FURTHER TESTING: I tried an old 100Mbit/sec Netgear switch on the same port and it worked fine. Bought a new gigabit Netgear switch, as its documentation explicitly said that it supports auto-sensing uplink negotiation on all ports ... and it FAILED. Huh? I then routed a link from our core switch down to a spare patch port (#5 instead of #1) and it WORKED with both the Netgear and the Cisco gigabit switches. CONCLUSION: There is nothing wrong with the Cisco SG100-24 and it WILL provide uplink on the copper gigabit ports ... BUT ... it (and other similar switches) are sensitive to very minor line faults and may not auto-uplink if there's anything dodgy going on with the physical cabling. Simply plugging in another old switch or plugging a laptop directly into the patch panel ports may not be an adequate test of whether there is a line fault in the physical cabling. Apologies to Cisco for doubting the quality of their product!
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