auto-negotiate, the switch port starts "port flapping", and shuts the port down. But - if we put the old switch back in - they work using "auto/auto" just fine - no port flapping. The networking crew is telling me that the problem is that we're putting "new switches" on "old wire", and that the old cabling can't/won't support the auto-negotiation with these new switches....???

There's something about this that doesn't make sense to me - can someone explain this to me? Or is our networking crew just doing something wrong in the configuration of these new switches? While will the old switches work "auto/auto", but the new switches won't??

HELP!!....and Thanks!!


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What model switches are in place now? – joeqwerty Oct 21 '12 at 5:26

If the wiring is less than CAT5e and the workstations have GbE NICs in them, you may find they try to negotiate GbE with the switch, only to fail due to the cable being unable to support it, thus causing the port flapping.

You should force the switch to use 100baseTX on the ports connected to a run less than Cat5E to prevent this. It makes sense that you can't do this on the client side if you are reimaging; this is not a limitation of Altiris (which I have used constantly with machines that have auto-negotiation disabled), but rather a limitation of defining the port speed in software (which gets reset to default, of course, during reimaging).

You can do this because these layer 1 details are abstracted out, and have no bearing on the operation of application protocols such as PXE boot.

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