I was wondering if you can connect a Cat 3550 GBIC port(using ws-g5483) to a CAT 3750 10/100/1000 port as a trunk port. I have tried this setup, but it seems that there may be a speed/duplex issue. I never get a link light between the 3550 GBIC and the 3750, but do get connectivity between the same 3550 GBIC and a 2950 10/100/1000 port. Both the 3550 and the 3750 are set to auto negotiate the port speed.
"You can configure interface speed on Fast Ethernet (10/100-Mbps) and Gigabit Ethernet (10/100/1000-Mbps) interfaces; you cannot configure speed on Gigabit Interface Converter (GBIC) interfaces. You can configure duplex mode on any Fast Ethernet or Gigabit Ethernet interfaces that are not set to autonegotiate; you cannot configure duplex mode on GBIC interfaces.
This still does not explain why the GBIC, which runs at 1000 MB by default (auto-negotiation) does not link up with a 10/100/1000 ethernet port which is set to aut-negotiate. Does the GBIC have to communicate with another GBIC?
You might try seeing what flow-control is set on both ends. To get a cat5000 supe with 5484 GBICs to work with a Dell switch with 5484 GBICs, and a 2950T (UTP 10/100/1000) to work with the Dell with a cisco 5483 1000BaseT gbic, I ended up having to play with these until the link would work.
e.g. try on both ends
flowcontrol receive off
flowcontrol send off
Also (you probably have checked this, but in case you haven't - and if this works with the 2950 I can't imagine why it wouldn't work with the 3550) verify you have all four pairs in your crossover cable correct -
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