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SFP Compatibility Guide: SFP SFP+ vs SFP28 SFP+ vs QSFP28 QSFP+



To understand the SFP compatibility issue of SFP SFP+ compatibility, SFP28 SFP+ compatibility, and QSFP28 QSFP+ compatibility, find answers in this post.




The optical transceiver module is a compact, hot-pluggable network interface module widely used in high-speed data communications. It is used for electrical and optical signal conversion between two devices such as network switches and routers. Optical transceivers can be divided into many different types according to different connector types and form factors, such as SFP, SFP+, SFP28, QSFP+, QSFP28, etc. Can different types of transceivers be compatible with each other? For example, can an SFP module work in an SFP+ switch port? Or is an SFP+ backward compatible with an SFP module?


This post is an SFP compatibility guide, illustrating the transceiver compatibility issue among the most popular form factors - SFP SFP+ compatibility, SFP28 SFP+ compatibility, QSFP28 QSFP+ compatibility.


SFP SFP+ Compatibility


SFP and SFP+ compatibility may refer to different issues due to different usage scenarios. Here we clarify SFP vs SFP+ compatibility from three aspects.


Case 1: SFP Module into SFP+ Port

SFP+ is also called SFP plus, the enhanced version of SFP. SFP and SFP+ are identical in appearance, but SFP+ raises the data rate from 1Gbps to 10Gbps. Is it fully functional to plug SFP optics into SFP+ ports? In most cases, SFPs can work in SFP+ ports but at the cost of sacrificing speed to 1Gb/s. Owing to SFP+ is backward compatible with SFP but not vice versa. However, there is no sure say since it depends on SFP models, networking equipment, and vendors. The author suggests you consult your vendors for exact answers.


① Plug a 1000BASE-SX SFP transceiver into the SFP port on a gigabit switch

② Insert a 1000BASE-SX SFP transceiver into the SFP+ ports on a 10G switch

③ Connect the two modules with an OM3 multimode fiber optic cable to achieve 1Gbps data rate connectivity


Solution Product Lists:

1/2. Cisco GLC-SX-MM Compatible 1000BASE-SX SFP Transceiver Module

3. LC UPC Duplex OM3 Multimode Fiber Patch Cable


Case 2: SFP+ Module into SFP Port

What about the other way around? Can the SFP port take the SFP+ module? Seriously? I doubt no one will do this. Given that 10G SFP+ in an SFP port can not run at 10Gbps. So what is the point of a 10G module inserted into an SFP port? It is more economical and worry-free to use the 1G module directly.


Case 3: SFP+ Module and SFP Module Connectivity

Again, how about the SFP+ module and SFP module interconnectivity? Does SFP+ work with SFP? Can it work in the cases where an SFP+ module plugged in a 10Gb switch connects to an SFP module plugged in another gigabit switch? It depends on the types of module and transmission link. Most fiber 10G SFP+ optics can only run at fixed 10G/s, which explains why 10G SFP+ fiber transceivers can not auto-negotiate down to 1Gbps or less to support the SFP module. However, it is feasible in two cases. 


First, the transmission medium between two switches is Ethernet over copper cabling. As we know, the 10GBASE-T SFP+ copper transceiver supports auto-negotiate 10/100/1000Mbps. So both ends of the transmission link can maintain the same speed. For instance, there is a 10GBASE-T SFP+ module on a 10-gigabit switch and a copper SFP on a gigabit SFP switch. If you want to connect the two modules, pick an Ethernet Cat5e cable for connection. 

Solution Product Lists:

1. Cisco SFP-10G-T-S compatible 10GBASE-T SFP+ copper transceiver

2. Cisco GLC-T compatible 1000BASE-T SFP copper transceiver

3. Cat5e/Cat6 Ethernet patch cable


Second, the SFP+ optics is a dual-rate 1G/10G SFP+ fiber module, supporting 1G and 10G Ethernet links over SMF or MMF. Vendors such as QSFPTEK provide this kind of dual-rate module, including dual-rate 1000BASE-SX and 10GBASE-SR SFP+, 1000BASE-LX and 10GBASE-LR SFP+, 10G/25GBASE-SR SFP28. To get a quote, please contact us for the best price and tailored solutions.


QSFPTEK Dual-Rate SFP Price










Note: Click the price or picture, you will direct to the product page.

SFP28 SFP+ Compatibility

The most commonly asked question on SFP28 SFP+ compatibility is - Is SFP28 compatible with SFP+? Generally speaking, the short answer is yes. SFP optics work in SFP+ ports, but not vice versa. Understanding this point, review the relationships between SFP28 vs SFP+. SFP28 (small form-factor pluggable 28) is the enhanced version of SFP+ because it upgrades data rates while inheriting the same package type as SFP+. SFP28 is designed for 25Gb/s data rate transmission, yet it has backward compatibility with SFP+. For example, if plugging an SFP+ module into the switch SFP28 port, the SFP+ module will work well but the max transmission speed will auto-negotiate down to 10Gb/s. 


QSFP28 QSFP+ Compatibility

Now we step into the high-speed era. Is QSFP28 compatible with QSFP+? Through the previous knowledge, you may already have the answer yourself. Let us go over the previous to find the answer. In most situations, SFP optics can be plugged into SFP+ ports while SFP+ optics cannot be plugged into SFP ports. Similarly, QSFP+ optics works in QSFP28 ports but QSFP28 optics cannot work in QSFP+ ports. Let's go back to the reason behind it. The size of the 100G QSFP28 optical module and QSFP+ module is identical. The former also has four parallel data channels, but the transmission rate of each channel has been increased from 10 Gbit/s to 25 Gbit/s, thus reaching a transmission rate of 100Gbps. QSFP28 supports not only full speed 1x 100GbE, but also 4x 10GbE and 4x 25GbE. Therefore it is feasible to plug QSFP+ optics into QSFP28 ports to run at 40Gbps. 



The puzzles of transceiver compatibility often focus on optics-to-device or optics-to-optics interoperability. SFP compatibility with SFP+, SFP28 compatibility with SFP+, and QSFP28 compatibility with QSFP+ are common topics. In brief, the new-gen optical transceiver is backward compatible with the previous version in most situations. In other words, SFP+ ports can take SFPs, it is possible to plug SFP+ into SFP28 ports to run 10G, and QSFP+ optics work fine in QSFP28 ports, but not vice versa. 


No matter what the SFP compatible issue is, it will be easy to handle if you understand the working principle. To avoid errors caused by SFP compatibility issues, remember to ensure the same data rates at both ends of the link and ask your supplier to make sure there will be no exceptions.


Related Article:


Dual-rate 10G/25G SFP28 Transceivers Used In 10G to 25G Upgrades

Cisco SFP Compatibility Matrix - SFP Guide



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