Alright folks, can anyone provide insight on 1G SFP (optical, SM or MM don't care) that will work? I have tried what I have laying around, and no joy. Seems like the port is forced to 10G, but if I do [Config->Interface 0/2-> Speed ?] it shows 10 or 100M, and if i try either of those, or 1000 it errors with invalid physical mode for this port or invalid input.
Gigabit Ethernet on a SFP+ port requires hardware support in the switch and a SFP that the switch recognizes as compatible. This is a lot harder than it seems, for a number of reasons.
Think of a fiber SFP or SFP+ as a light-to-electricity converter. There is no need for "smarts" inside - just a little EEPROM that tells the switch what the characteristics of the SFP/SFP+ are. Various monitoring functions (transmit / receive optical signal level, temperature, etc.) are optional.
1000Base-T SFPs are a special case - multi-speed ones actually do the speed conversion inside the SFP and look like a vanilla Gigabit port to the switch.
The same problem can show up when you try to do 100Mbit on SFP. Most 100Mbit SFPs are dumb, don't do speed conversion, and need multispeed support in the switch. There are some that do speed conversion, but they're pretty rare. I've never seen an optical GigE/10GbE speed-converting SFP. There's currently no equivalent to the 1000Base-T SFP for 10GbE because any current design would exceed the allowable power available at the SFP+ jack.
If a switch has combo SFP+ / RJ45 ports, those are normally the ones most likely to work with a GigE SFP, since the switch already has to be able to handle multiple speeds on the copper side of things.
SFP / SFP+ are optimized for low price ("low" being a relative term if you're buying genuine Cisco parts). The XENPAK optic, which was used on early designs (normally on a GigE switch that offered one or two "10 Gigabit ready" ports) was much more complicated - the interface on the switch side is pretty close to a dumb parallel port - all of the timing, serialization, and encoding is done in the XENPAK itself. That made the switch design cheap, but the XENPAKs were incredibly expensive, ran hot, and were generally a pain to deal with. They attached to the switch with a pair of thumbscrews, and the electrical connection was a bit "twitchy" - Cisco issued
an advisory that "the switch may begin to smoke" when a XENPAK is inserted and suggested powering off the switch first. X2 was a slightly newer design with the same electrical interface but a smaller physical size. It had an odd design where the way to properly remove the X2 from the switch was to unplug the fiber cable and then tug on the connector, which was spring-loaded and would cause the X2 to release from the switch. Fortunately things became a lot more sensible when SFP+ became the normal module type. Since the "smarts" are moved into the switch, this means that the switch has to be willing to support other speeds besides 10GbE for any chance of an SFP to work.