How to read a Cisco transceiver part number

A Cisco optics part number is not arbitrary. Read left to right and it tells you the form factor, the speed, the optical standard and, in the suffix, a set of conditions most people ignore until something does not work.

The prefix is the form factor

• GLC- — 1G SFP. The older naming, still in use: GLC-SX-MMD, GLC-LH-SMD, GLC-T.
• SFP-1G-, SFP-10G-, SFP-25G- — the modern pattern, with the speed stated directly.
• QSFP-40G-, QSFP-100G- — QSFP+ and QSFP28.
• QDD- — QSFP-DD, used for 400G and 800G.
• OSFP- — OSFP, the other 800G cage.
• FET- — Fabric Extender Transceiver, locked to fabric extender links rather than general use.
• DS- — storage, meaning Fibre Channel rather than Ethernet.

The middle is the optical standard

SR, LR, ER, ZR, BX, CWDM, DWDM, and the parallel variants SR4, LR4, DR4, SR8. This is the part that tells you the fibre and the reach, and it is covered in our guide to choosing a transceiver.

A number after the standard is a lane count, not a speed. The 4 in QSFP-100G-SR4 means four lanes of 25G, which is why it needs an MPO trunk rather than a duplex LC patch cord.

The suffixes are where it gets interesting

-S marks Cisco's S-class optic. These are single-rate and Ethernet-only, where the equivalent C-class part is multi-rate and also handles OTN and WAN-PHY. S-class is commercial temperature only and does not support FCoE. For a campus access or aggregation link none of that matters; for a service-provider platform expecting OTN it very much does. That is the real difference between SFP-10G-LR and SFP-10G-LR-S, and it is not simply a cheaper version of the same thing.

-I is industrial temperature, roughly −40°C to 85°C. -X is extended temperature, between commercial and industrial. -RGD is ruggedised, for the industrial switch lines.

-D on the older 1G parts indicates digital optical monitoring: GLC-SX-MMD is the DOM-capable version of GLC-SX-MM. If you rely on reading transmit and receive power off the switch, you want the D.

-U and -D on BX parts mean upstream and downstream, which is a wavelength pairing rather than a feature — more on that in the BiDi guide.

A trailing =, as in SFP-10G-SR-S=, is Cisco's spare or standalone orderable number. It is the same module as the one without it; the equals sign only signals that it is ordered on its own rather than configured into a system. You never need to match it when buying compatible optics.

Cables follow their own pattern

CU means passive copper twinax and AOC means active optical cable, with the length appended: SFP-H10GB-CU3M is a 3m 10G DAC, SFP-10G-AOC5M is a 5m 10G AOC. A leading multiplier such as QSFP-4X10G- or QDD-2X100- marks a breakout, splitting one port into several slower ones.

Why our part numbers end in -OO

Every part we sell carries the OEM part number with -OO appended, so SFP-10G-SR-OO is our module coded for a Cisco SFP-10G-SR. It keeps our catalogue searchable by the number you already have in front of you while making clear the part is ours rather than Cisco's.

Where a second vendor uses an identical part number — Arista and Cisco both ship an SFP-10G-SR, for instance — we add a letter to keep them distinct: SFP-10G-SR-A-OO is the Arista-coded one. Search either number and you will land on the right part.