GBIC vs SFP vs SFP+ vs XFP vs QSFP: Transceiver Form Factors
GBIC, SFP, SFP+, XFP, QSFP+ and QSFP28 are the transceiver form factors you will meet in a mixed estate, and they are not interchangeable. This covers what each one is, which port takes which module, and how to tell them apart on the bench.
What are the different transceiver form factors?
In rough order of age and speed.
GBIC — the original pluggable optic, large, 1 gigabit. Found on older switches and storage equipment. Largely obsolete but still in service.
SFP — the small form factor replacement for GBIC. 1 gigabit. Much smaller, same job. The most common form factor in older and entry-level equipment.
SFP+ — the same physical size as SFP, 10 gigabit. Fits SFP+ ports; frequently accepts SFP modules at 1 gigabit, but not the other way round.
XFP — an earlier 10 gigabit form factor, larger than SFP+. Found on older 10G equipment. Not interchangeable with SFP+.
QSFP+ — four lanes of 10 gigabit, 40 gigabit total. Larger than SFP+.
QSFP28 — four lanes of 25 gigabit, 100 gigabit total. Same physical size as QSFP+; fits QSFP28 ports and usually accepts QSFP+ modules at 40 gigabit.
Our transceiver compatibility guide covers vendor coding, which is a separate issue from form factor.
Will an SFP fit an SFP+ port?
Usually, at 1 gigabit.
SFP+ ports are physically identical to SFP ports and most accept an SFP module, running the port at 1 gigabit. This is the common way to connect older 1G equipment to a 10G switch.
Two caveats. Not every SFP+ port supports the 1G fallback — some platforms are 10G only. And the reverse never works: an SFP+ module in an SFP port does not run, because the port cannot drive 10 gigabit.
Will an XFP fit an SFP+ port?
No. Different physical size, different electrical interface.
XFP and SFP+ both carry 10 gigabit but are separate form factors. Equipment with XFP ports takes XFP modules only. This catches people replacing an older 10G switch with a newer one and finding their existing optics do not fit.
Will a QSFP+ fit a QSFP28 port?
Usually, at 40 gigabit.
QSFP28 ports are physically the same as QSFP+ and most accept a QSFP+ module, running at 40 gigabit. As with SFP in SFP+, the reverse does not work: a QSFP28 module in a QSFP+ port does not run.
QSFP ports can also be broken out into four SFP+ or SFP28 links using a breakout cable, where the switch supports it. Confirm port configuration support before buying breakout cables.
How do I identify a transceiver I already have?
Four things to look at.
Physical size. GBIC and XFP are noticeably larger than SFP/SFP+. QSFP is wider than SFP+. Once you have seen them side by side it is obvious.
The label. Modules carry the form factor and speed, often with a vendor part number. Our part numbers guide covers reading vendor codes.
The connector on the optical side. LC duplex is most common on SFP and SFP+. MPO/MTP on QSFP parallel optics. SC on older GBICs.
What the switch reports. Most managed switches identify inserted modules by type and vendor in their management interface.
Which form factor should I buy?
You do not choose. The port decides.
Identify the port on both ends of the link, since each end needs a module its own port accepts. Then match speed and wavelength between the two modules, and confirm vendor coding for each device. Our SFP-10G-SR guide covers one common module in detail.
Two practical notes. Legacy form factors are getting expensive as supply thins — GBIC and XFP in particular. Where equipment with those ports is still in service, hold spares. Our spares guide covers this.
And direct attach copper exists for SFP+, QSFP+ and QSFP28 and is cheaper than optics for short runs. It carries the same vendor coding rules. Our fibre guide covers when optics are the right choice instead.
Frequently asked questions
What is the difference between SFP and SFP+?
Same physical size, different speed. SFP is 1 gigabit; SFP+ is 10 gigabit. An SFP module usually works in an SFP+ port at 1 gigabit. An SFP+ module never works in an SFP port.
What is a GBIC and is it still used?
The original pluggable 1 gigabit optic, much larger than SFP. Largely obsolete but still in service on older switches and storage equipment. Supply is thinning and prices are rising; hold spares if you depend on GBIC ports.
Is XFP the same as SFP+?
No. Both carry 10 gigabit but XFP is physically larger with a different electrical interface. XFP ports take XFP modules only. This catches people upgrading older 10G equipment.
Will a QSFP+ module work in a QSFP28 port?
Usually, at 40 gigabit. QSFP28 ports are physically the same as QSFP+ and most accept the older module. The reverse does not work.
Can I split a QSFP port into four SFP+ links?
Where the switch supports breakout configuration, yes, using a breakout cable. Confirm port configuration support before buying the cable, since not every QSFP port can be split.
How do I know which transceiver my switch takes?
The port type is in the switch specification and usually printed near the port. Existing modules can be identified by size, label and what the switch management interface reports.
Send us the switch models at both ends of the link and we will confirm form factor, speed and vendor coding together before you order.
