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Can 10Gb Switch Port Link to Gigabit Switch Port?

December 25, 2019

Issue of SFP to SFP+ compatibility has been confusing many network switch users with 10G switches gaining more and more popularity among home and enterprise networks. Will 1G SFP optics work with 10Gb SFP+ ports on a 10Gb switch? Or will 10Gb SFP+ run at 1Gb to link gigabit switches? What if using SFP+ ports on a switch but SFP on the other? Then we’ll ’reveal the mask of SFP to SFP+ compatibility.

What Is SFP Port on Gigabit Switch?

Ethernet switch, known as LAN (Local Area Network) switch, is the most common form of network switch. Fixed-configuration switches are the most used ones with different speeds including Fast Ethernet switch (100 Mbps), Gigabit switch (1000 Mbps), 10Gb switch (10000 Mbps), as well as 25G/40G/100G/400G switches. As the sizes and data rates of Ethernet network switches vary, the switch port types also do. SFP (small form-factor pluggable) port on network switch is a compact, hot-pluggable network interface. Typical speeds were 1 Gbit/s for Ethernet SFPs and up to 4 Gbit/s for Fiber Channel SFP modules. SFP port (electrical port and optical port) enables a gigabit switch to achieve fiber uplink over longer distances or short-range copper uplinks by inserting the corresponding SFP module (fiber SFP or copper SFP).

Figure 1: SFP Port and Uplink SFP+ Port on Gigabit Switch

What Is SFP+ Port on 10Gb Switch?

SFP+ and SFP ports are virtually identical in size and appearance. The primary difference is that SFP+ is an updated version of SFP but supports higher speeds up to 10Gbps. There are mainly two types of 10Gb switch, including 10G fiber switch and 10GBASE-T switch, both of which could have higher-bandwidth uplink ports (25G/40G/100G) to connect with other higher-speed switches in the topology.


Figure 2: SFP+ Port and Uplink QSFP+ Port on 10Gb Switch

Can 1G SFP Optics Run at 10G SFP+ Port?

It may depend greatly on the switch models – sometimes SFP optics are supported in SFP+ ports, and sometimes not. In most situations, 1G SFP transceivers can work with 10G SFP+ ports. SFP+ ports often accept SFP optics but at a reduced speed of 1Gb. And sometimes this port will lock the speed at 1Gb until you reload the switch or do some fancy set of commands. Besides, the SFP+ port usually can never support speed under 1G. That is to say, you can’t plug the 100BASE SFP in the SFP+ port.

There are many vendors providing 10Gb switches such as FS S5860-20SQ switch that can take both a 10G SFP+ transceiver and a 1G SFP in the 10G SFP+ slot, but not at the same time. To make it simple, you can plug 1G SFP into any SFP+ ports of FS S5860-20SQ switch so it can provide a 1G link between S5860-20SQ and the connected devices. If you are unsure about the connectivity, it is suggested that you must consult the vendor to make sure the 10Gb switch port supports dual rate before plugging an SFP transceiver into the SFP+ port on your 10Gb switch.

Figure 3: S5860-20SQ Switch With 1G/10G SFP+ Ports

Can 10G SFP+ Optics Run at 1G SFP Port?

Will 10Gb SFP+ run at 1Gb? The answer is definitely “No”. That’s because you can not down rate a 10G SFP+ transceiver. Once a module is installed, the speed of the port is unchanging. Most SFP+ slots are backward compatible with SFP modules to run at 1G speed. However, the SFP slots cannot support higher speed required by SFP+ modules.


Figure 4: FS 10Gb Switch SFP+ Port Links to Gigabit Switch SFP Port

Can SFP+ Optics Auto-negotiate Down to 1G with Gigabit Switch?

Can 10G SFP+ transceiver module plugged in one switch be connected to a 1G transceiver plugged in another switch and negotiate? It depends.

For Ethernet over copper wiring, auto-negotiation is supported. That means, only the BASE-T SFP transceivers support auto-negotiation as copper SFP modules supporting 10/100/1000 auto-sensing.

For fiber-based transceivers such as fiber SFP and SFP+ optics, auto-negotiation is not supported. As a protocol, auto-negotiation only works when it’s running on both sides of the link. The two devices connected in the link will decide together the best speed and duplex mode. Most SFP and SFP+ transceivers only run at its rated speed as they are manufactured, thus 10Gb SFP+ optics on 10Gb switch can not auto-negotiate down to 1Gb if the other end is gigabit switch.

For example, if a 10Gb SFP+ module is plugged into the 10Gb switch port, it will only run at 10Gb. In this case, if you link it to the gigabit switch port, it will not work. But when plugging a 1Gb SFP module in the 10G SFP+ port, the 10Gb switch will run at 1Gb. If so, you can link it to the Gigabit switch.


For the issue of SFP to SFP+ compatibility, a simple answer is that most SFP+ can take SFP but not vice versa. Thus 10G SFP+ optics on 10Gb switch port is possible to link to 1G gigabit switch port when 1Gb SFP modules are plugged into each port. To make sure the smooth network transmission, you need to consult the switch vendor to ensure the connectors on both ends are the same and no manufacturer compatibility issue exists. If needed, FS is pleased to help you at any time.


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