Cisco SFP-1G vs. GLC – Key Differences Explained

For some time now, Cisco has been offering new 1G SFPs for fiber and copper connections, namely “SFP-1G-SX” for multimode, “SFP-1G-LH” for singlemode, and “SFP-1G-T-X” with an RJ45 connector.

This can lead to confusion, because one might assume that they work in the same way as the GLC-LH-SMD, GLC-SX-MMD, and GLC-T. However, they are not interchangeable, and you cannot, for example, use an S.8512.02.D as a substitute.

The reason is that these three special Cisco SFPs present 10G to the host on the electrical side, but only 1G on the media side. Cisco describes the SFPs to work in 10G, 10/25G dual rate and 10/25/50G tri-rate ports of Cisco switches and routers, but enabling 1G connections and interoperability with any 1G SX or 1G LX SFP.

Source: https://www.cisco.com/c/en/us/products/collateral/interfaces-modules/gigabit-ethernet-gbic-sfp-modules/datasheet-c78-366584.html

These are SGMII-based transceivers, which in practice means that the SFP-1G-SX is not compatible with native 1G ports, while the GLC-SX-MMD cannot be used in ports which lack native 1G support.

Please keep this in mind when planning your network. As always, feel free to reach out to us if you are unsure which transceiver is right for you.