Which SFP / transceiver fits which Cisco switch?
The uplink type decides everything: 1G vs 10G vs 25G ports take different modules. How to read a switch's uplink and pick the right optic.
NEnetzspec — Optics
Optics desk2026-08-10 · 3 min read
Optics desk2026-08-10 · 3 min read
The #1 transceiver mistake is putting a 10G module in a 1G uplink (or vice versa). The switch's uplink port type decides which module fits.
Step 1 — read the uplink
- 1G SFP ports take 1G modules: GLC-T/GLC-TE (copper), GLC-SX-MMD, GLC-LH-SMD (fiber).
- 10G SFP+ ports take 10G (SFP-10G-SR/LR) and usually 1G too.
- 25G SFP28 ports take 25G and 10G.
- 40G/100G QSFP ports take QSFP modules (or break-out).
Example: the C9200L-24P-4G has 4x 1G SFP uplinks — so a GLC-TE fits, but an SFP-10G-SR does not (that needs the -4X 10G variant).
Step 2 — fiber vs copper & reach
- Copper (RJ-45) for short in-rack runs.
- Multimode (SR) for up to ~300–400 m; single-mode (LR) for up to 10 km.
Step 3 — genuine coded optics
Cisco switches read the module's EEPROM. Use genuine, correctly-coded optics to avoid errors and support issues. Every part page lists verified compatibility — check before you buy.