Optical Transceivers

What an SFP transceiver is

An SFP transceiver is the small pluggable module that gives a switch, router, server or HBA port its optical or copper link. Cisco defines the SFP as a hot-swappable input/output device that plugs into a Gigabit Ethernet port or slot, and SFP+, SFP28, QSFP+ and QSFP28 modules extend the same pluggable idea to higher speeds:

Which optic reaches how far

An optic's standard sets its reach and the installed fiber decides where a link lands; the ratings below come from Cisco's data sheets and, for XFP and CFP, Juniper's EX3200 data sheet and 100G optics guide.

SFP, SFP+ and SFP28 in the same port

The port's rating decides which modules it runs, and faster ports often step down: Cisco rates its two-port Catalyst 9300 network module for 25G, 10G and 1G. Slower ports do not step up, as the question below explains.

Single-fiber BiDi optics

A BiDi optic sends and receives over one strand of fiber on two wavelengths, so it is always bought as a matched pair of opposite modules; the wavelengths and reach are in the question below.

How to choose an optic

1. Match the port's form factor: SFP, SFP+, SFP28, QSFP+ or QSFP28.
2. Pick the standard for the distance and fiber in place, using the reach table above.
3. Match the connector: duplex LC, MPO-12, or a single-strand BiDi pair.
4. Match the coding to the switch or HBA it goes into.

OEM optics and Enterasource coded-compatible optics

An OEM optic carries the switch maker's own part number and coding; an Enterasource -ESI optic is built to the standard in its listing and coded for the platform it names, with Enterasource as the manufacturer of record. Coding matters because switches check it: Cisco's Catalyst configuration guide has the switch verify the serial number, vendor name, vendor ID, security code and CRC in the module's EEPROM and error-disable the interface if any is invalid.

Fibre Channel optics for SAN switches and HBAs

Fibre Channel optics are sold by FC speed, not Ethernet speed: 850 nm shortwave SFP+ modules cover 2GFC to 32GFC links over multimode fiber, 1310 nm longwave modules cover single-mode runs, and each is coded for the HBA or SAN switch maker it serves. Shortwave reach on OM3 falls from 150 m at 8G to 70 m at 32G. The cards these optics plug into are on Fibre Channel HBAs and the wider host bus adapters page.

Copper, uplink modules and switches

Inside a rack, one passive direct-attach cable replaces two optics and a patch cord: see Direct-Attach Cables. Juniper EX uplink modules are on Switch Expansion Modules, complete switches under Cisco, Juniper and Dell Networking, and GPU cluster fabrics in InfiniBand vs Ethernet.

Optical transceiver questions

Are compatible optical transceivers as reliable as OEM?

A compatible SFP or QSFP transceiver can match the OEM part in service when it is built to the same standard, such as 10GBASE-SR, is coded for the switch it goes into, and was tested before it shipped. Coding matters as much as the optics: switches such as Cisco's read the vendor data in the optic's EEPROM and can error-disable a port that fails the check. Enterasource -ESI optics are each coded for one platform, so match the coding to your switch; every optic we ship is tested in-house.

Are SFP and SFP+ modules interchangeable?

Only downward, and only where the port is rated for it. Many 10G SFP+ ports also run 1G SFP optics, as Cisco's Catalyst 9300 eight-port module and Juniper's EX4300 uplink module do, but an SFP+ module will not run in a port built for 1G only; Cisco states its Catalyst 3750-X 1G network module does not support SFP+. Check the port's data sheet first.

What is a BiDi (single-fiber) SFP?

A BiDi SFP transmits and receives on one fiber strand by using different wavelengths in each direction, so it is installed as a matched pair. Cisco's 1000BASE-BX10-D sends at 1490 nm and receives at 1310 nm, the 1000BASE-BX10-U does the opposite, a D module always connects to a U module, and the link reaches up to 10 km over single-mode fiber.