The Cisco GBIC is a hot-swappable input/output device that plugs into a Gigabit Ethernet port or slot, linking the port with the network.
Cisco GBICs can be interchanged on a wide variety of Cisco products and can be intermixed in combinations of 1000BASE-T, 1000BASE-SX, 1000BASE-LX/LH, 1000BASE-ZX, or 1000BASE-CWDM interfaces on a port-by-port basis.
You cannot configure speed or duplex mode on GBIC ports.
But for certain types of GBICs (for example, 1000BASE-SX, -LX, or -ZX GBICs), you can configure the speed to not negotiate (nonegotiate) if they are connected to a device that does not support auto-negotiation.
The GBIC-module ports support only 1000 Mbps.
The speed values of 10 Mbps and 100 Mbps are not supported.
You cannot hardcode 100 MB on a 1000Base GBIC and it will always be 1000 MB full duplex whereas the 100BASE-FX will be 100 MB full duplex.
For more information refer to:
Cisco Gigabit Interface Converter (GBIC)
The Cisco SFP Gigabit Interface Converter is a hot-swappable input/output device that plugs into a Gigabit Ethernet port or slot.
SFPs can be used and interchanged on a wide variety of Cisco products and can be intermixed in combinations of 1000BASE-SX, 1000BASE-LX/LH, 1000BASE-ZX, or 1000BASE-BX10-D/U on a port-by-port basis.
On the other hand, SFP modules are available in the two speeds of 100 Mbps and 1000 Mbps.
You can connect a 100BASE-FX SFP FastEthernet interface converter on Gigabit SFP ports in Catalyst 3750, 3560 and 2970 Series Switches.
For more information refer to:
Cisco SFP Optics For Gigabit Ethernet Applications
and
Cisco 100BASE-X SFP Module for Fast Ethernet SFP Ports
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