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Key takeaways
- MSA compliance means a transceiver follows the industry form-factor and EEPROM specifications, so it fits and works in any port of that type.
- Vendor coding writes a specific vendor identity into the optic's EEPROM so a switch that checks identity accepts it.
- Some switches accept any MSA optic, some log a warning, and some disable the port until a service command allows unsupported transceivers.
- The optical standard (SR, LR, ER) and the fiber type must match at both ends; the vendor coding only needs to match the host switch.
- Quote with the switch model and software, port type, speed, distance, fiber type and the far-end device.
What does MSA-compliant mean?
A multi-source agreement (MSA) is a specification several manufacturers agree to build against so their modules are interchangeable. The SFP, SFP+, SFP28, QSFP+ and QSFP28 form factors are each defined by an MSA published through the SFF Committee, which fixes the mechanical size, electrical connector, power limits and identification memory layout.
An MSA-compliant transceiver therefore fits any port of that form factor and speaks the electrical signals the host expects; on a listing it usually means a generic optic carrying its manufacturer's own name. The optical side is separate: what comes out of the fiber connector is defined by IEEE 802.3 (for example 10GBASE-SR or 100GBASE-LR4), and any two optics that implement the same clause will talk to each other regardless of who made them.
What does vendor coding do?
Every SFP-family module carries a small EEPROM (defined in SFF-8472 for SFP, SFP+ and SFP28, and SFF-8636 for QSFP+ and QSFP28) that stores the vendor name, part number, serial number, wavelength and reach, and on most modules live diagnostics (digital optical monitoring, DOM). The switch reads this memory when the module is inserted.
Vendor coding, also called compatibility programming, writes the fields a particular switch vendor expects: the vendor name, the vendor's own part number, and on some platforms a check value in reserved bytes. A "Cisco-coded" optic is a third-party module written this way; the optics and electronics are unchanged.
Why does a Cisco switch reject or warn on an uncoded optic?
Many Cisco IOS and IOS XE platforms check the EEPROM identity when an optic is inserted. If it does not match a Cisco-approved identity, most of these platforms keep the port down and log the transceiver as unsupported. A hidden service command (the unsupported-transceiver service command) changes this to a warning so the port comes up. Nexus switches running NX-OS vary by model and release: some bring the port up and mark the transceiver as unsupported, others keep it down.
Across the industry the behavior class is the same three options: accept silently, accept with a warning, or disable the port. Juniper, Arista, Dell and HPE Aruba switches land in different places, and behavior can change between software releases, so the software version belongs in a quote. Coding makes the port come up; it does not make the optic vendor-supported.
DAC, AOC or optics: which should I use for each distance?
A direct attach copper cable (DAC, or twinax) has the connector modules permanently attached to a copper cable. Passive DACs need no power and suit links inside a rack; the SFP+ specification (SFF-8431) defines passive copper up to 7 m, IEEE 25GBASE-CR-S defines a 3 m passive class and 25GBASE-CR a 5 m class, and 100GBASE-CR4 defines a 5 m class. Active DACs reach somewhat further.
An active optical cable (AOC) has transceivers permanently attached to a fiber cable. It runs to tens of meters, but the length is fixed and a damaged cable means replacing both ends. Separate optics with a patch cord are the flexible option: you can change fiber length, run through patch panels, and mix vendors at each end as long as both optics implement the same 802.3 standard.
Which form factor maps to which speed?
The form factor tells you the port's lane count and top speed per lane. Most ports also accept the previous generation of the same form factor at the lower speed (check the switch documentation, since some ports refuse a slower module), but the reverse never works: a 10G optic in an SFP port has no 10G host behind it.
| Form factor | Lanes | Top speed | Common standards | Usually also accepts |
|---|---|---|---|---|
| SFP | 1 | 1 GbE | 1000BASE-SX, 1000BASE-LX | 100 Mb/s on some ports |
| SFP+ | 1 | 10 GbE | 10GBASE-SR, LR, ER | 1 GbE SFP |
| SFP28 | 1 | 25 GbE | 25GBASE-SR, LR | 10 GbE SFP+ |
| QSFP+ | 4 | 40 GbE | 40GBASE-SR4, LR4 | Breakout to 4 x 10 GbE |
| QSFP28 | 4 | 100 GbE | 100GBASE-SR4, LR4, CWDM4 | 40 GbE QSFP+, breakout to 4 x 25 GbE |
Breakout is a switch feature, not just a cable feature. A QSFP28 port splits into four SFP28 links only where the switch software supports it on that port, and the port usually has to be configured for breakout before the four links appear. Check the switch documentation for which ports allow it, then order the breakout cable or the MPO harness that matches.
Single-mode or multi-mode, and which reach class do I need?
Multi-mode fiber (MMF) has a 50 micron or 62.5 micron core and is used with 850 nm short-reach (SR) optics. OM3 and OM4 (usually aqua jackets) are the current grades for 10G and above. Single-mode fiber (SMF, OS1 or OS2, usually yellow) has a 9 micron core and is used with 1310 nm long-reach (LR) and 1550 nm extended-reach (ER) optics over kilometers.
| Standard | Fiber | Connector | Reach (IEEE 802.3) |
|---|---|---|---|
| 1000BASE-SX | MMF, 850 nm | LC duplex | 550 m on OM2 or better |
| 1000BASE-LX | SMF, 1310 nm | LC duplex | 5 km (vendor LX/LH parts commonly rated 10 km) |
| 10GBASE-SR | MMF, 850 nm | LC duplex | 300 m OM3, 400 m OM4 |
| 10GBASE-LR | SMF, 1310 nm | LC duplex | 10 km |
| 10GBASE-ER | SMF, 1550 nm | LC duplex | 40 km |
| 25GBASE-SR | MMF, 850 nm | LC duplex | 70 m OM3, 100 m OM4 |
| 40GBASE-SR4 | MMF, 850 nm | MPO-12 | 100 m OM3, 150 m OM4 |
| 100GBASE-SR4 | MMF, 850 nm | MPO-12 | 70 m OM3, 100 m OM4 |
| 40GBASE-LR4 and 100GBASE-LR4 | SMF, 1310 nm band | LC duplex | 10 km |
The reach class must match at both ends and match the fiber. An SR optic on single-mode fiber will not link, and an LR optic over multi-mode is outside the standard (10GBASE-LRM exists for legacy multi-mode at 10G). An ER optic on a very short link can overload the receiver, so check its receive power limits and add an attenuator if needed.
How do I match an optic to my switch and to the far end?
First, the host: the port's form factor and the switch vendor's identity check, which decides whether you need a vendor-coded module or a generic MSA one. Second, the standard: both ends must implement the same 802.3 variant, so an SR on one side needs an SR on the other, even when each optic is coded for a different host.
Third, the fiber: the connector (LC duplex for most SFP-family and LR4 optics, MPO-12 for SR4 parallel optics), the grade (OM3, OM4 or OS2) and the length. Bidirectional (BiDi) optics use a single fiber with two wavelengths and must be bought as a matched pair. For a carrier or colocation cross-connect, get the far-end optic's standard and wavelength in writing. The switch inventory (show inventory on Cisco IOS) reports the installed optic's type and part number; see the part number guide.
What should I send in a quote?
Send the switch make and model and its software version, the port type (SFP+, SFP28, QSFP28), the speed you need, the link distance, the fiber type and connector, and the device at the far end. If you are replacing an existing module, include its part number from the switch inventory. Add DAC or AOC lengths if you want cables, and the quantity.
Quotes are answered weekdays 8:00 am to 5:00 pm PST. Browse transceivers and network switches for part numbers to include. The condition shown on a listing is the condition you receive; warranty terms are on the warranty page.
Frequently asked questions
Will a third-party optic damage my switch?
No. An MSA-compliant module draws power within the limits the form factor specifies and uses the same electrical interface as the vendor's own module. The risks are software ones: a port that stays down until an unsupported-transceiver setting is applied, or a support desk that asks for the vendor's optic before troubleshooting.
Can I mix a Cisco-coded optic with an HPE-coded optic on the same link?
Yes. The coding only matters to the switch the module is plugged into. As long as both modules implement the same standard (both 10GBASE-LR, for example) and the fiber matches, the light on the fiber is identical and the link comes up.
Do I need DOM or DDM support?
Digital optical monitoring (DOM, also called DDM) reports temperature, supply voltage and transmit and receive power from the module to the switch. It is defined in SFF-8472, is optional on 1G SFPs and present on most 10G and faster modules. Ask for it if you diagnose links by optical power.
Can a QSFP28 port run at 40G or as four 25G ports?
Usually. Most QSFP28 ports accept a QSFP+ 40G module, and most switches allow a QSFP28 port to be split into four 25G lanes with a breakout DAC or a parallel optic and an MPO-to-LC fan-out. Breakout is configured per port and limited to certain ports on some models.