RJ45 vs SFP Port: Which Should Be Used to Connect Two Switches?

Updated on Dec 29, 2021

Both run at 1000Mbps but differ a lot based on different connection types

Enterprise Switch

It is always a question to choose an access switch with SFP ports or RJ45 Ethernet ports for 1000Mbps connections. RJ45 port vs SFP port, many people wonder the main differences between them. Is RJ45 port or SFP port that suits your network? As RJ45 port and SFP port are already quite familiar to most users, here are some principles that we could follow to choose between RJ45 port and SFP port while skipping the repeated introductions of what is SFP port or RJ45 port.

Difference between RJ45 and SFP port in 1000Mbps Connections

Connection Types

It’s the most basic difference which decides many other features of RJ45 ports vs SFP ports, so we put it at the very beginning. RJ45 ports support RJ45 Ethernet cables such as Cat5, CT6, etc., commonly be used to connect a computer or a router. What are SFP ports used for? In terms of SFP switches, SFP ports are more versatile and accept fiber SFP modules with fiber optic cables (both single-mode and multimode), as well as copper SFP modules with Cat5e, Cat6, Cat7, Cat8 cables.

Maximum Distance

The maximal transmission distance varies a lot due to the connections RJ45 and SFP ports used respectively. RJ45 ports support a maximum distance of 100 meters, making it more than enough for a home or small office network. SFP ports allow greater distances. MMF cables connected to the SFP port can reach up to 550-600 meters and SMF cables 150 kilometers. If connected with a Cat5 cable, the SFP port follows a 100-meter limitation.

Features SFP Port RJ45 Port
Connection Types
  • copper SFP module + RJ45 Ethernet cable (Cat5e/Cat6 or higher)

  • fiber SFP module + fiber optic cable (SMF fiber / MMF fiber)

RJ45 Ethernet cable (Cat5e/Cat6 or higher)
Max Distance MMF (550m) / SMF (150km) / RJ45 Ethernet cable (100m) 100m (330ft)
Data Rate 1000Mbps (1G) 1000Mbps (1G)

Actually, here comes another related network switch port type, which is the combo port. For example, this S5800-8TF12S switch comes with 8 x 1G SFP/RJ45 combo ports, and 12x 1G/10GE SFP+ ports. Compared to SFP/RJ45 ports, these 8 combo SFP/RJ45 ports allow users to use either SFP port or RJ45 port at a time for short-distance connections.


Considerations for Choosing RJ45 or SFP Port

Now we know when the link distance is over 100 meters, SFP port with fiber SFP module must be considered instead of RJ45 Ethernet port with Ethernet cable. People may also want to learn about SFP 1000Mbps vs RJ45 1000Mbps when the connection is within 100 meters. Here are some other principles when deciding to use RJ45 port or SFP port.

  • Security. Using fiber SFP module is more secure than Cat5e/Cat6 RJ45 Ethernet cable in some worse circumstances. RJ45 cable uses electric current so it can be easier to catch on a fire/lightning while fiber SFP module has no such problem.

  • Reliability. Fiber is often considered more reliable due to its properties. RJ45 Ethernet cable has the risk of EMI (Electromagnetic Interference) since it uses electric signals which can be easily affected by some external elements, such as high voltage.

  • Latency. When connecting devices at a considerable distance, SFP ports have a lower latency compared to RJ45 ports that maybe give a worse service.

  • Power Consumption. SFP ports have lower consumption compared to RJ45 ports. Especially in a large network, the consumption difference is going to be far more obvious.

  • Future Network Upgrade. If you’re planning to move to higher bandwidth, e.g. 10 Gbps, in the near future, SFP ports that support fiber optic cable are more future-proof compared with Cat5e/Cat6 RJ45 Ethernet cable.

  • Cost. Since RJ45 Ethernet port and SFP port actually run at the same speed, choosing RJ45 ports to connect Ethernet switches might be more economical as Cat5e/Cat6 cable is lower-priced than the SFP connection with both transceivers and corresponding cables.

RJ45 vs SFP Port Application Scenarios

Except for the above principles for choosing SFP 1000Mbps vs RJ45 1000Mbps, this part will introduce some real cases to give you a better understanding of the selection between RJ45 and SFP port.

Connections Between Two Buildings

Case description: Two Gigabit switches are needed to connect two buildings 300 feet (91 meters) apart. For RJ45 switch vs SFP switch, which one should we choose?

Case analysis: For cost-saving, using RJ45 switches is better to connect the two buildings. In reality, more factors should be considered since the network switches are in two buildings. Firstly, if the two buildings have separate electrical power inputs, then running copper between them could cause ground loop issues, so go fiber. Secondly, lightning strikes might matter when using copper cable across buildings, so goes fiber. If neither fiber or copper cabling is feasible, that is to say, RJ45 ports and SFP ports can not function well in this situation, just go wireless.

building connection

Connections in the Racks

Case description: When building connections in the same rack, it seems SFP ports are always used instead of RJ45 Ethernet ports. Why use SFP ports in this situation though this solution costs a lot?

Case analysis: This is about connecting 1000Mbps switches on the same rack. SFP port is used instead of RJ45 port which can cause electrical interference. Another reason could be power consumption. When there are more than 100 links, choosing SFP ports is more power-saving than Ethernet ports.


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