What is SFP Port? Everything You Need to Know

Initial Published: December 2, 2022

An SFP port is a physically small slot in a networking device that accepts an SFP module insert. Most modern networking devices, such as Ethernet switches, servers, routers, network interface cards, and fiber media converters, generally have two or more built-in SFP ports. You may connect different switches via SFP modules and corresponding cables to the equipped port, which helps you achieve greater bandwidth and higher network throughput.

In this guide, we’ll cover the following:

• What is an SFP port?
• Types of SFP port
• Why is the SFP port important?
• SFP vs. SFP+ vs. XFP vs. QSFP28 port, what is the difference?
• RJ45 port vs SFP port
• SFP slot vs SFP port
• FAQ

What is an SFP port? 

The SFP port also refers to a Small Form-factor Pluggable port. It is a compact mechanical slot that accepts an SFP module insert for high-speed data transmission and telecommunication applications. When equipped with one or multiple SFP ports, the networking device can use different SFP modules and connect with fiber-optic or copper cables for high-speed data transmission.

Adhering to industry standards like INF-8074i is crucial. It ensures that the networking manufacturer or supplier uses standardized SFP port hardware, enabling all SFP ports to connect seamlessly with others over a corresponding SFP module. This adherence to standards is a key factor in maintaining the integrity and efficiency of the network.

The SFP port is generally used in many networking hardware devices, such as high-speed switches, routers, servers, network interface cards (NICs), fiber media converters, fiber modems, and firewalls.

What types of SFP ports are there? 

Based on the different functions, we can divide them into two types.

SFP combo port 

It is a compound physical opening with the same switch fabric and port number as the corresponding Ethernet port. In other words, it functions the same as another physical port (primarily as a 1000BASE-T RJ45 port). Since those two ports were compounded, we can not use them simultaneously. 

For example, if the SFP combo port is activated, the related RJ45 port is automatically disabled. Because of this principle, we called those ports combo ports. 

Now, let us look at the real combo port on an Ethernet switch.

SFP uplink port

Before discussing this word, we need to know the definition of uplink port. Lifewire explains it like this:

An uplink in computer networking refers to a wired or wireless connection from a ​local area network (LAN) to a wide area network (WAN). An uplink port on a home router is a special kind of port used to connect to a broadband modem (which is a LAN), and ultimately to the internet (which is a WAN).

Now, let’s turn back to discuss the SFP uplink port. 

Also called an SFP uplink port, this port usually connects with the downlink port of higher-speed switches. In this scenario, it acts as the lower-tier network, while another connected device serves as the higher network layer. 

For example, we could connect the uplink port of the Lan switch to the downlink port of the higher-speed WAN switch. Of course, remember they must go via the transceiver module and fiber patch cable. 

You should NOT try to connect two uplink ports to avoid any possible error. Because it will cause a failed link, remember to carefully check the port type before merging with other devices. 

However, we can classify them as different types based on the speed supported.

• Fast Ethernet Port: also referred to as FE port, supports 155Mbps or 100Mbps SFP module; Only some older switches or routers may have this port
• 1G Port: also referred to as gigabit port, supports 1.25G or 1G SFP module; it is the most common transceiver type in the Ethernet switch and router
• 2G Port: support 2G or 2.5G SFP module. It is an unpopular type, mainly for the 2G FC or SDH/SONET devices
• 4G Port: support 4G SFP module. It is usually used in fiber channel SAN switches or servers.
• 8G Port:  support 8G SFP+ module. Like a 4G port, it is commonly found in SAN switches or servers.
• 10G Port: in most cases, also called 10G SFP+ port, it is an enhanced port that supports higher speed. It is suitable for a 10G SFP+ transceiver, providing 10x bandwidth than the regular SFP module.
• Multi-rate port: Unlike the fixed data rate port, this port supports multi-rate SFP modules. Some 10G Ethernet switches from the top brand feature this port, allowing the network administrator to use multiple-speed transceivers in the same ports. It helps to build a flexible and scalable network.

Why is the SFP port important? 

Nearly all high-speed network switches will only work with fiber ports because only fiber can provide the maximum bandwidth over a long distance. Though copper cables still support high-speed transmission, they are thicker, more expensive, dangerous and suitable only for short lengths.

The fiber port is an essential part of modern Ethernet switches. It acts as an important bridge to connect the transceiver and switches and transmits the signal hundreds of kilometers over the fiber cable. 

Now, let’s turn to the reason for its importance.

• First, since the SFP form factor is the most popular and thriving in the transceiver industry, the SFP form is the most reasonable and cost-effective choice. 
• Second, an SFP is smaller than a GBIC port. Hence, we sometimes refer to it as a mini-GBIC port. This helps double the port density in the same switch space. 
• Third, it is hot-pluggable. The network administrator can quickly replace the appropriate SFP module without shutting the switches, making it perfect for expanding or modifying existing networks without completely changing the cable infrastructure.
• Finally, it is cost-effective. Because of the popularity of the SFP form factor, there are many vendors and choices on the market. Hence, switch manufacturers can easily find a reliable supplier at low prices. Those costs finally react to the switch device pricing, expanding the networking market.

SFP port vs. SFP+ port vs. XFP port vs. SFP28 port vs. QSFP28 port, what is the difference? 

If you are a new man to the networking industry, you may also hear about other related words, such as SFP+ port, XFP port, SFP28 port, and QSFP28 port. 

Now, let’s take a simple look at those words.

SFP port is the most common way to call. However, we may also refer to the SFP high-speed port as an SFP+ port, such as 8G, 10G, and 16G data rates.

The SFP28 port supports a 25Gbps data rate but has the same appearance and dimensions as the SFP port. Sometimes, it is back-compatible with an SFP+ port and supports 10Gbps; That depends on the switch manufacturer setting.

XFP port is a physical slot that accepts XFP module plug-ins. It is only for 8G and 10G XFP transceivers but doesn’t support other speeds.

QSFP28 port is primarily for a much higher speed of 100G. Unlike the SFP port, it supports a higher-speed transceiver and features a bigger size and more pins on the connector. 

In other words, the SFP, SFP+, and SFP28 ports are the same size and refer to the same thing except for the support speed. The QSFP28 port is of different types and is suitable for 100G data center switches. 

The table below lists the comparisons between them.

Comparison	RJ45 Port	SFP Port	SFP+ Port	SFP28 Port	XFP Port	QSFP28 Port
Reach	max 100m	max 180km	max 100km	max 80km	max 100km	max 80km
Data Rate	1000M, 2.5G, 5G, 10G	155M, 622M, 1G, 2G, 4G	8G, 10G, 16G	25G	8G, 10G	100G, 112G
Power Consumption	Medium	Lowest	Low	Low	Medium	High
Price	Low	Lowest	Medium	Medium	Medium	High
Size	Small	Small	Small	Small	A bit Bigger	A bit Bigger
Application	Access Switches	Access Switches	Campus Switches	Campus Switches, 5G Fronthaul Network	Campus Switches	Data center switch
Media Type	Only Copper	Fiber or Copper	Fiber or Copper	Fiber or Copper	Fiber or Copper	Fiber or Copper

SFP port vs. RJ45 port

In the real world, some network switches have both RJ45 ports and SFP ports with the same speed. Since they have the same functions, what are the points of the SFP port? What is their actual difference?

RJ45 port only supports copper network cable, providing minimal link distance. The max length of 1G rate over Cat5 cable is around 100 meters. That is not enough in the switch connectivity for the longer link. However, you may achieve tens of kilometers or even 160~180km over single mode fiber. That is the actual performance difference.

Besides the different supported distances, SFP also avoids electrical interference and surge isolation, lower power consumption, and lower total cost.

SFP Slot vs SFP Port

SFP Port is the most commonly used name, but some vendors or users also call it SFP Slot. In most cases, the two terms mean the same thing, so we can usually use them interchangeably.

In some cases, however, an SFP Slot refers to the physical socket or opening on a network device (such as a switch or router) inserted into an SFP module.
On the other hand, an SFP Port is more focused on emphasizing its function as a connection point for data transmission. When an SFP module is inserted into an SFP slot, the slot becomes an active port facilitating network connectivity.

FAQ 

1. What is the maximum link distance between two SFP ports? 

It depends on the SFP module and fiber cable. Different optical modules and fiber optic cables determine the maximum transmission distance.

Take an SFP 1G port as an example. It usually supports the copper module, fiber module, and DAC cable.

• If you use a 1000BASE-T copper SFP module, the max distance reaches 100m over the cat5e cable.
• If you use a fiber SFP module, the maximum distance over single-mode OS2 fiber cable is 180 km, or 550m over multimode OM2 fiber.
• If you use an SFP DAC cable, the max length only supports around 10m.

2. What is the mainstream speed for SFP ports?

The most common speeds are 1Gbps and 10Gbps. However, the answer is typically applied to the usual enterprise network, and we should say 4G, 8G, or 16G SFP for the storage networks. In some SONET/SDH applications, the speed may be 155Mbps, 622Mbps, 2.5Gbps or 3Gbps.

3. Can you aggregate multiple SFP ports?

Of course, you can. Link aggregation can provide more bandwidth, redundancy, and load-balancing benefits. It ensures that one link can immediately switch to a second available link when it fails. So, it is critical for enterprise networks where performance and security are more important.

Sidenote: Make sure you have configured both switches for link aggregation before connecting these ports. Otherwise, it will cause network loops.

4. Can you connect SFP ports on switches from different brands?

You can usually connect them with different brand switches. However, in some cases, you may have failed to connect them. 

However, it would be best if you took care of the below tips.

• Use the SFP module with the same wavelength on the two slots. However, choose the opposite wavelength for the BiDi transceiver module for two slots. The wrong wavelength will cause failed connectivity. For example, when you use 1310nm-TX/1550nm-RX on side A, you should connect them with 1550nm-TX/1310nm-RX on side B.
• Check the switch and SFP module compatibility prior. Some large brands like Cisco locked their SFP slots from generic SFP transceivers. Therefore, you should choose an original transceiver. However, you may also order third-party compatible transceivers because they are usually budget-friendly and help save a lot of money.
• Ensure to use correct and quality fiber cable. A wrong fiber cable may shorten the link distance and even fail the link in some wholes. Remember the SMF SFP transceiver only supports single mode fiber, while the MMF SFP transceiver only supports multimode fiber (to achieve the longer distance, use OM3 fiber cable instead of OM2 fiber cable)

4. How Many SFP Ports Does a Switch Have?

The number of SFP ports on a switch may vary depending on its type. For example, a cheap SOHO switch may only have an RJ45 port but no SFP port.

However, a typical enterprise switch for large networks may have 48 SFP fiber ports and one console port. It is equipped with as many ports as possible to improve density and throughput.

5. What is an SPF port? 

Suppose you are a “new man” in the networking industry. SPF port is the typing error of it. Because they are unfamiliar with this word, some guys may mistype it and call it SPF port. In fact, they are the same thing. Similarly, some guys may call SFP+ the SPF+ port, so remember they are the same thing.

6. Which device has SFP ports?

A: Various networking equipment must be transmitted over fiber with SFP ports. The device includes an Ethernet switch, router, firewall, SAN switch, Network card, Network-Attached Storage (NAS), and fiber media converter.

7. Will SFP+ module work in SFP port?

The SFP+ module cannot typically be used in an SFP port because SFP+ usually supports speeds of 10 Gbps, while standard ports are limited to 1 Gbps. Although SFP and SFP+ ports may look similar, they have different performance capabilities. However, if a dual-rate 1G/10G SFP+ module is used, it may work in a 1G port. The key factor is ensuring that the optical module’s speed matches the port’s requirements.

8. What is the maximum number of SFP ports an Ethernet switch can hold?

A: It depends on the manufacturer’s design and intended use of the switch. But since most switches are 1U size, the limited space can only hold a limited number of SFP ports. According to our research, most switches hold 2 to 32 ports, and only very few high-density switches hold 48 SFP ports. That may be the most count for the 1U networking switch.

Final thoughts

I hope you enjoyed my guide to SFP ports. Now, you should know their meaning and the different types. 

What types of ports are in your switches? 

Do you plan to upgrade SFP switches to QSFP28 port switches?

Are there any topics missed in this post?

Let me know by Leaving a message now.

Read more:

• Should you Buy OEM Optics or Third Party Optics?
• Understanding 100G Ethernet
• What is SFP Module? An Ultimate Guide
• Ethernet Switch Port Types: A Complete Guide