Aug
9
Written by:
Stephen Frost
9/08/2010 1:06 PM
Just purchased six (6) new Cisco SG100-24 unmanaged switches which I was planning to use in our switch rack at work and uplink into our HP Procurve switching backbone ... but when I connected port 24 up ... nada ... nothing ... didn't light up ... no traffic flowing. In the past we had used the Cisco SR2024 switches, which uplinked through port 24 just fine. However the SR2024 had reached end of life and my supplier was telling me that the SG100-24 was its replacement.
So I'm thinking to myself ... does the SG100-24 only provide uplink through its miniGBIC ports and NOT through the port 12 and port 24 gigabit ports? Should I be buying a different model of switch? I figured its not a physical cabling issue, because I could plug a laptop into the same patch panel port as I am trying to use for the SG100-24's uplink and it connected me up just fine; plus I plugged an old Netgear 100Mbit/sec switch into that same physical port and it uplinked straight away.
So I rang Cisco support. They were non-plussed, but since their documentation for the SG100-24 doesn't explicitly say that it supports uplink, they said "Yeah, well I guess it doesn't do that; that's odd". What to do?
I bought a new gigabit Netgear unmanaged switch, as its documentation explicitly said that it supports auto-sensing uplink negotiation on all ports ... plugged it all in and ... it FAILED. Huh?
I then routed a link from our core switch down through a different physical cabling path 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 will not auto-uplink if there's anything dodgy going on at all 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. You need to test a whole other physical path if you want to be sure. In our case, it turned out that pins 4 and 5 on the patch panel were not wired in, which allowed 100Mbit/sec switches to work just fine, but prevented the 1Gbit/sec switches from working.
Apologies to Cisco for my ever doubting the quality of their product!