Cisco Optics Part Numbers Decoded: SR, LR, ER, the Numbers, and That -S on the End

Written and maintained by Haink's network infrastructure team · Reconstructed from Cisco transceiver data sheets, 22 August 2026 · authorized-channel, serial-verified

As with switch part numbers, Cisco publishes no glossary for its optics naming. The structure is consistent enough to read once you know the pattern, and the parts that are not documented are worth knowing too — because a supplier confidently explaining what the "H" in SFP-H10GB-CU1M stands for is explaining something Cisco has never defined.

The structure

QSFP-100G-LR4-S

Form factors: GLC- and SFP- for 1G SFP, SFP-…10G for SFP+, SFP-…25G for SFP28, QSFP- for QSFP+ 40G and QSFP28 100G, QDD- for QSFP-DD 400G, CVR- for converters, FET- for fabric extender transceivers.

Reach classes

Cisco does not define what the letters in DR, FR, VR or ERL stand for anywhere in the data sheets — only the reaches. Anyone offering an expansion is guessing.

The number is lanes, not distance

The digit after the reach class is the count of optical lanes or wavelengths, and it determines the connector and the cabling:

• SR4 — four parallel lanes at 850 nm over multimode, MPO connector
• LR4 — four wavelengths around 1310 nm multiplexed onto one duplex single-mode pair, LC connector. QSFP-100G-LR4-S uses 1295, 1300, 1304 and 1309 nm
• SR8 — eight lanes, MPO-16
• No digit — a single lane. QSFP-100G-LR-S and QSFP-100G-DR-S are single-lane 100G
• 4X or 2X in the middle — breakout. QSFP-4X10G-LR-S is 40G broken out as four 10G links; QDD-4X100G-FR-S is 400G as four 100G

This matters practically: SR4 needs MPO trunk cabling, LR4 runs on ordinary duplex LC. Two modules with the same speed and similar names can need completely different cable plant.

Suffixes

Cisco's temperature classes: commercial 0 to 70 °C, extended −5 to 85 °C, industrial −40 to 85 °C.

SFP-10G-SR versus SFP-10G-SR-S

Identical optics — same 850 nm, same multimode reach from 26 to 400 m depending on fibre grade. The documented difference is that the -S does not support FCoE. It is cheaper, and for an Ethernet-only link there is no technical reason to pay for the non-S part. The same logic applies to LR/LR-S, ER/ER-S and ZR/ZR-S.

GLC-T versus GLC-TE versus SFP-GE-T

All three are 1000BASE-T copper SFPs, 100 m over Cat 5, and none of them supports DOM. The difference is temperature rating and qualification:

So the choice between them is environmental, not functional — and in a normal wiring closet the cheapest is the right one.

DAC and AOC cables

The pattern is form factor, speed, type, length: SFP-H10GB-CU1M, QSFP-H40G-AOC10M. CU is passive direct-attach copper, ACU is active copper with signal-regenerating electronics, AOC is an active optical cable with transceivers permanently attached. The trailing number is metres. What the H stands for is not defined in any Cisco data sheet.

The 25G DAC detail worth knowing before you order

On 25G direct-attach copper the FEC requirement changes with cable length, which means the cable choice constrains the switch configuration:

Ordering a 3 m cable where a 2 m would reach turns a plug-in job into a configuration change on both ends — and a mismatch is a link that comes up and drops packets rather than one that fails cleanly.

Reach, by fibre grade

The SR reach figure people quote is almost always the OM4 number. The real distance depends on the fibre in the ground:

A building cabled with OM1 gets 33 m from a module rated at 400 m. That gap is where "the optic must be faulty" tickets come from.

Two more from the data sheet footnotes that catch people out. Minimum cabling distance for SR, LRM, LR and ER modules is 2 m per IEEE 802.3ae — a patch cable shorter than that can overload the receiver. And the long-reach modules need attenuators on short links: ZR requires a 5 dB attenuator below 20 km, and ER requires 15 dB below 5 km, 10 dB between 5 and 25 km, and 5 dB between 25 and 45 km.

Quick reference by speed

Frequently asked questions

What does the -S mean on Cisco optics?

It denotes the S-Class variant. The only difference Cisco documents is that it does not support FCoE — "SFP-10G-SR-S does not support FCoE". The optical specification is identical, and it is cheaper, so for Ethernet-only links it is normally the right part.

What is the difference between SR4 and LR4?

The number is the count of optical lanes. SR4 uses four parallel lanes over multimode fibre with an MPO connector. LR4 multiplexes four wavelengths onto a single duplex single-mode pair with an LC connector. They need different cable plant.

What is the difference between GLC-T and GLC-TE?

Temperature rating only. Both are 1000BASE-T copper SFPs reaching 100 m over Cat 5 with no DOM. GLC-T is commercial 0–70 °C; GLC-TE is extended −5 to 85 °C. SFP-GE-T matches GLC-TE and adds NEBS 3 ESD.

How far does SFP-10G-SR actually reach?

From 26 m to 400 m depending on the fibre. OM1 gives 33 m, OM2 gives 82 m, OM3 gives 300 m and OM4 or OM5 gives 400 m. The 400 m figure people quote assumes the best fibre grade.

Do I need FEC on a 25G DAC cable?

It depends on the length. Cisco specifies no FEC up to 2 m, BASE-R FEC at 2.5 and 3 m, and RS-FEC at 4 and 5 m. The cable length therefore constrains the switch configuration at both ends.

What does the H stand for in SFP-H10GB-CU1M?

Cisco does not define it in any data sheet. The rest of the name is readable — CU is passive copper, the number is the length in metres — but the H is undocumented.

Related

• Cisco optics compatibility — the three checks before you order
• Unsupported transceiver errors — fake, or just incompatible?
• Nexus 9300 refresh — QSFP-DD and 400G breakout
• Reading a Catalyst part number
• Optic modules and transceivers · Cisco stock and lead times · How to choose Cisco

Sources

• Cisco — 10GBASE SFP+ data sheet · 1G SFP · 25G SFP28
• Cisco — 40G QSFP+ data sheet · 100G QSFP28 · 400G QSFP-DD
• Cisco — CWDM SFP data sheet · DWDM SFP+
• Cisco — transceiver data sheet index